DIYstompboxes.com

I've decided that a cool project would be a solid state amp. I will be designing this, getting professionally manufactured PCBs as with my previous projects, and creating a detailed PDF to help you build it.

Design considerations:

1) Approximately 20 watts.

2) About as easy to build as an effects pedal. This is the big thing for me. I know that many people aren't confident doing mains wiring, or else are more confident than they should be and end up doing unsafe wiring. So this project will be powerable using a pre-built and easily available power supply. No high voltages, no transformer to track down.

For the rest of the details, I turn to you guys, the forumites, to ask what you'd want in a DIY solid state amp.

Questions for you:

1) Do you want this to have an integrated preamp, or just act as a power amp to drive a speaker to decent volumes?

2) If yes to 1, do you want EQ?

3) If yes to 1, do you want switchable channels? Clean/OD? We could even do a relay-based footswitch for channel switching.

In other words, do you want this to just be a power amp, to be married with whatever preamp, overdive, reverb etc. of your personal choosing, or would you like to see this as more of a full-featured standalone amp? I'd probably just want a power amp for myself, but it's not too difficult to add a preamp with overdrive to the PCB, so if enough people want that, we can do it, and if you don't want to use it, it will be easy to bypass.

Let me know your thoughts.

I made a poll for the questions, let's see if this works:

http://www.ballot-box.net/service3/poll.view.php?pollid=23271

Cool ballot idea. I think there's a way to do survey's here, but I think you're limited in choice.

Also, along with this project, it would be cool if we could get someone who's handy with the amps (I'm looking at those guys over in the amp picture thread) to draft plans for either a 1x10 or a 1x12 combo we can fit this kind of thing into. I don't know how to source parts for the chassis and stuff needed for putting a whole amp together, but perhaps putting links to where you can get everything to build yourself a solid state amp from scratch and plans to do it would be something even the Kit companies out there haven't been able to do yet!

Jacob

That's an interesting idea. I'm just going to work on the amp itself, but perhaps info will spring up along the way on how to build a cab or combo.

Hmm, from the poll, some definite trends are beginning to emerge. Looks like everybody wants a preamp.

I didn't intend for the poll to preclude discussion here, only to give a clear view of the numbers. But I do want to encourage people to discuss these things in the thread as well.

If they are kept on separate boards people can have their own special preamps

That was my thinking too, but it looks to me like everybody wants an integrated preamp. If it continues to be true that most people want that even if there are dissenters, it would still be easy to bypass an integrated preamp for those who want to do so.

A preamp input would be an excellent excuse for me to save up some cash for a Murder One.

By preamp input, do you just mean an input directly to the power amp, bypassing the integrated preamp? That will definitely be possible.

My vote is a power amp with a high input impedance and volume knob!

High Impedance Buffer -> Volume Knob -> Power Amp

Quote from: Taylor on September 10, 2010, 11:46:06 PM
By preamp input, do you just mean an input directly to the power amp, bypassing the integrated preamp? That will definitely be possible.

This would be a great idea. As I wrote in your other thread (http://www.diystompboxes.com/smfforum/index.php?topic=86887.0) I try to build a practise amp based on a TDA2040 (circuit from data sheet) & Sansamp GT2. With send & return.
Maybe I can finish this thing this month....

  Dave's vote certainly makes his post a more simple project, same thing would go for the amp, driving it with even a boost probably would 'kick it into high gear', that or a Fuzz, will sound a bit different of course with a preamp' or high headroom boost driving it.
 k..here's ways to do it..I always think it's best to start at the far end of the chain when designing any audio production system.
 Starting with the speaker, choosing it for:
 Effeciency [how loud per certain watt range
 Eq [what frequencies does it make the loudest
 Resonant peak [which ones make it resonate
 Compression [has to do with cabinet maybe
 ...anything else like cost, weight, size.
 That^ said, immediate availablity [ie I own it now] has often been the #1 consideration for speaker choices [especially around the time of affording a 1rst power supply and amplifier build]. I've been lucky and scrounged some decent speakers [old stereo stuff has occasionally been a good source], if the operator understands the limitations of a limited speaker and stays within it..great, reliable sound can be the result, if the speaker is near limit and clipping is presented to it...not so much. Basically to have a sweet relationship between a SS output and a speaker requires proper matching or proper volume control management, over-driving a too small speaker or amp clipping is never recommended.
 Then the next thing [besides good speaker wire] is the amp.
 Have others help you choose a chipamp, I have a 3875 @18v I like a lot, 18 was chosen because it was there [clean and portable power] bigger voltage certainly adds and doesnt really subtract anything from the SS amp performance until it nears the max. So this really depends on the speaker-loudness and how loud you want to get, the idea is run the amp clean [no peaks clipping] at all times, I've peaked the amp and it was only horrid, not super-ungraceful to seeming dangerous with the 12'' GB speaker at the time.
 Reading the data sheets on the chip features:
 What kind of protection features, what are the power supply options/demands..anything else you can dig up. Plenty of chip experiences to draw from around here.
 Once the data sheets are understood the amp instructions are also available at Chipamp.com and other places, choosing the filter capacitors and whatever else [snubbing caps?] for the design[s..a lot of options sorting.
 The amp/supply should be capable of at least getting the speaker 'going', [or having a loudness type control?] so lower volumes have the frequencies / tone 'filled in' sounding...yet another option, however.
 That would be in the category of Tone Control, I would say since the tone control introduces passive losses, it might be a nice feature to have a preamp drive it. By preamp I mean something that drives the TC [so it works right] and enough to drive the amp past 1/2 volume also comes in handy right in the package with 1 handle. Most ampsters agree that TC is a nice feature, allowing frequency adjustments for speaker volumes, room textures and sizes, where the speaker is located etc. And one unit that gets the speaker[s fairly loud includes the preamp.
 Since I'm not using that many effects with my 18v, I used a 3/2 Jfetzer preamp, and that generally gets the amp up to or over what the 18v supply imposes as a headroom level. The supply [battery] uses a polarized jack/plug [2 conductors worth of a computer supply bundle] allows various supplies to safely be used, I would have preferred a chassis mounted jack, mounting the heavy wires seems workable though, I used pressure-cooker pots for my..pressure cooker amps ! Chassis choice of course is a necessary evil.
 Otherwise, a hefty output from a booster or fuzz generally produces enough input voltage to outdo the 18v supply and <18v output before clipping. Even a well voiced booster on the same supply can produce enough to satisfy to some extent what the amp [and speaker] expect as input...the amps really need 'something/anything' as a boost up, a hot output guitar gets them strong enough to know it's working, but won't 'fill in' the tone.
 So...it could be a plain amp, and working with various preamp designs [ie to get the voltage up enough to drive the chip input] will be needed, choosing 'the one' [could be two I suppose...why not? it complicates discussion.]..anyway, I've done that, and having a clean and slightly dirty side...got amende-chopped to a slightly dirty /cleanish Jfetzer [I think it's a decent choice, it goes with dirtpedals pretty good, and cause although super-clean is cool, I prefer it with a slightly dirty boost 90% of the time..rolling back the G-volume of course a cleanup option.
 2,000 types of speakers to choose from [or more often just the one that is ready available]. I like the little alnico's or a 10'' or 12'' speaker with the chipamps @ lower voltages, getting up to around 35v or so [since that's what i've tried] pumps an old EV-15B ok. If super frugal about amp building, a 'more suitable' new speaker may constitute about 1/2 the cost of the project, figureing this part out [and the cabinet] can be a little tricky, depending on how much the used/free market is searched...and how much is actually known about x, y, and z speaker.
 For the criterion you've established, around 30v supply [if it can be figured out without mains wiring is suggested, suitable current capability] would be able to get more out of the chip and still be relatively innocuous as far as safety.  
 >18v chip supply recommended though, and begins to make the amp capable of 'starting up' most speaker types enough to get 'going', and not be an Eq problem.

I have built the vellman ss amps of the 3 watt and 7 watt type and both sound reallly good for what they are. You can fit either of them into a smaller hammond box easily. Both are simple and sound decent when driven by a ts or other pedal. Both sound good when driven by valvecasters as well. I think something like a ts or even a lm386 based preamp/distortion channel thast bypassable to just a power amp with a hi impedenced master volume input would be sweet amd easey to do. A tube pre would be an easey option as well. Just my thoughts. I think the tda2003 chip amp is simple and can run on a 9 ,12 or 15 volt supply and does around 5 to 7 watts.

I've looked into SS power amps quite a bit. The cheap route to go is to use either a 2N3055 pair or a 2N3055/MJ2955 compliment. They're still readily available and a lot of amps have used these in the past (meaning lots of reference designs). Two of either flavor (NPN or PNP/NPN) will put out well over 20W though, more like 100-150W if you get the heat out right. But keeping them well under their rated dissipation would work in your favor, you could simplify some of the requisite protection circuitry and could perhaps simplify or completely eliminate the heatsinking as well (or use the PCB for heatsinking). Just a thought as most high power amplifier IC's are relatively expensive.

Another route to go would be to look into some of the TI class D power amp IC's. They are easy to design with, offer cheap and efficient power and have good enough linearity for anything we are concerned with. Something like the TPA3112 will do 20W into 4 Ohms and I'm sure would sound fine as a power amp (just don't distort it!!).

for powersupply, both for your own convinience and to possibly to get around liabillity issiues, I'd suggest you use a ready made, store bought 24volt/60watt Laptop powersupply
a few extra caps and resistors could sort and powersupply whining..
J

So something like that  i suggested 40 watts tda2030 beefed with two medium power transistors and 12...44 volts supply circuit might be nice, seems easy and cheap and low parts count too, might be loud nough with drummer if the speaker cabinet is efficient

just bought two supercheap 10" guitar loudspeakers, someone said they are "fenderish" but that might be sales talk...

Interesting options.

The 2n3055-based amps seem to want something around 60v. But the TPA3112 seems to run on a lower voltage.

For me, the big thing here is to make this project easy. It should hopefully be about as easy and safe to build as a guitar pedal, and not require any difficult-to-source parts. There are already tons of great DIY amp projects put together by people infinitely more knowledgeable than I, so my intent here is not to outdo what has been done from an engineering perspective, but to make something that relative novices can build and enjoy. So to that end, I want to do something that can be powered by an easy-to-find laptop power supply. I was planning to use the TDA7240A chip, but I will be looking into all of the suggestions here.

I can definitely say that a tube preamp will not be a part of this project. However, part of the idea of this was to make an amp PCB that's small enough to be paired with whatever preamp and other stuff you want. It's looking like most people want an integrated preamp and EQ, however this will of course be bypass-able, so it would be easy to pair it up with a tube pre of your choosing, parametric EQ, spring reverb driver with reverb tank, etc. I guess maybe down the road, if people were interested, I could do add-on boards to provide this kind of functionality - so this could be a kind of modular amplifier where you just build the sections you want, so you can have an insane monster with 3 tube channels, each with their own EQ, etc. But for now I'd like to keep it simple.

I like the idea very much, Taylor! Why not have a PCB with lots of space in the pre-amp section for modding, adding extra channels etc.?
Also, a chip like the 2030 (and other ic's prabably as well) will give you many options for different poweramps: by varying the power supply you could have versions ranging from like 6 tot 18 watts, by adding some  transistors, like Nasse said, you can go up to 40 wats. Two poweramps and  2 spaekers, sharing the same preamp channel(s) would double this output...
Kind of like the AX84 module idea, always liked that.
Maarten

I have a couple of tda1514 at home, not sure they are good for guitar, and I heard it's not produced anymore... so this is probably not a good suggestion for the present project... well...
I was just planning to try and build something with it.. I'll let you know in case..

but I think the whole automotive TDA range of amplifier is the easy way to go...

Here's another thought for the "amp requirements": make is play well with effects! Some amps (especially SS ones) tend to have issues with distortion effects. I agree with making it easy to build, but this is a stompbox forum and I think the compatibility issue should be of equal importance.
-Joe Hart

Quote from: Joe Hart on September 11, 2010, 07:10:41 AM
Here's another thought for the "amp requirements": make is play well with effects! Some amps (especially SS ones) tend to have issues with distortion effects. I agree with making it easy to build, but this is a stompbox forum and I think the compatibility issue should be of equal importance.
-Joe Hart

Yes, I agree. Everyone builds there own FX, especially here.
An amp that takes pedals well is the way to go.
Just something simple with a volume knob would please
most of us. Making a preamp module to go with it is another thing
but an amp that takes pedals well is 90% of the battle.

Quote from: Taylor on September 11, 2010, 04:37:45 AM
Interesting options.

The 2n3055-based amps seem to want something around 60v. But the TPA3112 seems to run on a lower voltage.

For me, the big thing here is to make this project easy. It should hopefully be about as easy and safe to build as a guitar pedal, and not require any difficult-to-source parts. There are already tons of great DIY amp projects put together by people infinitely more knowledgeable than I, so my intent here is not to outdo what has been done from an engineering perspective, but to make something that relative novices can build and enjoy. So to that end, I want to do something that can be powered by an easy-to-find laptop power supply. I was planning to use the TDA7240A chip, but I will be looking into all of the suggestions here.

I can definitely say that a tube preamp will not be a part of this project. However, part of the idea of this was to make an amp PCB that's small enough to be paired with whatever preamp and other stuff you want. It's looking like most people want an integrated preamp and EQ, however this will of course be bypass-able, so it would be easy to pair it up with a tube pre of your choosing, parametric EQ, spring reverb driver with reverb tank, etc. I guess maybe down the road, if people were interested, I could do add-on boards to provide this kind of functionality - so this could be a kind of modular amplifier where you just build the sections you want, so you can have an insane monster with 3 tube channels, each with their own EQ, etc. But for now I'd like to keep it simple.

Going discrete or class D is definitely not the simple solution. The TDA7240 looks like a nice option for what you are trying to do. Good luck!

That looks good to me.  The TDA7240 seems like a good chip to go with.  You would have an easy time with the power supply then.  I would still suggest an amp that has a chain as follows:

High Impedance Buffer -> Equalizer -> Volume Control -> TDA7240

I would like to see no pre-amp as far as distortion type of effects.  Mostly I say this since the majority of people here I would think have lots of effects boxes that do this type of thing.  I would like to see a power amp that basically takes what your effects puts out and amplifies it for the speakers without any thing else happening in the amp.  Kind of like a poor mans Tech 21 Power Engine.

I take bus drivers' holidays, obviously. I design effects all day, and then for some relaxation to get away from it all on nights and weekends, I design audio gear for myself (well, and you guys, obviously).

I just finished up a set of PCBs which replicate, in detail, the circuitry inside the Thomas Vox Super Beatle. This includes the normal channel with midrange boosting, the brilliant channel with the embedded distortion effect, the tremolo, the reverb, the mixer/limiter (which I think is the key to the sound these things have) and the repeat percussion. Well, OK, the power amp too. It's a complete set of boards less the power supply for the amp.

This got started when I got frustrated at the yards of overlapping wiring inside the Thomas boxes. The problem is that they use one big PCB and run wires to all the controls. What I did was to separate the circuits by which control they were wired to, and made small PCBs that did one thing and stuck to the backs of the pots with adhesive standoffs, so the wires to the pots, jacks, switches, etc. are only a couple of inches long. The wires into and out of each module are power, ground, signal(s) in and signals out. This approach of putting the circuits near the controls dramatically cuts down on the wiring from module to module and makes the wiring easy to troubleshoot if it does happen to break.

I also reworked the power supply setup from the old cap-resistor-cap-resistor-cap-resistor... to putting a three terminal regulator on each board. The TO-92 regulators will do fine for the local power needed by one board, and mean that you don't need all the power supply junk, just a feed from the main power supply to run the boards; it's converted to the voltage needed local to the module/PCB, and also regulated so it does not have ripple and interaction issues.

The power supply for all these amps is pretty much what you'd use for an LM3886 power amp chip, that being +/-31V at no load, and all but one of the modules run from +31V only. This is a 42Vct power transformer, a diode bridge, and two 4700uF filter caps. As noted, the 2N3055 is the power transistor the original circuit used, and I have reverse engineered the driver transformer that the original circuit used, in addition to making a PCB for the power amp. So you could either use one LM3886 per speaker to get as much power as you want - literally unlimited except by the power supply(s) you want to build and the number of heatsinks and LM3886s you want to hook up to the preamp out. You get 30W per speaker per LM3886 with no particular strain on the LM3886.

A big part of the sound of these amps is the mixer-limiter, which pre-limits the audio getting to the power amp so the power amp never clips. That means the characteristic overdrive sound of the amp is more the sound of the mixer limiter than the sound of overdriving the power amp.

Anyway, that's how I spend my fun, get away from it all time. I had to order five board sets to get the one I'm putting together for myself.

Hey, Taylor I like where this is going.
I have been considering either buying or building another small amp just this week.
If I may offer one suggestion , it would be a row of pads along one edge of Your PCB that could be used for EQ or a loop or reverb or whatever, and if not required then they are just bridged with links.
Good luck !

It's well to remember that the electronics are the easy part. What's HARD is building an amp enclosure, speaker cabinet, sheet metal chassis, getting the AC wiring right, all the stuff that's NOT putting resistors and chips onto a PCB. It's like Effects Economics 101 from the Guitar Effects FAQ at GEO, but on steriods.

There is a neat solution you can work if you're motivated and patient.

I bought a fully working 100Wrms guitar amp combo with 2-12" speakers in it for $40 a while back on Craigslist. It's a "Rogue" brand - which is a Musician's Friend house brand. It sold for $400 new, and in general has a dreadful sound unless you like squeeky clean and not working well with effects.

However, all the hard part is already done: there's a speaker enclosure with speakers, already wired up, a power supply, a sheet metal chassis, and a generously sized space inside for adding in parts. I intend to use it for a "soul transplant" of a repro of the circuits of a JMI Vox Supreme amplifier. I've seen these on craigslist for $40 to $100. If you have ever looked at the amount of work involved in building an amp and speaker cab out of boards, glue and tolex, this is a major bargain.

Quote from: R.G. on September 11, 2010, 02:16:35 PM
It's well to remember that the electronics are the easy part. What's HARD is building an amp enclosure, speaker cabinet, sheet metal chassis, getting the AC wiring right, all the stuff that's NOT putting resistors and chips onto a PCB.

Right, this amp is intended to obviate most of that. It will fit in a standard Hammond box. No AC wiring.

As far as building a speaker cabinet, I see that as entirely separate from building an amp. The kinds of speaker cabs people use will all be drastically different (for example, as a bass player, I have no use for an open back little 12" cab, nor for a Marshall-style shallow-backed 4x12), so I'm not going to get involved with speaker cabs. This will just be an amp.

If one makes a PCB set to sell and the circuit plugs into the wall,      What is the liability?

9VDC battery powered effects are a bit different than a plug in the wall build, built by someone maybe not aware of how to build and operate the circuit safely.  Say the person builds the circuit wrong and a house burns down and/or people are hurt or worse.   Who is going to get blamed/sued?

Then you have ROHS.

I see what you mean gus but if I sell you a fork and you stick it in a wall outlet then what?
Taylor would just be selling a piece of fiberglass with holes in it.  (I think)

Quote from: Taylor on September 11, 2010, 02:47:34 PM
Right, this amp is intended to obviate most of that. It will fit in a standard Hammond box. No AC wiring.

That's good, and simple. Obviating issues is good. But Mother Nature is waiting for you at the end of the assembly line in the form of waste heat.

If something dissipates 1W how hot does it get? The correct answer is "the temperature is unlimited; it will rise in temperature until the 1W gets out and it comes into balance between power out and power in." There is no limit to temperature, only a balance between power in and power out. Temperature is just the "pressure" which drives the transfer. A 300mW incandescent bulb filament gets to over 1000C because it has no way to get the heat out other than getting hot enough to radiate it away as photons. It has a high thermal resistance from the heat source (filament) to the rest of the universe, so the temperature rises until the power gets out.

A standard Hammond box is at least theoretically a heat sink, but not an ideal one. I have not done the necessary test, but I heavily recommend that you do. Get a Hammond box of the size you intend to use, stick a power resistor down on the inside of it with some heat sink goo where you think you're going to put the power transistors or IC from the amp, and run DC into it to make it dissipate 1W, 5W, 10W, etc. while you measure the temperature of the hot spot on the outside of the box where the resistor is. The box is accepting heat from the heat source, and spreading it out while radiating and conducting it to the surrounding air. So the box gets hottest under the heat source, and cools as it spreads heat out and transfers it to air along the way. There is a per-unit thermal resistance from each unit of area of the box to the air, and also a spreading resistance caused by the flow of heat from the heat source through the metal. That impedes heat flow too.

Heating it and measuring the hot spot temperature lets you directly measure how much power you can put out. All transistors and power amp chips have a maximum case temperature you can let them run to. For the TDA2030, the limit is 20W of dissipation at Tcase=90C. This is because the chip has an internal temperature limit system which keeps the chip from going over 150C, and the thermal resistance from the chip to the outside heat tab of the case is 3C/watt. So with 20W dissipated inside, the chip gets to 150C when the tab is 90C. The heat has to get from the tab to the outside air. A mica insulator and heat sink goo will resist by about 0.5 to 1 C/watt, so the temperature of the surface the chip plus insulator is mounted on will have to be less than about 70-80C. Otherwise, the chip will simply go silent without warning until it cools back down. With outside air at maybe 30C, that gives you as little as 40C rise for 20W, and that means you have to have a heat sink which has a resistance of not more than about 2C/W.

Will a Hammond box do that? I don't know. I haven't measured one. But I HAVE measured a U-channel of 1/8" thick aluminum three inches wide and seven inches long oriented so air could flow over it vertically, which is the best condition for heat dissipation. That used both sides of the aluminum to get rid of heat. It measured 2.7C/W. Hammond boxes are cast aluminum-zinc alloy, which conducts heat less well than pure aluminum.

Another way of looking at this is the power you can get out of the chip is limited by how much the thermal resistance of the heat sink is. You can't get any more out than the chip will withstand without shutting down. So one way out of this is to back down the power supply voltage until the waste heat fits within the Hammond box limits for heat removal with the box temp under the chip at 90C. That's the real limit to how much power you can put out.

Interestingly, 90C surfaces will give you an unpleasant burn if you touch them.

One reason this is all familiar to me is that Rick Vance followed exactly this trail when he got into building solid state guitar amps with an LM3886. This was the origin of the ssguitar.com web site. He thought he had done a defective build but he was really just overtemping his chip with too small a heat sink.

QuoteAs far as building a speaker cabinet, I see that as entirely separate from building an amp. The kinds of speaker cabs people use will all be drastically different (for example, as a bass player, I have no use for an open back little 12" cab, nor for a Marshall-style shallow-backed 4x12), so I'm not going to get involved with speaker cabs. This will just be an amp.

That's OK. It's easy to find speakers in a cab. But you'd be doing the builders a real service if you also told them something about cabs and where to get them or how to build them. I was always very frustrated when I tried to hear what I was playing by feeling of the output wires.   :icon_biggrin:

Quote from: Gus on September 11, 2010, 03:40:50 PM
If one makes a PCB set to sell and the circuit plugs into the wall,      What is the liability?

9VDC battery powered effects are a bit different than a plug in the wall build, built by someone maybe not aware of how to build and operate the circuit safely.  Say the person builds the circuit wrong and a house burns down and/or people are hurt or worse.   Who is going to get blamed/sued?

Then you have ROHS.

Once again, there will be no AC wiring, no high voltages. This amp will be powered by a pre-built laptop power supply.

Quote from: R.G. on September 11, 2010, 04:06:03 PM

A standard Hammond box is at least theoretically a heat sink, but not an ideal one.

Sorry, I guess I should have put a lot more info about what I was thinking in the first post. I don't intend to use the box as the only heatsink; there will be a real heatsink. Of course, there are mechanical considerations w.r.t. how to attach the heatsink to the chip while the board is in the box, etc.

Quote
That's OK. It's easy to find speakers in a cab. But you'd be doing the builders a real service if you also told them something about cabs and where to get them or how to build them. I was always very frustrated when I tried to hear what I was playing by feeling of the output wires.   :icon_biggrin:

I see what you're saying, but to me amp and cab have always been separate things, so I don't really feel that it's necessary to mix this project with a speaker. It's just that everybody will have drastically different ideas about speakers, all of which are mutually incompatible. So for example, I'm ok with having an integrated preamp in this amp, as it's only a few more parts and a little bit of board space, and can easily be defeated for people who won't use it. But designing a speaker cabinet to go with this amp would be lots of work, and would be useless for all the people out there who don't play guitar (including myself), or guitarists who don't like 12" speakers, or people who prefer sealed cabinets, or people who want a horn-loaded design, or people who want a 3-way crossover with mid speaker and tweeter, etc. This amp will be useful (I think) to a wide variety of players, but any particular speaker design would be inherently limited to a very small subset of players.

To me, a solid state amp, being small and electronic, is more at home being integrated into a pedalboard than into a speaker cabinet. My idea here was to make an amp that could be put on your pedalboard if you want, and then you can just run a speaker cable to the cab. This facilitates simpler, easier patching from effects loop to pedal, etc, and makes unnecessary the need to run power to your amp on top of your cab.

But, of course there's no reason that I can't link to a bunch of info on building guitar cabs.

Quote from: John Lyons on September 11, 2010, 12:36:46 PM

Quote from: Joe Hart on September 11, 2010, 07:10:41 AM
Here's another thought for the "amp requirements": make is play well with effects! Some amps (especially SS ones) tend to have issues with distortion effects. I agree with making it easy to build, but this is a stompbox forum and I think the compatibility issue should be of equal importance.
-Joe Hart

Yes, I agree. Everyone builds there own FX, especially here.
An amp that takes pedals well is the way to go.
Just something simple with a volume knob would please
most of us. Making a preamp module to go with it is another thing
but an amp that takes pedals well is 90% of the battle.

I think I've read a bit about this topic, but can you guys explain a little about what makes an amp take pedals well? Or maybe more to the point, what makes an amp play poorly with pedals? I've never really experienced this mismatch, but it might be a guitar thing which would explain why I never noticed.

The classic word I've read about that gets thrown out there for amps that 'take pedals well' is "headroom". I assume this means, to those who use it at least, that the amp has lots of room to be 'pushed' with a hot signal, and handles that without distorting or becoming unpleasant to listen to.

At first when I heard you say, "this is meant to be put in a hammond box" I was turned off. I want to be able to build this into an actual amp cab and have it work well for me. I think if I can manage to do that, or find someone to help me figure out how to do that, we can easily link the neccessary files to the project, as you can the files for a hammond box as a pedal board amp. I like that idea too, and will likely build one of each.

I had a question for you though Taylor: Could you design this to accept a variety of power supplies? Obviously you have one idea, but perhaps I wanted to build an internal power supply with your usual power cord that I could plug into my PP2+ power supply on my pedal board. I like RG's idea of having a seperate board for all sorts of functions in an amp - perhaps we could have 3 boards: Preamp, Poweramp and Powersupply. I also really like the idea of having a bunch of pads for things like a Reverb output and an effects loop and such.

What are we thinking for the preamp? What about something in the style of ROG that emulates a good amp? I was thinking a Blackface Fender Twin myself, clean and pristine with 3 band tone control. I'd also love to see a Bassman preamp, which might be good for the Bassists out there along with the guitarists (half serious). If we were to have channel switching (My vote), an 18 watt marshall type could be good.

Jacob

Quote from: jkokura on September 11, 2010, 05:58:20 PM
The classic word I've read about that gets thrown out there for amps that 'take pedals well' is "headroom". I assume this means, to those who use it at least, that the amp has lots of room to be 'pushed' with a hot signal, and handles that without distorting or becoming unpleasant to listen to.

At first when I heard you say, "this is meant to be put in a hammond box" I was turned off. I want to be able to build this into an actual amp cab and have it work well for me. I think if I can manage to do that, or find someone to help me figure out how to do that, we can easily link the neccessary files to the project, as you can the files for a hammond box as a pedal board amp. I like that idea too, and will likely build one of each.

Well, if it fits in a Hammond box, it would easily fit into a guitar cab. The opposite is not true - if I design it to fit into a particular wooden cab, it wouldn't fit into a small metal box for people who want to put it on their pedalboard.

QuoteI had a question for you though Taylor: Could you design this to accept a variety of power supplies? Obviously you have one idea, but perhaps I wanted to build an internal power supply with your usual power cord that I could plug into my PP2+ power supply on my pedal board.

No, the idea is that I want to avoid making people do mains wiring. It's dangerous and it turns a lot of people off. There are already plenty of amps with power supply boards available, so there's not much use in another project like that. But you could easily build the laptop supply into the same box if you just want them physically connected.

QuoteI like RG's idea of having a seperate board for all sorts of functions in an amp - perhaps we could have 3 boards: Preamp, Poweramp and Powersupply. I also really like the idea of having a bunch of pads for things like a Reverb output and an effects loop and such.

I would like to have patchability, but there definitely will not be separate PCBs. Doing that increases the cost a lot without much payoff. The preamp section and power amp section will be separate unless you patch them together, so you don't have to build the pre if you won't use it, or you can bypass it easily.

QuoteWhat are we thinking for the preamp? What about something in the style of ROG that emulates a good amp? I was thinking a Blackface Fender Twin myself, clean and pristine with 3 band tone control. I'd also love to see a Bassman preamp, which might be good for the Bassists out there along with the guitarists (half serious). If we were to have channel switching (My vote), an 18 watt marshall type could be good.

Jacob

Something like that is a good idea. I wouldn't want to yoink anything from ROG but that's a good direction to go in.

No, the schems for the amps are out there. The hard part will be take the tubes and finding out how to make them solid state circtuits instead. I don't know how to do that, but obviously people do with all the Amp emulating pedals out there, both DIY and commercial (Tech 21)...

Jacob

The Tech21 stuff, at least the modern stuff, is all opamp based, no JFETs as far as I know. Those have fairly large parts count, so I think for the preamp I'd like to stick to something a little simpler, I guess in the vein of the ROG JFET things, or an opamp with diodes in the feedback loop kind of thing. I'm going to wait a few days to see how the poll goes, but since it looks like nearly everyone does want a preamp and a 3-band EQ, I'll be doing another poll to decide what kind of preamp (and also try to figure out the presence or absence of switchable channels, since that question does not look as unanimous on the poll so far).

Quote from: Taylor on September 11, 2010, 06:23:36 PM
I would like to have patchability, but there definitely will not be separate PCBs. Doing that increases the cost a lot without much payoff. The preamp section and power amp section will be separate unless you patch them together, so you don't have to build the pre if you won't use it, or you can bypass it easily.

This I like, if I'd like to include a mixer to mix in an aux (mp3) signal all I'd have to do is "take" the signal between the pre and power amps and do whatever I want with it. Make sure you consider all points where someone would want to insert there own processing (though I can only think of the intersection between pre and power right now and maybe bypass the tone stack or replace it with a custom). I think what my tired and slightly drunk mind is ambling towards is a mod-able design for those inclined.

I also like the fact that I suggested this type of project in your other thread :)

While I do like this project, I also like the fact that there'll probably be a while before I actually start building one myself as I got an Orange Crush Pix CR20LDX for my 40'th birthday (sept 11, hence tired and drunk, 2 am here now and I'm off to bed now)  ;D

I would like to know what power supply is gonna be used.
You mentioned a laptop supply but arent most of those switching power supliers?
I just dont see where you are gonna get 20 watts at the spkr,with a small Hammond box and a laptop supply and still have it fit on a pedal board.
I will be watching with interest,even though I have enough amps both SS and tube.
And several that need to be finished.
But your design goals are whats peaking my interest,how you solve them should be very enlightning to me.
Good Luck with this Taylor!

20 watts ,a small enclosure that fits on a pedal board, and no mains wiring or internal transformer.
Sounds like the EH .22 practice amp.

Quote from: Brymus on September 11, 2010, 08:22:06 PM
I would like to know what power supply is gonna be used.
You mentioned a laptop supply but arent most of those switching power supliers?
I just dont see where you are gonna get 20 watts at the spkr,with a small Hammond box and a laptop supply and still have it fit on a pedal board.
But your design goals are whats peaking my interest,how you solve them should be very enlightning to me.
Good Luck with this Taylor!

Waltk has basically already done it:

http://www.diystompboxes.com/smfforum/index.php?topic=86887.msg729085#msg729085

Cool idea!

I'd ideally like to see something like a Crate Powerblock, but scaled down for simplicity (as you've already mentioned).

I discussed something like this on another forum:
http://circuitworkshop.com/forum/index.php?topic=547.0

The only thing not mentioned here is the inclusion of an effects loop, which I would be most interested in. I think the loop is left off of too many small amps.

Since the preamp and power amp will not be hardwired together on the PCB, an effects loop would just require wiring up a pair of switching jacks.

I agree about the Powerblock - 100 watts would be great. But since 10 times power equals twice the perceived loudness, 20 watts is only half as loud as 200. To put it another way, I don't think enough would be gained by going up to 100w to justify the added cost, size, and complexity.

Quote from: Taylor on September 11, 2010, 09:41:30 PM
I agree about the Powerblock - 100 watts would be great. But since 10 times power equals twice the perceived loudness, 20 watts is only half as loud as 200. To put it another way, I don't think enough would be gained by going up to 100w to justify the added cost, size, and complexity.

That's why I said it should be scaled down. ;)

20w - 40w would be fine with me.

I think this project is a great idea, however I think the issue will be coming up with a competitive price for the design. For example, $10 will buy you a complete power amp kit based on a TDA2005 chip. That includes the PCB, all components and a heat sink. I built one as a power amp for a friend and the assembly was easier than most stomp boxes I've built. The TDA2005 can run from a +8V to +18V and can deiliver up to 20W RMS. I think the more interesting aspect of the project will be the preamp and any effects. I'm currently working on a preamp design that integrates one of the FV-1 DSP modules from OCT Distribution. The goal will be to have a super quiet clean preamp with a great set of tone controls and effects (reverb, chorus, tremolo, etc... ) This type of preamp could then be coupled to one of the many available power amp kits available (I will be using a parallel pair of LM3886 chipamp kits).

Of course, if you're not a fan of chipamps and really want to design and build a discrete power amp then my point is moot :) I'm all for doing things from scratch, but at least in my case $10 for a ready to assemble power amp was hard to ignore.

Here's a link to the $10 TDA2005 kit I was talking about: http://store.qkits.com/moreinfo.cfm/FK607

Hmm, you're right, I wasn't aware of that kit. Maybe the project is sunk... I'll think some more about it, but I definitely have no interest in competing with that kit as I can't beat that price.

http://store.qkits.com/moreinfo.cfm/FK604 (http://store.qkits.com/moreinfo.cfm/FK604) Same store, other kit, which does use tda2030, which might have nicer sound when clippin perhaps, perhaps not. When that ehx amp thread was on lounge, I thought about the specs that I dont need it, I already have tda7370  2x22 watts with 12 volt supply stereo chipamp, and the sound quality is very hi-fi, and it could be fit in pedal. Just too many goods to choose from.

http://www.thomann.de/fi/the_tamp_pm40c_endstufenmodul.htm (http://www.thomann.de/fi/the_tamp_pm40c_endstufenmodul.htm) Doin diy might not be cheaper than ready made these days. Does that module sound good with guitar... dunno because dont know what inside, and if I blow it, it is waste perhaps could I fix it or get it fixed...

Perhaps you should decide what size of speaker is optimum. I´m tired of my 8" practice amp and wat to go for 12 or 10.

- easy, reliable, low parts count, no exotic parts
- not another tired sounding practice amp but slight better the target

Keep in mind that the $10 kit is not designed for guitar. Line level input, no buffer, no eq, low impedance input.
I wouldn't worry about "competing" with it Taylor. It's not what you are shooting for anyway.

Quote from: Taylor on September 11, 2010, 11:10:08 PM
Hmm, you're right, I wasn't aware of that kit. Maybe the project is sunk... I'll think some more about it, but I definitely have no interest in competing with that kit as I can't beat that price.

Well, my goal wasn't to see you drop your project :( I was just trying to point out that perhaps the focus could be more on the preamp than the power amp side of things. The truth of the matter is that SS power amps are very commmon and easy to come by in kit form. The "standard" formula for an ss guitar amp is to generate all the distortion and other "tone shaping" in the preamp (or with stompboxes) and just feed that signal into a clean power amp circuit. The rule of thumb is to never let your power amp clip because it will sound horrible. Now, I am sure that a discrete SS power amp circuit could be designed to clip gracefully and in a musically useful way. If that is your goal then toss the chip amp idea and go for it!

However, I for one would love to see a great preamp that can be placed in front of an off-the-shelf power amp circuit to provide clean gain, reverb and some flexible EQ controls (let's face it, while stomp boxes can be great at providing overdriven and distorted sounds most of them have very crude, if any, tone control). And I know I can't just run out and buy a kit to do all of that like I can for a power amp. If you have a product/project that will get people a good preamp you won't have to compete against anyone. The closest thing I can think of is the preamp pcb from ESP and while it seems to be a good clean preamp thr pcb costs $18 and has no built-in effects like reverb.

Quote from: John Lyons on September 12, 2010, 12:27:43 AM
Keep in mind that the $10 kit is not designed for guitar. Line level input, no buffer, no eq, low impedance input.
I wouldn't worry about "competing" with it Taylor. It's not what you are shooting for anyway.

Thanks for pointing that out. As I said in my last post my point wasn't to say the project shouldn't happen, but that perhaps the power amp should be thought of as a COTS part rather than a major area for design efforts. I was not in any way suggesting that someone could simply buy that $10 power amp kit and have a working guitar amp. However, I can attest to it being quite suitable as a component in a guitar amp.
-matt

No problem Matt. I was just thinking that Taylor is building this from the ground up as a guitar amp
that anyone can build simply and that the $10 amp is not that (right out of the box at least).
Those little amps are cool but Taylor's going for something a lot more specialized.

Well, originally my plan really was to make a plain power amp, since that's what I want personally. I figured most people here rely largely on pedals to get their sound, so an amp that reproduces exactly what you give it, but louder, seemed useful. But I should probably rethink it as specifically being a guitar amp.

Quote from: armstrom on September 12, 2010, 12:30:20 AM
Now, I am sure that a discrete SS power amp circuit could be designed to clip gracefully and in a musically useful way. If that is your goal then toss the chip amp idea and go for it!

Of course it can! I have a late 60's Silvertone (Sears Canada, was made locally in Ontario, different than the American Silvertones) 10-watt  solid-state amp that distorts quite nicely.  A tube substitute, no, but a great amp for Garage Rock/Punk tones.  I think it only has 3 or 4 metal-can transistors too. If they could do it with 4 germ trannies in '68, I think we could probably cook something up.

As far as this fear of 120V (or are you guys talking 240V, because that's a whole different ballpark) goes, wiring up a transformer is two wires to the tranny, and one to the metal chassis. Perhaps that's oversimplifying, but if you can handle wiring a power amp, you can handle wall power. Just keep one hand in the pocket.

But if you'd rather not, laptop supplies might be a limiting factor, depending on how much power you want this thing to have.  Mine's only rated for 65W, if you can get this amp 70% effecient, that's 45W output.  Perhaps there are larger laptop supplies around, maybe 45W is plenty, I'm a little bit underwhelmed by my 25W bass amp when i REALLY wanna rock the basement. On guitar though, it's plenty loud.  Hopefully laptop supplies aren't noisy either, since they are switchmode.

/end rambling

Dave

I know AC wiring isn't  brain surgery, but it turns off a lot of people, and the idea with these projects is to get a lot of people interested to make the boards affordable. It's not that it's hard to do the AC wiring, but if you mess it up you could hurt yourself or start a fire. I think DIY should be a leisurely affair, not one with serious hazards, and many of the people who have built my PCBs are beginners at electronics.

We'd have to have about 10 times the power - 200 watts - to only twice as loud 20 watts, and at that power level it becomes a completely different project. So I think 20 watts is good enough. Adding another speaker will get you a lot more volume than just doubling or tripling the power.

Awesome project that you're tackling here Taylor !

As far as enclosures go, AX84.com has an amp enclosure design for folks that wraps around a 16X8X2 chassis.
They also have plans for a 1X12 cab.

http://ax84.com/corecabinets.html (http://ax84.com/corecabinets.html)

I did not use these plans, but I did build a head and 1x12 speaker cab once for an Ax84 P1Ex.
Probably the hardest part about working with wood, when you're a novice, is getting your hands on the right tools and learning how to use them correctly.
I am lucky enough to have a grandfather who really knows his way around woodworking and has a plethora of tools.

I'll post some pics so that you guys can get an idea, and what I built is by no means a beautiful boutique apparatus, but it has held together for several years now without issue and has even been gigged.

(http://i215.photobucket.com/albums/cc241/guyatron/IMG_0584-400.jpg)

(http://i215.photobucket.com/albums/cc241/guyatron/IMG_0583-400.jpg)

(http://i215.photobucket.com/albums/cc241/guyatron/IMG_0582-400.jpg)

(http://i215.photobucket.com/albums/cc241/guyatron/IMG_0581-400.jpg)

It's all hardware-store pine. The joints were all done with dowels. To make some of the side pieces, since the plank of pine was not wide enough, an additional piece was cut and then the two pieces were drilled, doweled, glued, and clamped to form the right sized piece.

The crazy stain pattern on the front was done by staining, sanding, staining, sanding ... etc etc, to make a quasi-burst effect.

With the right tools and someone who knows what the hell they're doing guiding you along the way, it's not all that difficult. But without the tools ... and an untrained hand wielding a circular saw, or working a table saw ... beware. I'm actually more fearful of screwing up with a saw than I am mains wiring.

Thunderbolt amps sells some reasonably priced raw cabinets. They also carry cut-to-length aluminum chassis http://www.thunderboltamps.com/cabs.html

The $79 head cabinet or $89 8" combo cab would probably be suitable for this project. Ignore the fact that he says its good for up to a 10W amp... he is thinking of the size limitations imposed by the iron needed for tube amps. A 100W SS amp could easily fit in that small head cabinet. It looks like it might even be possible to squeeze a 10" speaker into that combo cabinet with a new baffle.

Yeah, I'm thinking about emailing them and asking if they'd build the same combo amp with a hole for 10" instead. Hopefully for the same price.

Do you know if those thunderbolts come pre assembled or would I get to assemble it? What about their shipping prices?

Taylor: I don't think the power transformer will scare off as many people as you think. Perhaps adding a question about it to the poll, or having to a part of a new poll would be worth asking? After all, even if it's a bit dangerous, it doesn't scare me off. I bet enough people would support the project for it to be worth it. But even if you really don't want to, I'm still in. I would be more excited with a proper amp powersupply though, not a laptop supply.

So don't give up on this thing. I think this is different than the kit. In fact, I'd be willing to bet there's nothing like this project out there because those poweramps aren't designed with this kind of purpose in mind.

Jacob

I'm just not sure what would differentiate this from the dozens of solid state amp projects that have existed over the years, if it has the same power supply and everything.

What do you feel is the downside of the laptop power supply?

I think what's turning me off of the laptop supply is the unknown. I know the look and what amp transformers do. I have no idea what a Laptop supply looks like let alone where to get one or what it's like to use. After all, it's made to power a laptop, not a guitar amp. Wouldn't be better to use stuff that's made for guitars?

That's just my thought process. Maybe I need to get out of my box.

Jacob

im looking forward to building this (though my wifes not lol)

http://www.google.com/images?client=safari&rls=en&q=laptop%20power%20supply&oe=UTF-8&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1272&bih=887

A laptop power supply is just a power supply for a laptop computer. It looks like a plastic rectangle. As far as where to get them, I will take care of that if the project comes to fruition. Aron might carry a kit of the parts you can't get at Small Bear, since a lot of people, especially people outside the US, do not seem to like to buy from Mouser. I will make it really clear exactly what to buy, and make it as easy to get as I can. But because there are hundreds of millions of laptop computers out there, finding a suitable supply on ebay should be fairly easy.

There's nothing inherently laptop-y about these power supplies - they are just very affordable switch-mode power supplies which can provide a lot of current. Power supply filtering will happen on the PCB so it should be nice and clean.

I'm open to rethink the project according to what most people want, but the power supply is kind of the major thing for me, to make the project easy even for a complete beginner.

The laptop power suply sounds like a really good idea.
The TDA2030 is a 18 watt power amp, in a pentode package. Crate uses it still for their small ss combos.

Ok, freestyling now, but how about instead of designing an amp that maybe does or doesn't already exist....why not design a modular amp platform or protocol or something.

Like a motherboard type thing, with a built in power supply. And then we can all contribute plug-in or add-on daughter boards - power and pre amps, eq, effects, cab sims or whatever. You might even want to contribute some yourself  :icon_wink:  Should be fairly easy for people to modify existing layouts to suit.

I'd be happy to help out with mechanical design, which is my own area of so-called "expertise". And, of course, there are shedloads of proper experts around here to help and advise.

It could be a REAL collaborative effort but, more than that, it'll always be "Taylor's amp design". A man doesn't often get a shot at immorality.

Immortality, I meant.

But on the other hand....

guffaws at Mark I know I should say LOL or ROFL or something, but I'm not 12 so I wont.

As far as the power supply goes I think the laptop PS idea is a good one. Ultimately though I can't see that there's anything to stop people powering it with what ever they like, so long as it's up to the job. So if you're happy to deal with AC wiring and stuff then you can go down that route.

I'm rather late for the party, so what I would have suggested has already been put forward.

Recently I built an amp based on a TDA2050 powered by a laptop power supply (18V, 6A). As preamp I use a ROG Fetzer Valve. I also have a half built ROG Tonemender that I want to try as preamp.

It's really loud for basement use, but also very quiet, and I have no power filtering whatsoever.

It's pretty much based on a build by MartyMart, which again pretty much is by the data sheet:

http://www.diystompboxes.com/smfforum/index.php?topic=57018.0 (http://www.diystompboxes.com/smfforum/index.php?topic=57018.0)

Listen to Marty's sound sample

BTW: Ask your IT manager at work for a power supply. The PSU usually lives longer than the laptop so he may have a box of them lying around with no use.

It also helped to tell him that I was building amps for the company christmas party band :-)

Regards

Carsten

Quote from: slacker on September 12, 2010, 04:06:47 PM
guffaws at Mark I know I should say LOL or ROFL or something, but I'm not 12 so I wont.

As far as the power supply goes I think the laptop PS idea is a good one. Ultimately though I can't see that there's anything to stop people powering it with what ever they like, so long as it's up to the job. So if you're happy to deal with AC wiring and stuff then you can go down that route.

Right, that's true: if you want to add the trafo and rectifier it would be easy to do that.

Quote from: Taylor on September 12, 2010, 03:02:49 PMA laptop power supply is just a power supply for a laptop computer. It looks like a plastic rectangle. As far as where to get them, I will take care of that if the project comes to fruition. Aron might carry a kit of the parts you can't get at Small Bear, since a lot of people, especially people outside the US, do not seem to like to buy from Mouser. I will make it really clear exactly what to buy, and make it as easy to get as I can. But because there are hundreds of millions of laptop computers out there, finding a suitable supply on ebay should be fairly easy.

There's nothing inherently laptop-y about these power supplies - they are just very affordable switch-mode power supplies which can provide a lot of current. Power supply filtering will happen on the PCB so it should be nice and clean.

I'm open to rethink the project according to what most people want, but the power supply is kind of the major thing for me, to make the project easy even for a complete beginner.

Oh I see what you mean then. I'll have to think about it... I'm excited about the possibilities, because the small tube practice amp kit I'm looking at is 600 bones and I bet this can be done including cab and speaker for less than 200.

Jacob

Whats got me confused  ???
Is so many times I have read (hear and elsewhere) that switchmode supplies are a NO NO for audio use.
That even regulators and huge filter caps cant tame the spikes induced by the switching.
If this is indeed false,then yeah laptop supply all the way !!!!
I can buy them at the local thrift for 2-5$ all day long :icon_mrgreen:
Shoot I have several in my garage IIRC as well as a few old PSU from outdated PC's

I personally think and mentioned at the other forum that a clean pre-amp would be enough but to leave it so the end builder could add thier own OD channel,and of course the channel switching would be TiTs.
I would love it if I could replace the OD channel of my Crate with a Dr Boogie,Hmmmm  :icon_idea:
Ideally I would like one like Kirk Hammetts but with SS instead of tubes ,that is where you can pop in a module to get a new pre amp channel.
Make it so a Hammond 1590 B or BB would slide in from the front and BAM a new pre amp  :icon_eek:

Actually the crate GX20M I linked to does everything mentioned ,only the channel switching is done with a button on the chassis.
A footswitch option would be way better.
The spring reverb is grand and uses op amps,the OD is the Crate type and could be improved but the EQ and clean channel are excellent.
It uses the TDA 2040 chip and with a good efficient 12" spkr is quite loud and very nice in tone.
If you want I could take pics of the innards,I have used this amp for practice for at least 15 years now,so I would say its pretty dependable.
http://www.aronnelson.com/gallery/main.php/v/Brymus/Schematics/GX20M.pdf.html

The 10 watt Crate it replaced came with a "package" and the difference was like night and day tone wise.
The reason I kept it all these years.

I almost forgot a headphone out,so freakin useful.
I used mine for going line in to my PC for recording and it works great.(on the GX20M)
So yeah add a headphone out,maybe even an audio in and mixer knob for MP3s when practicing.

@ Jkokura
If you want a small tube practice amp save your 600$ and buy a Valve Jr for 150$,you can build a ton of different amps from it by just swapping a few caps and resistors.
It actually is like a DIY kit for building a lot of nice boutique amps,but its already a working amp.
If you can get a used EVJ half stack you wont be dissapointed.

Taylor, I would give the option on the PCB to use an external power supply or, for those with experience, an internal transformer/rectifier/etc, so it would suit more people.
I´d make a 20W or so amp, with gain, treb/mid/bass, and master. No channel switching, pre out/pwr in jacks. I don´t know how useful/feasible it would be to make it fit a stompbox enclosure...however big.
It should be clean with humbuckers at lo gain/high master, and have some dist at high gain/lo master. Never, never clip the power chip. No fan, just a heatsink, however big.
Regarding the power supply, are laptop ones bipolar? I´d make it bipolar power, to avoid a big cap at the output and pops/noises at power up/down. Are laptop PS´s fused?
Another option would be to use a desktop computer power supply, neat closed box, fan included, no mains wiring...

Just my opinions.

Quote from: Morocotopo on September 12, 2010, 05:04:04 PM
Regarding the power supply, are laptop ones bipolar?

No but some TDAs can be used unipolar so it shouldn't be a problem.

Here's another thought. Build something to use an ATX PC power supply. You get all sorts of useful voltages (+3.3V, +5V and a biploar +/-12 V) The +5 and +3.3 volt lines would be great for powering digital logic chips (the SSM2166 compressor, PT2399 or even the Belton BTDR-1H reverb module come to mind as they all require a regulated 5V source an FV-1 could make use of the 3.3V supply). The bipolar supply would have more than enough current to drive a properly designed op-amp preamp stage and the power amp too. You won't be able to use all of the available current most ATX power supplies can provide since a +/-12V swing won't get you huge power, but it would be more than enough for the projects we're talking about here. The bonus is that ATX power supplies are readily available and still remove the need to work with mains voltage. You can even find them small enough to fit inside an aluminum chassis without too much work. Here's a cheap example: http://www.datavis.com/StarTech-145-Watt-Micro-ATX-Power-Supply.html and you can buy the 24pin female connector for the PCB from sparkfun for $1.50. Sparkfun even sells a breakout board to convert an ATX supply into a bench supply for $15 http://www.sparkfun.com/commerce/product_info.php?products_id=9774

Edit: I should clarify, the -12V rail on most ATX power supplies can source less than 500mA on the -12V rail  vs 5A (and up!) for the +12V rail. The negative rail would be more than sufficient to power any bipolar preamp circuits but you would likely still be using a single power rail for any power amp.
-Matt

Quote from: armstrom on September 12, 2010, 05:40:04 PM
Here's another thought. Build something to use an ATX PC power supply. You get all sorts of useful voltages (+3.3V, +5V and a biploar +/-12 V) The +5 and +3.3 volt lines would be great for powering digital logic chips (the SSM2166 compressor, PT2399 or even the Belton BTDR-1H reverb module come to mind as they all require a regulated 5V source an FV-1 could make use of the 3.3V supply). The bipolar supply would have more than enough current to drive a properly designed op-amp preamp stage and the power amp too. You won't be able to use all of the available current most ATX power supplies can provide since a +/-12V swing won't get you huge power, but it would be more than enough for the projects we're talking about here.

^
Now here's an interesting idea!

I've got a micro-ATX supply just sitting around. I saved it just in cases some kind of project like this materialized.

Of course, using this kind of supply would make it really hard to use a tiny enclosure, but maybe the tradeoff is worth it?

Quote from: culturejam on September 12, 2010, 05:46:37 PM

Quote from: armstrom on September 12, 2010, 05:40:04 PM
Here's another thought. Build something to use an ATX PC power supply. You get all sorts of useful voltages (+3.3V, +5V and a biploar +/-12 V) The +5 and +3.3 volt lines would be great for powering digital logic chips (the SSM2166 compressor, PT2399 or even the Belton BTDR-1H reverb module come to mind as they all require a regulated 5V source an FV-1 could make use of the 3.3V supply). The bipolar supply would have more than enough current to drive a properly designed op-amp preamp stage and the power amp too. You won't be able to use all of the available current most ATX power supplies can provide since a +/-12V swing won't get you huge power, but it would be more than enough for the projects we're talking about here.

^
Now here's an interesting idea!

I've got a micro-ATX supply just sitting around. I saved it just in cases some kind of project like this materialized.

Of course, using this kind of supply would make it really hard to use a tiny enclosure, but maybe the tradeoff is worth it?

Yeah I have a couple old PC power supplies I bet alot of us do.
Plus the PT2399 projects have become pretty popular.

Quote from: Brymus on September 12, 2010, 06:08:53 PM
Yeah I have a couple old PC power supplies I bet alot of us do.
Plus the PT2399 projects have become pretty popular.

I'd rather leave the extra stuff (delay, etc) for people to do on their own. But I do think the PC power supply *could* be a great starting point for an SS amp.

And there was a project for an amp power supply using a laptop supply over at FSB.

I agree, I don't really see any utility in incorporating effects into this amp, since we all build effects anyway.

I think I'm going to stick with the laptop power supply. I know it probably seems like I'm being stubborn, but for simplicity, safety, ease of finding one, and small size, I think the laptop supply with a unipolar TDA chip is still the best way to go.

So, here's where it is right now:

- laptop power supply
- preamp
- 3-band EQ


Now, the question of switchable channels hasn't been decided as clearly on the poll. The majority do want switchable channels, but it's pretty close. I figured that most people on this board would use pedals as their "channels", but I guess not. Can I hear your thoughts, everybody, on why we should or should not have switchable channels?

I voted on the dual channels with separate EQs. I guess because I was thinking that it would be more useful to have two different full channels of amp emulation, like a fender clean and a marshall dirty. If you aren't going to have two full emulators, all you need do is have a footswitch that switches between two gain pots. That's easy enough to do as a mod and doesn't require any extra PCB space. Although, if you were to include it on the PCB, it would be easy to leave out.

Now that I type that out, What do you think Taylor of having that as an 'option' on the PCB. A second gain knob (channel) with switching as an Option, just like the Effects Loop or Reverb could be optional?

Jacob

nah dude ... laptop PS is a good idea

readily available and they can handle more than enough current

a buffered effects send/return (loop) would be a nice option to incorporate

Quote from: cab42 on September 12, 2010, 04:07:54 PM

BTW: Ask your IT manager at work for a power supply. The PSU usually lives longer than the laptop so he may have a box of them lying around with no use.

Unless they use Dell laptops... then you are usually left with a box of PSU's with broken plugs, and a box of laptops that still work, but have no power supply... not a problem if ya wanna wire in your own jack, tho!

Quote from: jkokura on September 12, 2010, 07:01:00 PM
I voted on the dual channels with separate EQs. I guess because I was thinking that it would be more useful to have two different full channels of amp emulation, like a fender clean and a marshall dirty. If you aren't going to have two full emulators, all you need do is have a footswitch that switches between two gain pots. That's easy enough to do as a mod and doesn't require any extra PCB space. Although, if you were to include it on the PCB, it would be easy to leave out.

Now that I type that out, What do you think Taylor of having that as an 'option' on the PCB. A second gain knob (channel) with switching as an Option, just like the Effects Loop or Reverb could be optional?

Jacob

Well, to have a footswitch would require a relay, or maybe electronic switching with a 4066 IC, otherwise you'd have your audio zooping through the footswitch cable, to the footswitch and back up the cable. So it does require the extra space for the relay and driver circuit. It's not a huge deal, but something to think about, as a lot of people who build their own pedals are suspicious of relays for some reason. Otherwise, I'd design all my DIY PCBs with relay true bypass, as that's how I do it with all my stuff. It adds an unfamiliar part which people don't seem to like. But again, not a huge deal.

Oh, unless you were going to build the footswitch into the amp's enclosure... somebody on the circuitworkshop thread linked a page or two back suggested that.

An optional second channel is a good idea, the key is just in making it simple to build either way. Often, when you add lots of "forked roads" where you can do things one of two ways, it really confuses people. So it's a tricky balance of making the project versatile but not really confusing to people with a little less understanding.

I think one channel is plenty. Switching from dirty to clean (the whole point of channels) should be as easy as bypassing whichever pedal is providing the dirt.

I also vote for a super-squeaky clean preamp so that it won't be overdriven by hot signals. If I want a nice JFET preamp to overdrive, I'll stick one in front of the amp in the form of a pedal. :)

Go with the laptop power supply.  :icon_cool:

Dang, you and I gotta have a talk and you explain Relays to me then Taylor. I've been trying to read up on them and see how to make them work for me for weeks!

Jacob

I'm really interested in seeing how you'll build this! I've got a similar but smaller amp powered by a 24V 1A SMPS. Still figuring out a suitable preamp...

Laptop power supply is a great idea, though. The one I'm using now (on my laptop) puts out 19V @ 4.7A... my friend's laptop "Mobile Animation Workstation" adaptor puts out a whopping 24V @ 6A 
:icon_eek:
144W?!?

Guessing most of it will go to waste... How are you gonna deal with heat? Mine's got a massive heatsink and its only 5W....

Quote from: culturejam on September 12, 2010, 07:46:05 PM
I think one channel is plenty. Switching from dirty to clean (the whole point of channels) should be as easy as bypassing whichever pedal is providing the dirt.

I also vote for a super-squeaky clean preamp so that it won't be overdriven by hot signals. If I want a nice JFET preamp to overdrive, I'll stick one in front of the amp in the form of a pedal. :)

This is what I figured most people would want, but the majority in the poll seem to want channel switching.

For those who want channel switching, tell me a little about why you'd prefer this over using pedals to switch from clean to dirty.

Quote from: Taylor on September 12, 2010, 08:42:04 PM
For those who want channel switching, tell me a little about why you'd prefer this over using pedals to switch from clean to dirty.

Yeah, I want to hear the reasoning behind this as well. I can't imagine why anyone would want a clean and dirty channel if they build their own dirt pedals.

I think this might be a case of "if you give people an option, they'll choose it".  :icon_lol:

hi..

here's my take on chip amps

:)

http://www.diystompboxes.com/smfforum/index.php?topic=86840.msg728338#msg728338 (http://www.diystompboxes.com/smfforum/index.php?topic=86840.msg728338#msg728338)

You could use a bridged amplifier configuration if you ultimately decide on a laptop PSU. Basically, two single supply amplifiers amplifying the same signal but inverted from each other. Connecting a speaker across the outputs negates the DC at Vcc/2 since the same potential relative to ground is at either end of the speaker, and results in only the AC output.

Plus , you get a larger output headroom. A typical single supply amplifier can only output a voltage that is around 1/2 Vcc because it uses the midway point as one connection to the speaker and the power amp output as the other - it can only go maximum peak 1/2Vcc negative and 1/2Vcc positive.

In a bridged amplifier, at the peak, one amplifier is going negative while the other goes positive. Each amp can go to 1/2 Vcc peak +/-, so when one goes up and one goes down that's actually the full Vcc across the speaker (peak).

Just be careful about the design, keep in mind that without decoupling (transformer/capacitor) you have Vcc/2 on the output of the amplifier that if shorted to ground may shut down the amp or cause disastrous damage... Ideally I would put decoupling on the output... but if you have the speaker in the same box as the amplifier, you can just hook up the speaker direct to the bridged outputs without much worry.

Channel switching would just be a convenience. This little guy should be pretty portable, sort of an all-in-one package, and having a few different choices in tone would make things simple. But a bomb three-band EQ design might make it unnecessary. With the title of "Forum Amp" it should easily impress, and I'm not sure a basic, clean amp is that impressive. Not that I'm not stoked to build this thing!  :icon_cool:

Taylor, I thought this would be more of an on the pedalboard kind of amp, where it would be easy to have a 3PDT to switch channels at your feet. No need for the signal to travel down a cord. If built into a head or combo cabinet, switching could simply be a 3PDT toggle switch on the amp.

I do want EQ though, so if the choice is channels or EQ, I vote EQ.

Jacob

I'm a total noob lurker here, but here's my take on this:

I like the idea of a "main configuration" with options to mod, replace, repurpose, etc. So, having a laptop supply as the nominal power source, with affordances for other options, is brilliant.

Likewise, having a preamp stage that could also feed a balanced line to a mixing board (and maybe a dedicated camcorder audio feed for youtube demos  ;)) would be great; having separate buffered instrument-level and line-level effects loops in the preamp would likewise be neat, if they could be optionally unused too. Being able to bypass the preamp with one's own DI-type pedal would be nice too.

I don't use a second amp channel because it tends to de-motivate me from moving around onstage. I prefer to use a Gigrig Loopy-2 in the pedal chain.  But if the dual channels were nominally identical and had separate tone controls, that would make it worth it, I guess. As a bass player I don't often go to a fuzz sound but I do sometimes need to fill a different tonal niche, and it's a pain to kneel down and dial in a second tone at the pedal board. In any case, if I can leave it out and/or populate it in later, all the better.

Which, having a bass-optimized parts list option would be awesome as well.

In any case, thanks Taylor!

Oh, ok then, nobody likes my idea about modularisation. Taylor, please don't let me be misunderstood.......let me try again:

How about semi-modular? 

A couple of people have (IIRC) mentioned how a TDA power stage plays nicely with a ROG pre amp. I've made a few with English Channel and Prof Tweed as preamp sections, and they've always been good enough.

So how about a power stage and physical package that is specifically optimised to work with ROG designs?  After all, the ROG designs are proven to be good, and it would take many many hours to design a pre for the Forum Amp that is any better.

If the masses decree so, it could also incorporate a switching arrangement to select between two (or more) of the preamps - you could switch between, say, Vox/Supro channels rather than just clean/mucky.

And if it could be made so that you can slide out/slot in the preamps to change flavours, that would be cool. Means we might need to change the for factor of the ROG circuits so that the inputs and outputs are in the same place (or maybe come up with a "pcb caddy" affair) but are we not men?

Quote from: markeebee on September 13, 2010, 03:11:31 AM
Oh, ok then, nobody likes my idea about modularisation. Taylor, please don't let me be misunderstood.......let me try again:

How about semi-modular? 

A couple of people have (IIRC) mentioned how a TDA power stage plays nicely with a ROG pre amp. I've made a few with English Channel and Prof Tweed as preamp sections, and they've always been good enough.

So how about a power stage and physical package that is specifically optimised to work with ROG designs?  After all, the ROG designs are proven to be good, and it would take many many hours to design a pre for the Forum Amp that is any better.

If the masses decree so, it could also incorporate a switching arrangement to select between two (or more) of the preamps - you could switch between, say, Vox/Supro channels rather than just clean/mucky.

And if it could be made so that you can slide out/slot in the preamps to change flavours, that would be cool. Means we might need to change the for factor of the ROG circuits so that the inputs and outputs are in the same place (or maybe come up with a "pcb caddy" affair) but are we not men?

It's not that I don't like the idea Mark - I like it a lot actually. It's just that, to me, a pedalboard kind of is a modular guitar processing system. So it seems like that kind of setup would largely be duplicating what people are already doing with their pedalboards. From the perspective of designing neat stuff, it's cool. When I was a kid, so like 2 or 3 years ago, I always built all of my LEGO, Capsela, Knex, etc. vehicles with little detachable mini-vehicles, docking stations, escape pods, etc. That's a lot of fun, and if you guys will buy it, I will have lots of fun designing it.  :)

But I'm thinking that that might not be adopted by enough people for it to work out.

Um, yeah, fair enough.  Can't argue with lego.

Having read back through the thread I see now that you've already addressed my idiot raving in previous posts, and I just misunderstood your initial brief.  :icon_redface:

Seems to me that what we're moving towards is something like a EHX Caliber, but at a close-to-ebay-chipamp cost?

  What does it do ?
 Where should we take it from there ?
 Is there something outside of the amplifier design we should be looking at ?
 *Does the final amplification stage do sufficiently well with bass and treble reproduction ?
 What happens with 'this' speaker and cabinet, room and surfaces ?  
   *this part of design can pretty well be nailed, any number of ways, has become extremely easier with use of a chip, but of course still requires 'a' power supply.
 Stereo ? Why not, if the power supply can handle the current draw [without a huge increase in cost], the second amp doesn't add that much cost and then doubles output @x voltage, allowing dual mono or stereo.
  I use a stereo chipamp unit it for MP3/Disc/recorder/playback of stereo recordings makes it pretty useful. I almost built a mixer for 2 into 1 playback.
  "doubles output"...ie requires a second speaker, so a doubling of power output is a bit closer to doubling of percieved loudness. A lot louder and louder with the sweetness is the best description I can offer, 2 speaker cones separated by X distance adds a slight touch of off-phasing effect.

Quote from: markeebee on September 13, 2010, 05:53:21 AM
Um, yeah, fair enough.  Can't argue with lego.

Having read back through the thread I see now that you've already addressed my idiot raving in previous posts, and I just misunderstood your initial brief.  :icon_redface:

Seems to me that what we're moving towards is something like a EHX Caliber, but at a close-to-ebay-chipamp cost?

Well, that's a class-D amp (the 44 magnum is no doubt a class-D)... quite complicated, quite a beast to design. This (non class D) would probably be much bigger... Unless you design around the loads of heat you are going to be dissipating into the enclosure. The EHX amps only manage to be small because of the ridiculous efficiency benefits that class D amps give you...

Knowing EHX's talent with dsp effects I would bet that those amps are designed around a custom programmed DSP chip to control the PWM conversion and switches.

I got the impression that this would be a medium sized to small amplifier, not "miniature".




A stereo chip amp would be nice for the bridged configuration I mentioned earlier.

So you guys who want channel switching...I assume you want a clean and dirty channel? (I can't see the use of having two clean channels.)

If so, that's definitely not something I'd want. I would much prefer to dial in my own dirt with pedals.

I really don't care about the preamp part. That should be easy enough for people to figure out on their own. So many JFet based preamp schematics around. But the power amp i'm really interested in. I've got a couple of TDA2030's and a 18V transformer, both from some sort of amp, i've never seen it complete, just a broken pcb and cut wires.

+! culturejam..

be nice to have a really clean 20w amp with a nice eq...bass/ mid (very scoopy)/ treb/ pres/ not overly bright though!....

then add our own flavour of dirt as one mans idea distortion is very different to anothers... :icon_twisted:

The channel switching question on the poll is almost tied.

What I think I might do as a compromise is to do a nice, clean preamp, with some switchable diode clipping in the feedback loop. This doesn't add much to the build in terms of parts, but gives you the ability to have a clean channel and simple overdrive channel if you want. Maybe you want a little stompbox amp in one package for taking to rehearsal or traveling. That would give you some versatility without going overboard with adding specific distortion circuits.

For those who want to build their own monster amp with switchable preamps, each with its own EQ, etc., this amp PCB would be a perfect building block, which you could marry to the preamps/overdrives/reverb of your choice. You could build a perfectly tailored amp to your tastes, and it would be much simpler to build than any other guitar amp project.

Bang on Taylor.

Jacob

Quote from: Taylor on September 13, 2010, 02:59:32 PM
The channel switching question on the poll is almost tied.

What I think I might do as a compromise is to do a nice, clean preamp, with some switchable diode clipping in the feedback loop. This doesn't add much to the build in terms of parts, but gives you the ability to have a clean channel and simple overdrive channel if you want.

This is exactly what I did with my TDA 1519b practice amp http://www.aronnelson.com/gallery/main.php/v/Brymus/TDA1519b_386AMP/
The problem I had doing that was,that the EQ and volume wasn't right when switching between OD and clean.
What I mean is that with the EQ set for good clean tones adding in the clipping diodes for the OD tones the EQ and volume had to be re-set for optimum sound.
Which is another reason I had the bass boost > more bass for clean less for OD,so then there was two switches...
It did however keep the part count lower and used less space.

This made me realize why so many prefer two channels each with its own EQ.
Same holds true for using pedals,if your TMB is set perfect for clean tone,when you engage whatever dirt pedal you use ,you are likely to need to re-EQ for optimum sound.
Then again this amp is just for practice not ,for mic'ing at a gig.
My problem is I want to practice what I am gonna play ,that means switching between clean and dirty in the middle of a song sometimes.
I guess it really comes down to what the intended use of the amp is to be.
Is it for just demo-ing pedals,or actually practicing for a show,ect,ect.

I think if you want a multi-channel amp with separate EQ for each channel, it would make a lot of sense to use this amp as your power amp and pair it with your 2 (or 3) favorite preamp pedals with their own EQ. Let's say we made this amp with a Fender-ish preamp channel and a Marshall-ish channel. Then everybody who doesn't like those preamps would be annoyed that these choices were forced on them.

If we keep it simple, make the preamp and 3-band EQ bypassable, then you can build it specifically to suit your needs by adding preamps/overdrives that you prefer, without forcing those choices on everyone building the PCB.

Taylor, i can't wait to see a finished product for this amp, i love your idea for just using preamp pedals for preamps, plus that way it'll be easy to put a tube preamp in front of this thing, I'm definitely interested in this amp, i'm hoping this thing will have some mods to make it more bass friendly

I'm a bass player, so I will definitely make sure this does well in that application. Although, a lot depends on your speaker(s) of course - you can't expect deep bass coming out of a single 8" speaker for example.

i do have some unused 15" PA speakers laying around....I think those ought to be handle a little bass

Yep, although don't get too caught up in stereotypes about speaker size, because there a lot of other factors that matter about as much. If you want to build really, really good bass cabinets, check out billfitzmaurice.com. His designs are mostly horn-loaded, which gives amazing efficiency (so you'll get way more volume out of this amp than with a standard speaker cab), great deep bass, way better dispersion than standard cabs, etc. They are a little more complex to build than a plain box, but vastly superior.


So, based on my current plan for this amp, it will be ideal for the following applications:

-Build it as a simple, standalone amp stompbox. Just build it by itself into a stompbox, with overdrive and EQ on their own stomp switches. Plug from this box into a speaker. Great for practice, travel, simple applications, but honestly 20 watts for guitar should be enough for small gigs as well.

-Use it as a power amp building block. Build your dream custom amp by combining switchable preamps/overdrive circuits with their own EQ, and running it all into this power amp. The amp PCB itself will be small enough that you can cram a lot of other stuff into an amp-size enclosure, even tube preamps.

-Build it into a guitar combo. I will include lots of information on building simple guitar combos in my PDF document, so if you want to build a nice combo amp for testing pedals, practice, etc., there will be enough info to get you going.

Quote from: Taylor on September 14, 2010, 04:28:55 PM

-Build it as a simple, standalone amp stompbox. Just build it by itself into a stompbox, with overdrive and EQ on their own stomp switches. Plug from this box into a speaker. Great for practice, travel, simple applications, but honestly 20 watts for guitar should be enough for small gigs as well.

-Use it as a power amp building block. Build your dream custom amp by combining switchable preamps/overdrive circuits with their own EQ, and running it all into this power amp. The amp PCB itself will be small enough that you can cram a lot of other stuff into an amp-size enclosure, even tube preamps.

Taylor, one thing I didn't think of when building a small amp was powering up the separate preamp. If you're gonna go for a modular design, you can also consider adding a power jack to power up other components. Saves a whole jack/adaptor/plug socket/battery/whatever people use to power their fx

Just my $0.02  (And headache to finish that amp!)

Yep, that's a good idea, I will probably add that.

Quote from: phector2004 on September 15, 2010, 12:38:16 AM
Taylor, one thing I didn't think of when building a small amp was powering up the separate preamp. If you're gonna go for a modular design, you can also consider adding a power jack to power up other components. Saves a whole jack/adaptor/plug socket/battery/whatever people use to power their fx

Just my $0.02  (And headache to finish that amp!)

That could be as simple as leaving extra pads on the PCB for all the various (filtered? regulated?) voltages.

About the power supply... If the idea is to use an external laptop PS, then you probably want an onboard voltage regulator - both to smooth out the input voltage (as some would be switching supplies), and also to accomodate the range of voltages (12 - 20+ depending on the laptop it was intended for).  Because chipamps can draw quite a bit of current, the usual VR suspects are a little light-weight.  LM78XX are rated for 1A, and LM317 are rated for 1.5 amp.  I would suggest a beefier VR - like the LM338 (rated for 5A), or at least the lm350 (rated for 3A IIRC).  These are available in TO-220 packages, so they don't take up too much space, and will save builders a lot of grief when it comes to chipamps that are a little snippy about their power supplies.  Important tip: plan to add an appropriate heatsink, and don't plan to use the enclosure for it, as the heatsink tab on these is connected to the output (not ground).

About the signal input - consider using a pot/trimmer to scale the input to the chipamp - to allow flexibility in the offboard preamp.  Overdriving chipamps usually causes nasty-sounding distortion (or even lets the smoke out of them).

Excellent advice, thanks.

I would suggest the opposite, actually.  You would be very hard pressed to find an unregulated laptop PSU, so the only thing you might have to worry about is residual high frequency ripple.  That can be taken care of with a relatively small choke and filter cap.  Adding a linear regulator is going to increase the thermal load that has to be dissipated by the enclosure, which is still an unknown quantity at this point.

Quote from: earthtonesaudio on September 15, 2010, 01:30:49 PM
I would suggest the opposite, actually.  You would be very hard pressed to find an unregulated laptop PSU, so the only thing you might have to worry about is residual high frequency ripple.  That can be taken care of with a relatively small choke and filter cap.  Adding a linear regulator is going to increase the thermal load that has to be dissipated by the enclosure, which is still an unknown quantity at this point.

Agreed, linear regulators are not built to handle high frequency ripple, rather 60Hz... I doubt they will be very useful at ripple speeds from 400kHz to 2mHz. Laptop PSUs are all "regulated" to different degrees of success. The basic operation of any SMPS requires feedback from the output to the input to keep the output stable and thus has regulation.  

A reactive filter is an excellent suggestion.


Thermal  dissipation is a problem you need to focus on, I think... Since you want it to be able to fit in a stompbox enclosure and be around 20 watts. Like I said, the EHX amps are possible because they are Class-D and very efficient, minimizing the temperature of the box.

Quote from: JKowalski on September 15, 2010, 01:46:05 PMThermal  dissipation is a problem you need to focus on, I think...

Yes, for sure. I'm not aiming to fit it in a b-size box like the EHX amps, so I will be doing lots of experimenting with heatsinking to find an ideal solution.

I'll build this in nothing smaller than a BB. The new Smallbear 125BB's sound like a good idea for this. I likely will build it into a 1590DD though, mostly because i want additional options.

Jacob

Yeah, a 1590D or DD is about what I was thinking. The board will probably fit in something smaller, and if you wanted to get creative with machining the enclosure to accommodate the heatsink, it could maybe work in a 1590bb or the 125bb as you say.

Since has passed 2 years from trying to build a combo...and i'm still unsuccesful..I appreciate your work for the forum Taylor!!! ;D ;D ;D
It's exactly what most of us need..as player i suggest the possibility to plug headphones... sometimes the neighbours..you know :icon_lol:
but also can be used before playing while other bands are rocking ;)

Ric

I was planning on building mine with an optional headphone amp after the preamp also. This is the kind of thing that is an add on I think, because the main focus of the project is getting an easy to build solid state power amp going for us. Lots of preamps out there, not so many easy to use guitar focused power amps. A headphone amp defeats the use of a power amp.

So if you want to add one on with a kill switch for the power amp, I'm sure I will do it as well, so somebody if not me will add details to the 'build your own forum amp' thread that will exist after the PCB has been made.

Also, If you want some people to be guinea pigs, count me in Taylor.

Jacob

No offense meant to anyone, especially Taylor,just my humble opinion but...
Personally ,I was hoping for more than just another chip amp PCB.  :icon_cry:

After all there are entire websites devoted to chip amps as a power amp. As an example these people have been doing it for years.
http://www.chipamp.com/ (http://www.chipamp.com/)

The web has literally hundreds if not thousands of chip amps as a generic power amp designs and PCB transfers.
Even the data sheets to alot of the TDA chip amps include recommended PCB transfers.
As an example the TDA 2030 was mentioned : http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1458.pdf (http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1458.pdf)
Figure 14 from the data sheet IS an already designed and tested to be stable PCB transfer.
Ready for the masses to add their own preamp,and whatever else.

That was a very good idea having the poll/ballot but I am very suprised at the end result.
So if the majority want another chip amp/power amp with the rest left for them to design/add.
Then by all means give them what they want.
To me it sounds like your just going to end up with a 20 watt "gainclone" running off a laptop supply instead of the recommended transformer.

Still I am all for any project that will help Aron/the forum and the store.
So carry on ,and cheers to the success of the "Forum Amp" .

I do see what your offering: A  compact 20watt power amp without the need for mains wiring, a PCB ,and detailed instructions in PDF form.
EDIT-spelling

None taken. It's the simple truth that you can't please everybody, so my job when putting these projects together is to balance out the various opinions and come to a single conclusion. That necessarily means that it can't be perfect for everybody. For example, I'm including a preamp, with switchable clipping, and a 3-band EQ. For you, I guess this is not enough. But for others, it's too much! Whaddaya gonna do?

Thats cool,I thought the preamp was to be whatever pedals we use.
So I like that your are adding the preamp and TMB,that is a big plus. :icon_cool:

And yes ,I am bummed no channel switching  >:(
That would have made it worth my time to build and learn from.
For me I have enough amps that rely on pedals for channel switching.
I dont have a DIY amp that does it on it's own.

But like you said,what are ya gonna do...

Glad I could express my opinoin with out offending you.  8)

how about a charge controller to connect rechargeable battery's to alternative energy sources, cigarette lighter or wall as an option or with it in mind.?

guess it could be done separate.
http://www.solorb.com/elect/solarcirc/lvd1/index.html
AA Battery Solar Charger
http://www.solorb.com/elect/solarcirc/aacharge/index.html

stumbled upon this site about building a portable video device it has info and pcbs of amp and preamp projects :
http://translate.google.com/translate?hl=en&sl=es&u=http://www.construyasuvideorockola.com/&ei=nWWRTIbTIYK78gbOy5igBg&sa=X&oi=translate&ct=result&resnum=1&ved=0CBUQ7gEwAA&prev=/search%3Fq%3Dwww.construyasuvideorockola.com%26hl%3Den%26client%3Dfirefox-a%26hs%3D862%26rls%3Dorg.mozilla:en-US:official%26prmd%3Div
PDF:
http://www.construyasuvideorockola.com/downloads/tda2050.pdf

plug and play DLNA?
network playback?
http://wiki.xbmc.org/index.php?title=UPnP_Sharing
http://free-electrons.com/pub/video/2008/elce/elce2008-scholz-coherence.ogv

usb stick playback?
http://dspdap.sourceforge.net/building.html
http://www.frankvh.com/mp3-player.html

I just want to chime in and say Taylor I think you are doing a fair job with coming up with these decisions and I look forward to building one. The general idea fits very well with my personal interest in building amps. Kudos on not including mains power in the project as my last two experiences with electrocution weren't that cool  :icon_mrgreen:

I personally probably won't build the diode clipping section in to mine, but it will be easy enough to omit, so no real issue there. I think you are doing a good job of leaving it open and flexible enough to be useful to a lot of builders.

Yeah I think its a good project.
I misunderstood,in that I thought it was just a power amp that you had to plug your pedals into as preamps.
I just didnt see the appeal of that.
But a simple complete guitar amp with a TMB tonestack sounds like it should appeal to alot of people.

Quote from: Top Top on September 15, 2010, 09:47:52 PM
I just want to chime in and say Taylor I think you are doing a fair job with coming up with these decisions and I look forward to building one. The general idea fits very well with my personal interest in building amps. Kudos on not including mains power in the project as my last two experiences with electrocution weren't that cool  :icon_mrgreen:

I personally probably won't build the diode clipping section in to mine, but it will be easy enough to omit, so no real issue there. I think you are doing a good job of leaving it open and flexible enough to be useful to a lot of builders.

Thanks for the encouragement.  :) Listening to your album right now, actually. I'll really be looking forward to seeing your build, as I think you have a cool aesthetic going. Where are you in the country, BTW? Just curious if there's any chance I could see a show.

I think it's a solid feature set I've decided on, which provides a nice little niche. As I said, it can't be all things to everybody but I think it's good, and I know I'll build several of them, to have around for different purposes.

So now the difficulty turns to the implementation, making sure things don't overheat/melt/explode/kill your speakers, etc. I see some serious datasheet studying in my future.

Quote from: Taylor on September 15, 2010, 11:54:42 PM

Thanks for the encouragement.  :) Listening to your album right now, actually. I'll really be looking forward to seeing your build, as I think you have a cool aesthetic going. Where are you in the country, BTW? Just curious if there's any chance I could see a show.

I think it's a solid feature set I've decided on, which provides a nice little niche. As I said, it can't be all things to everybody but I think it's good, and I know I'll build several of them, to have around for different purposes.

So now the difficulty turns to the implementation, making sure things don't overheat/melt/explode/kill your speakers, etc. I see some serious datasheet studying in my future.

I'm in California... though I'd like to make it pretty much everywhere again one of these days...

I have looked at datasheets for a fair number of the amp chips and dissected several power amps that use them (mostly in general car audio or home stereo type applications). Generally they seem to be designed to be implemented pretty simply, like just a handful of caps and resistors. The most important thing seems to be that big finny chunk of aluminum attached to the chip  :icon_mrgreen:

Come on...the Randall RG100ES preamp section with a lower wattage power amp.

Apologies if this has been said I haven't read the whole thread and in a hurry, but I think maybe it would be a good idea to include instructions on how to mod you PCB or add all the other things people are asking for, like channel switching and such. Or even if you make a basic platform for people to mod on to. We could have a forum with suggestions and instructions covering everyone's needs.

Quote from: Hupla on September 16, 2010, 10:45:06 AM
Apologies if this has been said I haven't read the whole thread and in a hurry, but I think maybe it would be a good idea to include instructions on how to mod you PCB or add all the other things people are asking for, like channel switching and such. Or even if you make a basic platform for people to mod on to. We could have a forum with suggestions and instructions covering everyone's needs.

Yep, if you've seen my other PCB projects, you can see that I always include extensive information on modifying them in the PDF document that accompanies the PCB. So I will definitely cover as much as I can, although this is a bit more open-ended than building a stompbox, so there' no way I can do it all in one document. Having a separate forum for it is an interesting idea - if it really takes off I will talk to Aron about that.

Hey Taylor,

I fired up my wall-wart powered chip amp, cranked the volume up from 'bedroom' to 'basement', and noticed something strange... it hums whenever I touch anything in the signal pathway, whether it's jacks, plugs, cables, or even the guitar itself (strings, bridge, pickups, tuners, etc). I remember seeing a safety video somewhere where the same thing happened with a store bought amp when people cut off the grounding prong from their power cords... think it was posted on this forum, don't remember what exactly was causing it to hum.

I have a gut feeling my amp buzzing may be related to my 2-prong power supply (although it seems weird to me that it should even matter, cause normally the ground prong shouldn't be doing anything  ???)

Do you think something similar could affect the Forum Amp?
Does anybody know if there's anything concerning this to consider that may not have been implemented in my amp?

Well when you touch anything in the signal path, you're basically a big antenna for hum.  Even a grounded amp would do that.

Quote from: jkokura on September 12, 2010, 02:12:11 PM
I think what's turning me off of the laptop supply is the unknown. I know the look and what amp transformers do. I have no idea what a Laptop supply looks like let alone where to get one or what it's like to use. After all, it's made to power a laptop, not a guitar amp. Wouldn't be better to use stuff that's made for guitars?

That's just my thought process. Maybe I need to get out of my box.

Jacob

A laptop supply is just like a wallwart, but with higher amperage output, generally. They are also a dime a dozen.

It's my guess that these two reasons are why Taylor has chosen that type of power supply.

Edit: I thought the above comment was made at the end of the thread (recently), but somehow I missed the fact that it was from 10 days ago  :icon_redface:

Taylor, by the way, I just bought some TDA2005 chips today. I am going to start with the datasheet schem and see what I can tack on the front to make it more guitar friendly. If I beat you to it and come up with anything useful, I will certainly share what I've got with you.  :icon_mrgreen:

For my attempt, I will probably build a really simple preamp myself though, maybe not much more EQ other than switchable input caps. I still don't think your plan is a bad one and I think that like the ruby has made it easier to gear the 386 to guitar players looking for some home jammin' this idea could be a step up from that and make it easy to get into something a little louder without a lot of complication or expense.

I haven't read this whole thread but these guys (http://store.qkits.com/category.cfm/AUDIO) sell SS power amp kits for less than it would cost me to even think about a design, let alone coming up with a PCB for it. I would go the kit route for the power amp and then have fun coming up with a preamp (or not- just plug pedals into it or etc...).

QuoteI have a gut feeling my amp buzzing may be related to my 2-prong power supply (although it seems weird to me that it should even matter, cause normally the ground prong shouldn't be doing anything  Huh)

Actually it is doing something, but not like what you're thinking.  It's grounded to the chassis which is a huge shield for your circuit.  And guess where your guitar string ground ends up after it goes through the cable/preamp/etc - the chassis ground.  Somewhere your circuit needs to be Earthed, for safety and noise reasons. 

What about making a simple single ended tube amp? That would be much better and it would probably sound amazing :)

Quote from: Kitarist on September 23, 2010, 03:53:53 PM
What about making a simple single ended tube amp? That would be much better and it would probably sound amazing :)

That's a fine idea, but totally different from the concept of this. Check out the Firefly if that's what you're looking to build - no point in redesigning that, especially since I'm not a tube guy and would have no idea how to do so.

Quote from: DougH on September 23, 2010, 08:55:56 AM
I haven't read this whole thread but these guys (http://store.qkits.com/category.cfm/AUDIO) sell SS power amp kits for less than it would cost me to even think about a design, let alone coming up with a PCB for it. I would go the kit route for the power amp and then have fun coming up with a preamp (or not- just plug pedals into it or etc...).

Yep, somebody posted that a few pages back, and it has definitely given me pause about whether to continue with the project, especially given all of the dissent about what the project should be. I thought it would be cool, but I'm not sure now if enough other people agree to make it worthwhile.

I think it would be cool!

Quote from: defaced on September 23, 2010, 10:08:50 AM

QuoteI have a gut feeling my amp buzzing may be related to my 2-prong power supply (although it seems weird to me that it should even matter, cause normally the ground prong shouldn't be doing anything  Huh)

Actually it is doing something, but not like what you're thinking.  It's grounded to the chassis which is a huge shield for your circuit.  And guess where your guitar string ground ends up after it goes through the cable/preamp/etc - the chassis ground.  Somewhere your circuit needs to be Earthed, for safety and noise reasons. 

hmmm well its just a populated + wired circuit board as of now, with +24V DC and Ground connections... No mains voltage, transformers, or filter caps to worry about, but I figure whatever (I / the board designer) did wrong should be looked into. For new builders not to lose sleep over, at least.

I don't mean to hijack this thread, but the buzz slightly spoils an otherwise perfectly working amp  :-[

Taylor whatever you do, just make sure it is more elegant than this:

(http://oi54.tinypic.com/11ahj0y.jpg)

Quote from: Taylor on September 23, 2010, 04:13:12 PM

Quote from: DougH on September 23, 2010, 08:55:56 AM
I haven't read this whole thread but these guys (http://store.qkits.com/category.cfm/AUDIO) sell SS power amp kits for less than it would cost me to even think about a design, let alone coming up with a PCB for it. I would go the kit route for the power amp and then have fun coming up with a preamp (or not- just plug pedals into it or etc...).

Yep, somebody posted that a few pages back, and it has definitely given me pause about whether to continue with the project, especially given all of the dissent about what the project should be. I thought it would be cool, but I'm not sure now if enough other people agree to make it worthwhile.

Getting everyone on this forum to agree on anything is like herding cats. IOW- it won't happen. I wouldn't necessarily give up on your idea though. Given that there are so many kits available for SS power amps like this, it might make part of this project a lot easier. Using the XYZ power amp kit you could adapt it by adding a limiter circuit to the preamp, etc. And of course you need to figure out your preamp, tone controls, etc anyway. Unless there is something you are trying to do that is not available in an inexpensive kit form, it may make sense to build your project around an existing piece of hardware. No sense in re-inventing the wheel, IMO.

Quote from: DougH on September 24, 2010, 08:50:10 AM
Getting everyone on this forum to agree on anything is like herding cats. IOW- it won't happen.

It can be done, but it helps to have a well-defined path for them and a skilled cat-herder (like my wife).  :icon_wink:

(http://runoffgroove.com/herdingcats.jpg)

I planned to dive in black art of makin solid state guitar amp anyway so decided if I build a combo case first so perhaps that pushes and forces me to build it ready, have few chipamps ready and some transformers and more than enough speakers. Went to lumber yard I had find good plywood some year ago, new owner and same import junk that everybody has and not right thickness

Sometimes you can see a spiffy pcb design, such that you can cut/saw it in two or more parts, like power and pre amp and just use what you need, or populate it all

I think making one that is small enough ( like the noisey cricket etc.) to fit in a guitar case compartment and loud enough to use at a reasonable gig volume ( 20 watts ) with a small walwart style power supply and a simple preamp with mid bass treble and fx loop and enough umf to break up just a touch would still be a sweet forum amp and worth developing for sure. Everyone likes the idea and the principal and they will all tweak it to their own taste anyway. its half the fun and it would be a nice back up to have on hand when your tubes go out at a gig and you left the spare parts bag 100 miles away. Does anyone on this forum play without an overdrive or distortion pedal....really..?

Yeah, that's basically my approach. Don't worry, it'll happen. Some days I get a little pessimistic about things in general, but I think it's a useful project and I'm working on it right now.

Quote from: Top Top on September 24, 2010, 04:02:01 AM
Taylor whatever you do, just make sure it is more elegant than this:

(http://oi54.tinypic.com/11ahj0y.jpg)

Well, I'm not sure I can beat that unless I can get my fab house to do a custom argyle-pattern soldermask.

  Here's the how I used:
  Cut off the chips unused legs.
  Install the chip across perfchunk, diagonally [some slight lead bending required].
  Bind 3 capacitor-barrels with strapping to form a triangle, drop a screw down the center, make sure the screw has threads that are tight-turning so they lock, adjust the screw so the 3 'feet' and the screw pin-down forms a solid platform.
  That turns the 3 heavy-large-floating items into a solid place to work from.
  The rest of the circuit is either hanging garden, soldered to copper pads or on the chipleads atop the little perfchunk.
  The legs of the heat-sink-mounted chip holds the perfchunk, thick wires stabilize the 'floating' end.

            C   h   I   P
l HEAT  SINK   /Perf/  Filter-Lugs
l Block-table        3 Filter Capacitors
l------------------------------------------------chassis

  The caps and heatsink are a solid-form ie in a chassis or on a board, so the little bits inbetween and everything is stable.
  PCB is only 11 or 14 buxx? and the kits are bulk...maybe a slight cost decrease to buying the kit ?
  I did it this way because I had the chips/caps and most of the 'etceteras' handy already.
 

I am just posting this because its in the spirit of this project. The amp is just a power amp only. No volume knob or anything, just an input jack. Tube pre ( i know you dont want to mess with those ) . I am surprised at how LOUD and punchy this thing is. It sounds good with solid state preamps as well like a tube screamer. 3 watts is hecka loud......anyway....the tda7267a seems to work well at 9volts and there are only 7 or 8 parts to the amp...for what its worth.   http://www.youtube.com/watch?v=T-sNT_xjJ9E

I just built up the first prototype, on perf board. Currently I'm using an opamp buffer, into the TDA7240a-based amp, using a 19.5v power supply, regulated down to around 14v with an LM338. Huge thanks to waltk for his suggestions so far.

This amp sounds great! It really couldn't be simpler, and yet it puts out really nice, clean low end, and very rich and natural mids and highs. I am currently playing bass into it, but I will be testing it with guitar and keyboards soon. For guitar, this thing is going to be loud. Even for bass, where our old nemeses  Fletcher and Munson (http://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves) have stacked the deck against us in the relationship between frequency and loudness, this is a totally usable amp. I'm plugged into an EVM 15L 15" cabinet, but pairing 2 of these amps (which would still be quite simple and small) with 2 speaker cabinets would easily keep up with a drummer when used with a bass. For guitar, one of these should be enough to be irritatingly loud.

I mean, I know it should be no revelation that this kind of thing puts out nice, clean power across a full range of frequencies, but having used cheap solid state amps in the past and finding them to sound terrible, I wasn't sure what to expect.

What I have going on right now has fewer parts than a Tube Screamer.  ;D Even once I add an optional clipping stage in the preamp, and 3-band EQ, this should be comparable to a stompbox in terms of build complexity.

Thermal dissipation does not seem to be too difficult. I am currently using two 125b enclosures for the heatsinks - one for the regulator, one for the power amp chip. They did not get particularly warm, and this is with no thermal paste. More intense and prolonged usage will no doubt heat them up more, and I always prefer to err on the side of overkill w.r.t. safety, but that said, I think it should be very possible to build this into a fairly small enclosure, and use the enclosure as the heat sink. Some tricky mechanical issues to be dealt with there, in terms of mounting the chips and the pots, but nothing I can't sort out.


The one real bummer is that the LM338's heat sink tab is not tied to ground, but to V_out. Why the F did they do that!?  ::) So that means that a mica spacer or similar, to conduct thermally but not electrically, will be needed when mounting that tab to the heat sink/enclosure.

The good thing about low powered amps is that the human ear response works for you because you don't need massive power to get up to too loud for bedrooms.

Speakers are (almost all) rated in sound pressure level at 1W drive. For guitar speakers this is in the range of 94db to 108db at 1W of drive. This is LOUD if you're not trying to be heard over a band or an audience. A 10W amp is just noticeably louder than a 1W, and it takes 100W (roughly) to be subjectively twice as loud as a 1W. As long as the 1W amp is NEVER clipping and doing ugly solid state artifacts on its own, the sound should be good if the preamp is a distortion/limiting device on its own and the speaker is a guitar type speaker for the final filtering it gives.

The acme* of this apoproach is the Thomas Organ Vox amps and UK Vox Supreme/Conqueror/Defiant, which IMHO are the best sounding solid state amps ever made. Others may have other opinions.

*Acme (pronounced /ˈækmiː/; from Greek: ακμή, the peak, zenith, prime) denotes the best of something.

I tried my pentode driver with this (http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=43811&g2_serialNumber=1) the other day and it sounded fantastic. It could get very LOUD too but didn't have to in order to sound good. One of the nice things about this setup is the pentode driver has 30V p-p available in the power supply and the power amp is a 50V circuit. So the pedal could never overdrive the input of the power amp. Turning the output level of it up all the way just made it loud and clear. I think there's a lot to be said for pairing a good sounding "distortion engine" with a SS power stage. The only caveat I can think of is that (in this case anyway) sometimes we have to roll off the highs in the pedal to deal with a typical guitar amp preamp. With the power amp you don't need that, and this setup was slightly dark. (I thought it might be an impedance issue, but I tried buffering it which didn't help.) I'm going to disconnect the LPF in the pedal and see how that sounds. This is a great approach though, IMO.

Hi all
interesting ideas +1 for RG's comments, especially about speaker efficiency.  Any speaker with ok bass response and about 100dB/W will sound very big.  Probably need to be at least 8 inch with a v good magnet.  My 18 watter had a single Calestion Heritage and it sounded like a 747 landing  :icon_evil:.

QuoteAs long as the 1W amp is NEVER clipping and doing ugly solid state artifacts on its own....

What about using a small (approx 1W) output transformer (ie push-pull Class AB - and you can add negative feedback if you want to clean it up even more).  This filters high-frequency nasties and takes away any advantage from extra volume (it doesn't get any louder because it saturates).  

Two examples of the push-pull tranformer approach are the Pignose 9 volter (approx 3W), and the "Deacy"/Mullard/shelf radio amps (about 1W).  My personal opionion is that these are outstanding amps.  Like RG suggests, it would be good to start with a classic amp that sounds great.  Then update and mod it for low noise, effects loops, alternate pre-amps, etc.  Recently, a correct version of the Pignose schematic finally appeared on the web, and was referenced in the forum.
cheers

Quote from: Taylor on October 12, 2010, 04:00:37 PM
I just built up the first prototype, on perf board. Currently I'm using an opamp buffer, into the TDA7240a-based amp, using a 19.5v power supply, regulated down to around 14v with an LM338. Huge thanks to waltk for his suggestions so far.

This amp sounds great! It really couldn't be simpler, and yet it puts out really nice, clean low end, and very rich and natural mids and highs. I am currently playing bass into it, but I will be testing it with guitar and keyboards soon. For guitar, this thing is going to be loud. Even for bass, where our old nemeses  Fletcher and Munson (http://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves) have stacked the deck against us in the relationship between frequency and loudness, this is a totally usable amp. I'm plugged into an EVM 15L 15" cabinet, but pairing 2 of these amps (which would still be quite simple and small) with 2 speaker cabinets would easily keep up with a drummer when used with a bass. For guitar, one of these should be enough to be irritatingly loud.

I mean, I know it should be no revelation that this kind of thing puts out nice, clean power across a full range of frequencies, but having used cheap solid state amps in the past and finding them to sound terrible, I wasn't sure what to expect.

What I have going on right now has fewer parts than a Tube Screamer.  ;D Even once I add an optional clipping stage in the preamp, and 3-band EQ, this should be comparable to a stompbox in terms of build complexity.

Thermal dissipation does not seem to be too difficult. I am currently using two 125b enclosures for the heatsinks - one for the regulator, one for the power amp chip. They did not get particularly warm, and this is with no thermal paste. More intense and prolonged usage will no doubt heat them up more, and I always prefer to err on the side of overkill w.r.t. safety, but that said, I think it should be very possible to build this into a fairly small enclosure, and use the enclosure as the heat sink. Some tricky mechanical issues to be dealt with there, in terms of mounting the chips and the pots, but nothing I can't sort out.


The one real bummer is that the LM338's heat sink tab is not tied to ground, but to V_out. Why the F did they do that!?  ::) So that means that a mica spacer or similar, to conduct thermally but not electrically, will be needed when mounting that tab to the heat sink/enclosure.

I still think the regulator is a needless waste of space & power. It probably isn't helping much as far as filtering out HF ripple, and even if it was a simple reactive filter would do it better & wouldn't dissipate the heat which is definitely something to minimize. From what I have seen nearly all laptop supplies are 19.5 volts or very close anyways, so I don't think universality is a problem.

The regulator is there to drop 19.5v to a safer voltage, not for filtering. The amp chip cannot take over 18v, and I don't think it's wise to hit it with the max voltage it can handle. What would you suggest instead of a regulator for dropping 19.5v down to 14 or 16v?

Not so much a derail as a small kink in the track.....

When you push a chip amp into overload, it never sounds quite right to me.  It's never mushy enough.  Always sounds like a sore throat.  So I was thinking about non-linearity and compression, and other nice stuff that happens in a valve output stage, and I found this (apologies if it's old news):

http://www.freepatentsonline.com/5734725.pdf (http://www.freepatentsonline.com/5734725.pdf)

After about reading about four pages and scrolling ten billion times between the text and diagrams (should've printed it out!!) I got distracted by the woodgrain pattern on my desk, I realised that I wasn't taking it in, and probably didn't care.

I will find it hard to make enough time to read, digest and act on this info.  So I'm posting this in case somebody else who doesn't have cat food for brains can understand and implement it for the common good.  Maybe not for this amp, but maybe for something.

The SS amp in my post above actually doesn't sound bad when you push it a little. I was getting "Jon Lord" with a keyboard with it clipping a little. Past a certain point it got nasty but I wouldn't 'avoid SS clipping at all costs' either.

  In the days of my youth I was shown what it's like to have an amp !
 Then I reached that age where I too got to feel a volume ramp.
 No matter how I tried all my notes just came out sounding damp.
 Good Amps Bad Amps..you know I've had my share, with all the HV's they kept inside I was just too shy to dare...
 Still 16 I got an amp with a sound as sweet as could be...
 It only took a couple days...my speakers blow on me.
 I swore I'd find the driver..would last me 'till the end.
 Then I found some other places for money I could spend...ohwaoughh !
 Chorus.

Pete, you need to get out more...

:icon_mrgreen: :icon_wink:

Brilliant.

Pete, you're one of my favorite people. If you ever record that, I want a copy.

Jacob

Go Pete.
Hi
RE: What would you suggest instead of a regulator for dropping 19.5v down to 14 or 16v?

A simpler (equally power-wasting approach) is to use a couple of 1N4004s.  They take minimal space, provide polarity protection, handle an amp (or two) and drop 0.7V each.

Note, however, that very very few devices blow at 20V if they are rated at 18V (ie they take something like the 0.001 percentile voltage for failure and add a couple of volts).  An EEs might know about "padding" and "stacking" the ratings? e.g. LM386s are run way overvoltage

I notice that printer power supplies are often 32V and a couple of amps (around 50W).  Ideal for supplying a discrete amp.  It might run a pair of 12AU7s if you wanted a valve amp (a la Firefly).
cheers 

Quote from: petemoore on October 13, 2010, 07:42:52 AM
 In the days of my youth I was shown what it's like to have an amp !
 Then I reached that age where I too got to feel a volume ramp.
 No matter how I tried all my notes just came out sounding damp.
 Good Amps Bad Amps..you know I've had my share, with all the HV's they kept inside I was just too shy to dare...
 Still 16 I got an amp with a sound as sweet as could be...
 It only took a couple days...my speakers blow on me.
 I swore I'd find the driver..would last me 'till the end.
 Then I found some other places for money I could spend...ohwaoughh !
 Chorus.

(http://i385.photobucket.com/albums/oo294/GIFMaster1000/VirtualLight.gif)

Just a quick update: I decided to go in 2 directions with this.

One will be a super simple, tiny amp. It has a clean high impedance input buffer, volume knob, power regulation, and power amp. No EQ, no clipping, just clean amplification. It fits in a 1590A. 20 watts, and the nice chipamp features like automatic protection if the speaker terminals short, etc. So, a clean 20 watt amp that fits in a 1590a. Of course, you could build it in something bigger and add your favorite preamp. But even without an added preamp, you can plug your guitar straight into this guy.

Prototype PCBs have been ordered for this.

The second will be the one with 3-band EQ and a clipping/comppresion section. Still ironing out the details on that design. I wasn't too pleased with any of the common 3-band tone stacks, due to the inability to boost mids. I'm working on a gyrator-based mid section, with Baxandall bass and treble.

yeah that sounds cool,  20 watts is plenty for my needs, i like the idea of the eq section too. nice one taylor.

look forward to this one..rob.

20W in a 1590A? Count me in!  :)

Will it be a snug fit with input/output jacks?
Any need to make a hole for the heatsink?

Well, to me anything is a snug fit in a 1590a  :) I'm 6'1" with Sideshow-Bob-sized feet. The PCB is 1.1" x 1.7".

I don't think a heat sink will be necessary - the regulator and chipamp will need to be screwed to the enclosure, which according to my tests so far provides adequate heat-sinking.

I wanna build an 20watt amp too (power by 12-14valt). I have a preamp but I am not sure which power amp to build. It is my first amp but I built couple of stomp boxes before. So which project do you recommend (A cheap kit is fine too)?

Uh, well obviously I think you should build my amp rather than somebody else's.  :)

If you're looking for an unbiased opinion you'd get better responses by starting a new thread.

i think he means preamp with eq or just power amp...i think? anyway...I want the power amp badly! Whats the power supply like? Do I have to build it seperate or can I use a walwart type deal?

Ah, well comparing my 2 amps, one is just clean power with a volume knob. If you want any tone-shaping, distortion or sound enhancement of any kind, you'll need to add your own preamp to it, or build the full amp, which acts more like a guitar amp, where you can shape the tone and add overdrive.

Power supply: it will operate from a laptop power supply, in the range of 12-20volts. I will have details accompanying the build instructions on what power supply to use. But you don't have to build the power supply and there are no high voltages to deal with.

Hi Taylor, I logged on tonight to especially re read this thread, to find the thread has been updated is inspiring. I just received 5 x TDA2050 in the post today so will need to do a little messing around but in general your project will be going along similar lines to what i'm doing, although i want to build my amp into a cab/ combo style. I am also hoping to add onboard digital fx based around my own FV-1 module. I also have went for gyrator based tone section but on treble mid bass and presence. I might also addheadphone and speaker simulator outs. Mind i do get carried away with what i want.

Anyway  I just wanted to say i'm following this thread with great interest and I am looking forward to the next update.

this sounds sweet! Will this power amp be able to handle a bass as well ( assuming the proper preamp is used)?

Yep, I'm a bass player more than a guitarist, and I really like it, even without any EQ. Nice low end. It is 20 watts, of course, which isn't enough for a bassist playing live in most cases, but I do think 20 watts is louder than most people think. It's only half as loud as 200 watts. There is a weird watt obsession in the musical world, of which I used to be quite guilty. As a casual musician, I used to use a 1600 watt power amp because I thought I needed that much power.  ;D

LOL!!! I am actualy building a 5 watt Trainwreck style amp so I can actualy use the volume knob on 7 at a gig! Yeah I think 20 is good. I want to put a line out for live use anyway. I wil probably use a tube pre but tuned for guitar or tuned for bass accordingly.. I just want some good power amp choices and GOOD solid state power amps are hard to find. So how do I get a board, b.o.m. and parts?

I have to get the prototype boards (probably about a week and a half) then get the full run made (about 2 weeks more). So boards and documentation should be available in about a month.

sweet! I will be keeping an eye on this thread. Cant wait :icon_biggrin:

I'm really excited about this! I've been catching up on this and I was a little disappointed when you were talking about adding an integrated preamp. I'm really glad that you're making it possible to take that out! Someone else may have thought of it already, but what might be neat is to put it in a larger rack mounted enclosure with SEVERAL pre amps and a rotary switch much like a Line6 POD works to select different amp models. The possibilities are quite literally endless with a nice clean power amp! Can't wait! Count me in after I build my valvecaster and Ruby!

Since I work at Best Buy, I really like the idea of using a laptop power supply since I can get new ones for fairly cheap. Probably not as cheap as eBay though.

Quote from: bassmannate on November 08, 2010, 08:15:13 PM
Since I work at Best Buy, I really like the idea of using a laptop power supply since I can get new ones for fairly cheap. Probably not as cheap as eBay though.

I get all my laptop power supplies for $1.99-$4.99 at my local thrift stores (Goodwill and Savers).

Never found a bad one, and there's always a wide selection - even up to 150 watts!

Quote from: Taylor on November 07, 2010, 04:03:45 PMI'm working on a gyrator-based mid section, with Baxandall bass and treble.

An Ampeg man, eh? ;) Nice choice.

Any updates on this?

Just waiting on the proto boards. Should have them Wednesday. If all goes well with them, the final boards would be here about 2 weeks later.

What are we lookin' at cost-wise for the power-amp with PCB, ICs, etc.?

Was thinking it could be cool to have an option for a tonestack on the clean channel without built-in compression and overdrive.

I'd probably re-house my Dr. Boogie with this for a hot channel. Maybe a switchable 4x12 cab sim on the end?  :icon_evil:

Could be cool to build a Mesa/Boogie recto clean channel preamp to use for l33t Mesa clean tones.  :icon_lol:

Don't know an exact cost but it'll be fairly cheap. The only special parts are the power amp (TDA7240a) the regulator (LM338T) and the laptop power supply, all of which I will sell on my website, or else Aron will sell them in his store, for reasonable prices. If you want to source that stuff elsewhere, I encourage that, but I thought it would be nice to save on shipping if you could get those parts at the same time as you order the PCB.

Since there's no transformer it's about as cheap to build as any small pedal.

I wanted to point out if it's not clear that it's just the straight power amp PCB that's on the way. There's still some work to do on the full amp with EQ and everything. But what's nice about the power amp is that it's so small you can pair it with whatever you want to use as a preamp and fit it in a small space.

Quote from: Ben N on November 09, 2010, 05:12:33 AM

Quote from: Taylor on November 07, 2010, 04:03:45 PMI'm working on a gyrator-based mid section, with Baxandall bass and treble.

An Ampeg man, eh? ;) Nice choice.

Actually, I hadn't really looked at any Ampeg amps for inspiration - I mostly just played with the various tone stack calculators and concluded that not having a mid boost is really limiting. What Ampeg amps use this kind of setup? I'd definitely be interested to see how some other designs have implemented this combination.

Quote from: Taylor on November 16, 2010, 12:05:46 AM

Quote from: Ben N on November 09, 2010, 05:12:33 AM

Quote from: Taylor on November 07, 2010, 04:03:45 PMI'm working on a gyrator-based mid section, with Baxandall bass and treble.

An Ampeg man, eh? ;) Nice choice.

Actually, I hadn't really looked at any Ampeg amps for inspiration - I mostly just played with the various tone stack calculators and concluded that not having a mid boost is really limiting. What Ampeg amps use this kind of setup? I'd definitely be interested to see how some other designs have implemented this combination.

Yeah, I'd love to see some too! Looking for a good bass preamp to put in front of this thing! As quickly as this seems to developed, I'm really curious to see a schematic and BOM.

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44014&g2_serialNumber=2)
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44017&g2_serialNumber=2)

Well, fellas. Here we have a complete 20 watt clean instrument amplifier (clean preamp and power amp) in a 1590A box.

The good news is that it works and sounds massive (even with a bass). The bad news is that I need to change a couple of things in the PCB design which means another rond of prototype PCBs.

To clarify what this PCB is/does: it has a clean preamp with high input impedance, and a decent amount of clean gain so you can plug your passive guitar straight in without losing high end. This then goes to a 20 watt power amplifier. There is an onboard power regulator to take a variety of power supplies and get them to where the power amp is working as it should.

There is no EQ or clipping on this PCB. It's intended to be the clean power, which you can pair with whatever sound shapers you want.

How did the heat dissipation turn out,

And where do you get your PCB's made? I was looking to do a prototype run myself for something I've been cooking up. It's a 6.5x2".

Gets slightly warm to the touch, not hot at all. But I haven't been able to really stress test it as its way too loud for my house and I'm not a gigging musician. I'll see if I can get somebody to really punish it with loud volume for an extended time to see how it goes.

For prototype PCBs, pcbfabexpress.com.

Go Taylor!  I'm drooling now...

I take it that the IC at the top-left is an LM338?  And the thin brownish thing is an insulator to keep the tab from shorting against the enclosure?

-Walt

Neat! I've been looking into little power amps, this one looks great!

Now I just need a more powerful one to replace my clunky Crate Powerblock for gigging situations. :D

Quote from: waltk on November 19, 2010, 08:10:41 PM
Go Taylor!  I'm drooling now...

I take it that the IC at the top-left is an LM338?  And the thin brownish thing is an insulator to keep the tab from shorting against the enclosure?

-Walt

As you know, I stole most of what's going on here from you!  :) Yes, it's an LM338 and the brownish thing is a very thin insulator meant just for this purpose. The screw that holds the chip to the enclosure has heat shrink around it to avoid shorting to the enclosure. When I get the real boards made, I'll offer some plastic screws to make this simpler. I really wish there was a regulator that could handle this amount of current but didn't need to be isolated. Haven't found one yet.

Taylor that is some sweetness goin on there and you are kind of my hero now. Well at least you are up there the Doug H and Rick H. G

Quote from: Taylor on November 19, 2010, 08:32:31 PM

Quote from: waltk on November 19, 2010, 08:10:41 PM
Go Taylor!  I'm drooling now...

I take it that the IC at the top-left is an LM338?  And the thin brownish thing is an insulator to keep the tab from shorting against the enclosure?

-Walt

As you know, I stole most of what's going on here from you!  :) Yes, it's an LM338 and the brownish thing is a very thin insulator meant just for this purpose. The screw that holds the chip to the enclosure has heat shrink around it to avoid shorting to the enclosure. When I get the real boards made, I'll offer some plastic screws to make this simpler. I really wish there was a regulator that could handle this amount of current but didn't need to be isolated. Haven't found one yet.

Wait...I'm new to this so it may be a stupid question, but the heat sink tab is connected to something other than the ground pin?   ???

Quote from: zambo on November 19, 2010, 08:32:54 PM
Taylor that is some sweetness goin on there and you are kind of my hero now. Well at least you are up there the Doug H and Rick H. G

I don't know about that - those guys are kings to a peasant like me. But thanks.  :)

Quote from: bassmannate on November 19, 2010, 08:37:50 PM
Wait...I'm new to this so it may be a stupid question, but the heat sink tab is connected to something other than the ground pin?   ???

Correct. The heat sink tab of the power amp is ground, but the power regulator (the other tabbed IC in a TO-220 package) is "floating" (no ground) and the tab is connected to the voltage output. So if you connect this to the case, it would short the positive voltage to ground.

Quote from: Taylor on November 19, 2010, 08:41:58 PM
Correct. The heat sink tab of the power amp is ground, but the power regulator (the other tabbed IC in a TO-220 package) is "floating" (no ground) and the tab is connected to the voltage output. So if you connect this to the case, it would short the positive voltage to ground.

I guess that makes sense...Most manufacturers I guess would put a dedicated heat sink on something like this so you wouldn't worry about the tab grounding out. I still think it would make more sense to have the tab on the regulator be ground to give you the option to sink it to the case. Oh well. engineers with a heck of a lot more education than me design these things so who am I to question it!   ;D

Quote from: Taylor on November 19, 2010, 08:32:31 PM

Quote from: waltk on November 19, 2010, 08:10:41 PM
Go Taylor!  I'm drooling now...

I take it that the IC at the top-left is an LM338?  And the thin brownish thing is an insulator to keep the tab from shorting against the enclosure?

-Walt

The screw that holds the chip to the enclosure has heat shrink around it to avoid shorting to the enclosure. When I get the real boards made, I'll offer some plastic screws to make this simpler.

I assume you haven't seen the plastic washers (shown below as "bush") made specifically for this purpose - they have a lip that goes inside the TO-220 metal tab and prevents the screw from touching the transistor.
(http://www.techedge.com.au/vehicle/wbo2/1v5/to220i.jpg)

You are correct in your assumption! Thank you for the tip, and I've now located a whole assembly with mica spacer, bushing, etc.

BTW, googling "bush screw" does not turn up electronic info.  :icon_idea:

Quote from: Taylor on November 19, 2010, 10:13:25 PM
You are correct in your assumption! Thank you for the tip, and I've now located a whole assembly with mica spacer, bushing, etc.

BTW, googling "bush screw" does not turn up electronic info.  :icon_idea:

I can only guess that whatever you get when you google "bush screw" is not "family friendly"  :icon_lol:

Quote from: bassmannate on November 19, 2010, 10:15:09 PM

Quote from: Taylor on November 19, 2010, 10:13:25 PM
You are correct in your assumption! Thank you for the tip, and I've now located a whole assembly with mica spacer, bushing, etc.

BTW, googling "bush screw" does not turn up electronic info.  :icon_idea:

I can only guess that whatever you get when you google "bush screw" is not "family friendly"  :icon_lol:

Ahahaha, I can see how that might cause erroneous results....

The correct form "bushing" might help a little  :icon_rolleyes:

Quote from: azrael on November 19, 2010, 08:15:04 PM
Neat! I've been looking into little power amps, this one looks great!

Now I just need a more powerful one to replace my clunky Crate Powerblock for gigging situations. :D

I have looked into the issue of bigger power (in the 150 w range), speaking to a guy I know who really knows his stuff (designed class D amps for use as camera stabilization mounts or something, in addition to knowing guitar tech well). I would say that it's unlikely to be possible to make anything in that power range feasible as a DIY project, and it wouldn't be appreciably smaller than the power block even if we could do it.

The problem is the power supply. As noted to me in the threads that preceded this one, power out is equal to power in, minus losses. Even though class D is very efficient, there will still be something like 25% lost. So to get 150 watts out, we need something like 200 watts in. A power supply like this ain't cheap. Looks like $70 for an internal supply, which would not be safe for noobs to mess with. An external one like that is around $100. You can buy a Power Block for $100 if you look. And it would be unlikely to be any smaller than the PB. So as much as I wanted this to happen, I don't think it will.

With that said, 2 of these PCBs would be 40 watts into two 4 ohm speakers. That's loud. 40 watts is only half as loud as 400 watts. So for all the cost and complexity of 150w, you wouldn't really gain that much. To put that another way, 2 of these PCBs in one box is only barely quieter than a Powerblock. 

Quote from: Taylor on November 19, 2010, 06:24:37 PM
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44014&g2_serialNumber=2)
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44017&g2_serialNumber=2)

Well, fellas. Here we have a complete 20 watt clean instrument amplifier (clean preamp and power amp) in a 1590A box.

Thats incredibly nice.
Much more compact than I had imagined.
Well done Taylor!

any mp3 on this? sound testing? this is nice project! :icon_biggrin: :icon_evil:  :icon_razz: :icon_twisted: ::) ;D

Since it's a completely clean amp, it would be difficult to make a sound clip that would really show anything meaningful. You'd mostly be hearing my instrument (an 8-string bass), my speaker (a vintage Electro Voice 15"), my cheap microphone, etc. It wouldn't really tell you anything. It sounds like what you put into it, but louder.

so for the volume challenged among us, is it possible to bridge two of these and run 40 watts into one speaker? ( i am ok with 20 but i know a lot of bass players and they always want more headroom....)

This amp is itself already a bridged amp, so I kind of don't think it's possible to bridge 2 bridged amps into one speaker, but I will investigate this.

Can't double bridge them. The only reason you can bridge amplifiers is because they have a ground connection that is fixed and an amplifier that outputs a signal around ground. When bridging, you replace this ground with another of the same amplifier. Already bridged amps don't have a fixed ground, they need connections to both ends of the speaker to work.

Unless you use some sort of output transformer to arrange it all.

Quote from: zambo on November 20, 2010, 02:57:50 PM
so for the volume challenged among us, is it possible to bridge two of these and run 40 watts into one speaker? ( i am ok with 20 but i know a lot of bass players and they always want more headroom....)

I'm a bass player and I never really understood the power fascination. I have a little 120w combo 1x10 and I rarely ever get it up past half way. I don't normally need to, but if I ever have a need for more volume, the venue is usually big enough to have a PA that I can mic the amp with. Just don't get it. 20-40w would be plenty for me!

yep 20 watts of a nice clean amp would suffice...i'll dirt it up later on..nice work taylor.

i'm just waiting for the eq version... :icon_wink:

Nice work Taylor, looking forward to the PCBs.

Quote from: Taylor on November 19, 2010, 11:09:29 PM
I have looked into the issue of bigger power (in the 150 w range), speaking to a guy I know who really knows his stuff (designed class D amps for use as camera stabilization mounts or something, in addition to knowing guitar tech well). I would say that it's unlikely to be possible to make anything in that power range feasible as a DIY project, and it wouldn't be appreciably smaller than the power block even if we could do it.

The problem is the power supply. As noted to me in the threads that preceded this one, power out is equal to power in, minus losses. Even though class D is very efficient, there will still be something like 25% lost. So to get 150 watts out, we need something like 200 watts in. A power supply like this ain't cheap. Looks like $70 for an internal supply, which would not be safe for noobs to mess with. An external one like that is around $100. You can buy a Power Block for $100 if you look. And it would be unlikely to be any smaller than the PB. So as much as I wanted this to happen, I don't think it will.

With that said, 2 of these PCBs would be 40 watts into two 4 ohm speakers. That's loud. 40 watts is only half as loud as 400 watts. So for all the cost and complexity of 150w, you wouldn't really gain that much. To put that another way, 2 of these PCBs in one box is only barely quieter than a Powerblock. 

Oh, I know, I'm not looking to get a 150W amp. One that would work to get over drums would be cool, though. :D

Quote from: Taylor on November 20, 2010, 03:01:56 PM
This amp is itself already a bridged amp, so I kind of don't think it's possible to bridge 2 bridged amps into one speaker, but I will investigate this.

awesome!

Regardless of what happens, looking forward to grabbing one. :D

Quote from: Taylor on November 16, 2010, 12:05:46 AM

Quote from: Ben N on November 09, 2010, 05:12:33 AM

Quote from: Taylor on November 07, 2010, 04:03:45 PMI'm working on a gyrator-based mid section, with Baxandall bass and treble.

An Ampeg man, eh? ;) Nice choice.

Actually, I hadn't really looked at any Ampeg amps for inspiration - I mostly just played with the various tone stack calculators and concluded that not having a mid boost is really limiting. What Ampeg amps use this kind of setup? I'd definitely be interested to see how some other designs have implemented this combination.

Sorry I didn't get back sooner. Here's are a few examples: http://www.unofficialampeg.com/schematics/v4preamp.gif (http://www.unofficialampeg.com/schematics/v4preamp.gif), http://www.unofficialampeg.com/schematics/v9preamp.gif (http://www.unofficialampeg.com/schematics/v9preamp.gif), http://www.unofficialampeg.com/schematics/svtpream.gif (http://www.unofficialampeg.com/schematics/svtpream.gif). My memory failed slightly, as these are all inductor based, but (with apologies to Clausewitz) what is a gyrator if not an inductor by other means, right?

Upgrade (http://www.silabs.com/products/audiovideo/class-d-audio-drivers/Pages/Si824x.aspx)
yer (http://pdfserv.maxim-ic.com/en/an/AN4526.pdf)
AMPs... (http://www.farnell.com/datasheets/613604.pdf)

 :icon_eek:

Quote from: puretube on November 28, 2010, 05:22:37 PM
Upgrade (http://www.silabs.com/products/audiovideo/class-d-audio-drivers/Pages/Si824x.aspx)
yer (http://pdfserv.maxim-ic.com/en/an/AN4526.pdf)
AMPs... (http://www.farnell.com/datasheets/613604.pdf)

 :icon_eek:

The problem with some of those chips is that they're not nearly simple enough for noobs like me. surface mount and 64 pins just doesn't sound like a fun soldering day to me.

surface mount isn't bad if you work carefully. but 64 pins ick
:P

Nice stuff Taylor

Taylor...how is everything coming along?

Second round of prototypes check out just fine, so I've ordered the actual run. Normally this takes about 2.5 weeks, not sure how much this will be effected by Christmas.

Quote from: Taylor on December 08, 2010, 02:07:04 PM
Second round of prototypes check out just fine, so I've ordered the actual run. Normally this takes about 2.5 weeks, not sure how much this will be effected by Christmas.

Nice. I'm really excited! Any idea on costs yet?

Here is the schem.

http://musicpcb.com/wp-content/gallery/pcbs/tiny-giant-schematic-copy.jpg

Parts list:

Quantity-part

Resistors
all 1/4 watt

1 - 100k
1 - 220k
2 - 1m
2 - 2.2R   [Marked "2R2" on the board - this is 2.2 OHMS]
1 - 1k
1 - 120R  [120 OHMS]

Capacitors
[cap types are just suggestions - if you prefer something else and you know what you're doing, feel free to substitute]

1 - 10uf electrolytic
3 - 100n film
2 - 1uf film
2 - 220n film
2 - 22uf electrolytic
1 - 470uf electrolytic

ICs

1 - TDA7240A
1 - LM338T
1 - TL072

Power supply:
Detailed info will be available in the PDF. You should be able to get a good supply for around $10 on ebay.

Q. Why did you use a dual opamp when only one opamp is used?

A. 2 reasons: dual opamps are much more common, so people are more likely to have them on their bench already, and because the TL072 is usually cheaper than the TL071 (by a couple of cents).

Would heatsinks be a good optional component? i.e. for larger enclosures
Any suggestions?

I'm using the enclosure as a heatsink. The reason is that unless you're using a much larger enclosure, you'd need to somehow cut a square in your box to have the heatsink sticking out. If you were going to build this in a wooden head case like a tube amp, then heatsinks would make sense. Probably best to have the sinks exposed to open air, rather then sealed up inside a box, so the ambient air can dissipate heat. Mounting to the enclosure is just a convenient solution to these issues.

This info will be in the PDF, but it's important to note that the regulator heat sink tab MUST be isolated electrically from the heat sink.

will you make a pcb for it? ;D

Quote from: tasos on December 09, 2010, 03:29:30 PM
will you make a pcb for it? ;D

http://musicpcb.com/future-projects/
I do think so :D

so i have to buy the pcb?isn't there a pcb ready to print or just the pcb in a picture? ;D

Why are you using a regulator?  You might be able to use a power resistor and a cap (RC size the cap for feel)to drop the voltage and this might help the sound if it is used for guitar by adding a sag to the power supply.  If you do that add a resistor and cap at the PS input to the 72  decouple the 72 from the power amp rail a little.  Think of it like a Y to split the power two ways

I would change the input to a voltage divider 10K, 10K with a cap at the node to ground and a resistor from that node to the 72 + input.  This will allow you to easy change the input resistance you could even make the input resistor a 100K with a 1meg pot.  You might want to add a series resistor at the input(all part of making things work in the real world)

You could also use a lin pot for a volume control select the value to taper it  to a log/audio curve with the input resistance of the amp chip(70K from the data sheet).

Although I appreciate that, the boards have already been ordered, so too late for any changes. The amp works exactly as I want it to, so I don't really see any reason to change it. It's not only for guitar, so I don't want sag. Again though, thank you for your suggestions.

Does this design really need a LM338T, or will a LM317T suffice?

317 does up to 1.5A... TDA7240a says max repetitive current is 3.5A. I will try to measure actual current when in use in the real world, but I'm guessing the 317 will not be enough.

powersupplies to poweramps are usually unregulated as it means more components that needs cooling and sometimes/usually limit the possible output of the amplifier..wastefull use of energy..but I guess for such small and simple design it might be the better thing as you did.
personally, I'd just hook up the power chip to 19volts and regulated the TL072 voltage with a resistor a Zener and a cap...good job non the less.. ;)
J

Have the PCB's been finalized and ordered,  using the second part TL072 op amp could have powered another TDA7240 for stereo, that would be a nice option,  if only mono is wanted the extra components may just be left out.

wow, this is great, thank you so much for designing this!!  :)

Now, a couple of questions, please forgive me if they have been answered in one of the preceding 11 pages that i didn't read...

Do you recommend any certain type of tone stack?  And can I insert it right before the volume control?

How "flat" is the frequency response?

Would this play nice if i used a tube preamp (valvy) instead of the standard SS one in the schematic?

What are the approximate power ratings at 16, 8, and 4 ohms?  Do you think i'm ok driving a 2x12 4ohm cab with this?

Thanks again, great project!  

Quote from: Johan on December 14, 2010, 01:10:21 PM
powersupplies to poweramps are usually unregulated as it means more components that needs cooling and sometimes/usually limit the possible output of the amplifier..wastefull use of energy..but I guess for such small and simple design it might be the better thing as you did.
personally, I'd just hook up the power chip to 19volts and regulated the TL072 voltage with a resistor a Zener and a cap...good job non the less.. ;)
J

True, but most power amps are run on traditional linear power supplies. This is meant to run from a laptop SMPS, which will already be regulated, so I don't think it will limit the output. If we powered the chip off of 19.5v then we'd just have to get rid of al of that excess heat anyway, and risk damaging chips.

Quote from: Ice-9 on December 14, 2010, 01:26:05 PM
Have the PCB's been finalized and ordered,  using the second part TL072 op amp could have powered another TDA7240 for stereo, that would be a nice option,  if only mono is wanted the extra components may just be left out.

The idea here is that if you want stereo (as I do) you can use a second board. "Wasting" a single opamp makes more sense to me than wasting all the extra board space necessary to add an extra power amp to each chip, when most people won't use that.

Quote from: runmikeyrun on December 14, 2010, 02:11:56 PM
wow, this is great, thank you so much for designing this!!  :)

Now, a couple of questions, please forgive me if they have been answered in one of the preceding 11 pages that i didn't read...

Do you recommend any certain type of tone stack?  And can I insert it right before the volume control?

Note that I will be doing a different PCB with integrated EQ and clipping preamp, so you may want to wait for that. If you want to add your own EQ, I would recommend that you use an active EQ and do it before the amp's preamp. Using a passive tone stack after the opamp but before the amp could cause weird loading issues I would think.

QuoteHow "flat" is the frequency response?Would this play nice if i used a tube preamp (valvy) instead of the standard SS one in the schematic?

What are the approximate power ratings at 16, 8, and 4 ohms?  Do you think i'm ok driving a 2x12 4ohm cab with this?

The datasheet doesn't show the freq response, but it's down 3db at 30 hz and 25khz. I think we can say that it's certainly flat enough for guitar/bass/key use. It's meant for reproducing full range audio, so it will be flatter than just about any stompbox.

If I were you, I'd use the opamp stage still, and run your tube preamp into that. 20w at 4 ohm, 12 at 8 ohm. A 2x12 should be good.

awesome, thanks for the input!  i'll wait for the board with the eq.  As for the valvy, we'll see how it sounds first.

I'm dying over here, Taylor.....need PCBS!!!!! haha

Just got an idea...If I wanted to, could I use the other half of the dual op-amp to feed a second power amp chip? I realize that I'm not saving much in the way of cost ($0.80?) but I guess it has the potential to save some space if I wanted dual outputs.

Hi Taylor,

I was wondering if you considered this module at all:

http://www.electronics123.com/s.nl/it.A/id.325/.f

Different pre-amps would work well with this depending on what you need.  A high impedance buffer followed by volume control right into this module would work well for a pedal amplifier.  The module also works from a single sided power supply, so your use of a wall wart would still suffice.  You can get ~ 18 W with a 13.2VDC power supply and a 4 ohm load.  It would just need to be added to a pretty box then.

You can spend a little less and get a 15W power amp kit like this: http://store.qkits.com/moreinfo.cfm/FK607 $10 is tough to beat.. and it will work with a run of the mill 12V wall wart.

I can vouch for that amp kit. I built one with a LM386 as the preamp and it sounded great. Nice and loud with a 6" weber signature speaker in a custom combo cabinet. Taylor's design is going to be better in terms of having a clean guitar-friendly preamp already integrated on board. If I wanted a clean guitar amp I would probably choose taylor's design.

That was what I was alluding to.  One of these kits may be an easier/cheaper method.  Pre-amp boards could be built up from a buffer/volume board to a full blown pre-amp and would then just need to be tacked onto the power module.

Hi Taylor,

I was wondering if the schematic you show in post #220 above is your final schematic?  Are you open to any comments about the parts values and bias scheme?

Uh, well, I'm open, but at the same time, the PCBs already have been designed and are being fabricated. So I can't really do anything to change them now.

Hey, Taylor,

What kind of speaker cab are you using for bass with this thing?

I have a TL606 cab loaded with an EVM 15L, I think. This is a very nice cab for it's time, but these days there are better speakers which are lighter, go lower, have better sensitivity, etc. and much better cab designs.

Some day when I get a lot of free time I'd like to build one of Bill Fitzmaurice's (http://billfitzmaurice.com) designs, like the Jack. His stuff would be great to pair up with my little amp design, because they are horn designs so the sensitivity is through the roof compared to direct radiator cabs. You could get a lot of volume and great frequency response with just 20 watts through one of his cabs.

Still being manufactured. There was a bit of a delay because of a misunderstanding with the factory. Should be available pretty soon though. I'll post here when they're available.

PCBs are now available:

http://musicpcb.com/pcbs/tiny-giant-amp/

Hm, but where to buy TDA7240As....?

Looks great Taylor! I think I'll be getting some of these.

How would one adapt this for use with bass?

I will have a bunch of info on parts sourcing on the site in the next day or two. There are plenty of sources for the chips, and I'll also have parts kits which include the TDA and everything else on the board for pretty cheap.

I use mine with bass without any modifications. It's a full-range amp - the chip is designed to reproduce full spectrum audio for car audio systems, so it doesn't have a guitar-specific voicing.

The "audiophile" thing to do for more bass would be to increase the power supply reservoir cap. It's already bigger than the datasheet suggests, but you could make it really huge like 4700uf or even bigger probably. Not sure if this makes a difference in real life.

A good thing to do would be to pair it up with a nice EQ - I like a couple of bands of semi-parametric EQ. But the amp itself can handle and dish out lows quite well.

Quote from: azrael on January 12, 2011, 10:15:23 PM
Hm, but where to buy TDA7240As....?

2 bucks a piece on Mouser.  They've got 400 of them right now, so get in while the gettins good [/sarcasm]. May as well get the 2R2 resistors while you're there too. 

This is a cool project.  I'm going to have to find a use for some of these. 

Taylor, would it be possible to parallel the boards/chips for more power into higher loads?  Google and the data sheet was of no help in telling if the TDA7240A plays well if paralleled. 

Yes, Mouser has them. Last time I looked all they had were the backwards-bending ones (with H at the end of the part number) but now they have the ones that stand upright, which is what you want. You can also find them on ebay for pretty cheap, and for a dollar each here, but unless you're getting something else from there the shipping might not make it worthwhile:

http://www.packetradio.com/catalog/index.php?main_page=product_info&cPath=24&products_id=1003

You can't bridge the amps because they're already bridged. I think it's possible in theory to parallel them, but when I read up on it, it seemed that it was very important to match the output resistors or else one of the chips will pull current from the output of the other one and they could get damaged.

I want to parallel them too, so I will be researching and experimenting with that to see if it works in reality.

This project is ideal for me. I play keyboards, bass, and guitar and have been pondering how to have one amp that can serve all my purposes. I think it might be fun to build just one amp but then have options of different cabs for different situations and instruments. Great 2nd hand speaker cabinets with lots of character are the kind of things that are always popping up around Portland.

- Strategy

Quotewould it be possible to parallel the boards/chips for more power into higher loads?  Google and the data sheet was of no help in telling if the TDA7240A plays well if paralleled.

The chip is already in a bridge configuration, so you can't parallel two chips into one speaker.  You could easily just build two boards, hook up a separate speaker to each, and then put a splitter in front of them.  In fact, you might not even need a splitter because the input is fairly high impedance.

Edit: Ooops, Taylor already answered this.

Right, as Walt says, and I forgot to mention, the easiest way to get more power is to plug 2 of these into 2 speakers. Double speaker area gives you 3db boost on its own, so adding a second speaker and power amp would give you quite a bit more volume.

Taylor that board is lookin sweet! Do you have the full kits available yet?

Thanks zambo, I will have the kits all ready to go tomorrow.

Since these are full range I could use them to power a small pair of speakers, right?

Anybody have any thoughts about using 2 of these to make a true stereo chorus amp (a la Roland "JC") :icon_question:

Discuss... :D

Quote from: therecordingart on January 15, 2011, 10:38:55 AM
Since these are full range I could use them to power a small pair of speakers, right?

You mean like stereo speakers? Yes, definitely - that's what the chip was designed for. But I must admit I have no knowledge of stereo equipment in terms of in and out impedances, so I can't say with certainty how the opamp buffer would work for non-instrument signals.

Quote from: oldschoolanalog on January 15, 2011, 02:45:50 PM
Anybody have any thoughts about using 2 of these to make a true stereo chorus amp (a la Roland "JC") :icon_question:

Discuss... :D

Yeah, that kind of thing was one of the reasons I decided to do this simple power amp design - that way people can easily incorporate it into projects like that, or mini-Leslie clones, etc. I think it would be really cool to see these built into a cab with outward-angled speakers to do a stereo spread thing.

I think you are a better person for designing this and should therefore pm me with a price for a full kit in us dollars or chickens or bushells of wheat.  :icon_mrgreen: It may be a little bit before i can buy one but i am for sure interested. I just fired up my tube pre and want to make the mini hybrid wreck! 20 watts of love!

I'd take some home grown chickens or vegetables (seriously) if we were in the same state.  8)

Kits will be up on the site tonight or tomorrow...

I definitely want to see some cool hybrid amps made with this PCB. At first I was thinking of doing a Valvecaster with it, since the V-caster's already for 12v. I might still do that. But I also want to try doing something with the SMPS from FrequencyCentral's submini amps and do a real high voltage preamp.

The build PDF is up now:

http://musicpcb.com/pcbs/tiny-giant-amp/

Please check it out and let me know what you think. Questions left unanswered, any spelling or grammar issues you see, things that need some clarification, etc.

Hi taylor,

Any news on the price for the kit?
Depanding on price, I would be in for a couple boards.

Andreas

Kits are now available:
http://musicpcb.com/pcbs/tiny-giant-amp/

FYI, the price on the web site is the same for the PCB or the kit ($9). I'm assuming this was not your intention :)
-Matt

Quote from: armstrom on January 17, 2011, 03:49:22 PM
FYI, the price on the web site is the same for the PCB or the kit ($9). I'm assuming this was not your intention :)
-Matt

Looks like it's $9 for the PCB + $9 for the kit.

Right, the parts kit is a parts kit - it does not contain the PCB. It contains only the stuff listed under "the kit contains" and shown in the photo.

I don't know, is that confusing? Do you guys think I should do it another way?

Just use the shopping cart folks... :icon_rolleyes:

Quote from: Taylor on January 17, 2011, 03:59:22 PM
Right, the parts kit is a parts kit - it does not contain the PCB. It contains only the stuff listed under "the kit contains" and shown in the photo.

I don't know, is that confusing? Do you guys think I should do it another way?

Maybe put "PCB + Kit" for 18$

Then again, sneaky bastards trying to "take advantage" of your "mistake" will be surprised when there's no PCB in their kit  ;D

Quote from: Taylor on January 17, 2011, 03:59:22 PM
Right, the parts kit is a parts kit - it does not contain the PCB. It contains only the stuff listed under "the kit contains" and shown in the photo.

I don't know, is that confusing? Do you guys think I should do it another way?

..now that you point it out, it's clear...but I did the same mistake as Josh when looking the first time. that makes us two, and I'm sure many more could easily make the same mistake.....perhaps calling the partskit something else, like "population-kit" or something, just to be extra clear...it looks good thou.. ;D
J

OK, I just went ahead and restructured it. Originally, the parts kit did not include the PCB and was $9. Now it includes the PCB and is $18.

So if you just want the board, click "purchase PCB only"

If you want the board and parts kit, click "purchase PCB and parts kit"

Hopefully that's more intuitive. Thanks for the feedback, guys.

Hi! i would like to build this one and buy a PCB but howto mod this as bass amp?

A2

You don't really need to mod it to use it as a bass amp. I use it for bass and it works well.

You'd probably want to add an EQ in front, but it will work as a bass power amp with no mods.

thanks so much!

Quote from: Taylor on January 29, 2011, 11:33:26 PM
You don't really need to mod it to use it as a bass amp. I use it for bass and it works well.

You'd probably want to add an EQ in front, but it will work as a bass power amp with no mods.

Im interested in buying this Taylor but just wondering about the EQ version you are going to do? When will that be ready? I can't really find any info on it in this thread? I kinda want to make a project out of this for myself and design the preamp and EQ but Im interested in what you have to offer.

I have not had time to work on that, so It's probably fairly far off at this point.

Quote from: Taylor on May 10, 2011, 02:05:52 PM
I have not had time to work on that, so It's probably fairly far off at this point.

Ok no problem. Big project for me during the summer so :)

Thanks man

I was looking to make a portable amp that ran off of a 12 volt scooter battery, what would you think about bypassing the power supply segment and just using the straight 12 volts to power this amp?

I don't know anything about scooter batteries, but I would assume they can deliver enough current to do the job. I bet PRR knows the answer to that. Maybe he'll see this.

Waltk built a portable amp similar to this using one of those rechargeable drill batteries.

QuoteI was looking to make a portable amp that ran off of a 12 volt scooter battery, what would you think about bypassing the power supply segment and just using the straight 12 volts to power this amp?

A 12-volt SLA scooter battery would power it just fine.  If you do this, bypass the LM338T.  You can probably come up with a wiring scheme that allows powering from either the battery or a laptop adapter. 

I've used higher voltage batteries, and in that case, you still need to pass it through the VR because the TDA7240 is sensitive to voltages over spec. (I've done this, and the result is not good).

I just (finally!) got mine built, worked great right off. I set mine up to run off either the 19.5v laptop supply or 12 volt battery, using a 2.1mm power jack for the 19.5v input and a 2.5mm for the 12v (so that the 19.5 can't accidentally get plugged into the 12 v input). Both jacks are set up with tip=negative. The 19.5 is wired to the power pads on the PCB as designed. The LM338 has its output pin lifted from the board. The 12v jack positive goes to the pad where the 338's output pin would normally go. The 338's output is wired to the break contact on the 12v jack so that if nothing is inserted in the 12 volt jack, the output of the 338 goes thru the jack and back to the board. Works like a charm!

I realize the project is already done and i'm a bit late for saying that, but how impossible would it be to design a super precise and dynamic, easy to carry amp? (think AER, enricksen, polytone,...)
My perfect design would be : light and easy to carry (aer compact 60 is GREAT for that), combo, clean sound only, as flat as possible, para eq 3 bands (can be a normal eq if that's too much work), lots of dynamics, lots of precision, large frequency response, no effects (or a very small and subtle reverb (equinox?)). Volume should be enough to play with a reasonable drummer and 2-3 others bandmates in researshals/small clubs/gigs.
I am certain that some people here have references for getting cabinets, chassis, faceplates, speakers, ...
It would be nice to try to make a complete amp kit from the collaboration of people in this forum.

Just in case some of you like the idea.. i'm just starting the diy thing and i'm not able to design that at the moment, but i think the idea would be nice.

http://www.lunchboxamp.com/

It could be done DIY too, but the challenge is coming up with a lightweight combo of speaker and cabinet that doesn't sound like a practice amp. (I'm assuming you DON'T want the practice amp sound). Keep in mind that the lunchbox amps are small, but not as light as you would expect from looking at them.
-Matt

The Tiny Giant would do fine for that if you gave it a generous power supply, paired it with an efficient speaker, and maybe filled out the front end with a tonestack and clipping.

what is the current draw of this amplifier?

Quotewhat is the current draw of this amplifier?

When you first turn it on, it spikes up to a little over 1 amp (1.14a in a quick test I just did).  Then it settles down to 70ma with no signal through it.  When you're playing the current draw depends on how much current is being output to the speaker - but even at very high volume, it doesn't draw much more than 1 amp.

Awesome thanks! Im planning on using a 12 volt scooter battery to make this into a backpack amp

are there supposed to be any jumpers on this board? I put one under the IC holder, I built this amp, and it is totally not working correctly, the only time it will work right is one sweet spot on the knobs of my guitar, it does it on multiple instruments

No, there are no jumpers. Any part that needs to be filled is labeled, so don't put in any parts that it doesn't tell you to put in.

The things you might be thinking are for jumpers are called vias (http://en.wikipedia.org/wiki/Via_(electronics)). They connect the top copper layer and the bottom copper layer. Don't put anything in them or do anything with them, they're just part of the PCB design.

The build/debug thread for this project is here:

http://www.diystompboxes.com/smfforum/index.php?topic=89687.0

[Wrong topic. Please delete this post]