The "Forum Amp" design thread

[culturejam]

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.

[Taylor]

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.

[culturejam]

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.

[armstrom]

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

[Taylor]

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.

[Nasse]

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 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

[John Lyons]

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.

[armstrom]

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.

[armstrom]

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

[John Lyons]

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.

[Taylor]

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.

[DaveM]

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

[Taylor]

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.

[Derringer]

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

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.

[Derringer]

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.

[armstrom]

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.

[jkokura]

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

[Taylor]

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?

[jkokura]

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

[clamup1]

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