Enough with Pedals, what about amps

[Satan Of Saturn]

After making a few pedals, i was kinda interested in making a proper bass amp of say 60-100 watt (solid state)... Anyone having any reference or PCB layout for that? Interested in something similar to Hartke or say Bassman. Found a few schematics but they were just like a tangent on my head :-D

[Gus]

A 9VDC battery power effect is more safe than an amp.

[Ice-9]

To be honest an amp isn't really much more complicated than a stompbox, at least in a simple amp format forgetting amps with midi control and digital effects etc. The way to look at an amp schematic would be to break it down into its building blocks. Most amps will have sections similar, like Input and impedance changing - Tone section - Power amp and a PSU. If you have a schematic in mind then post the drawing if possible. Myself and others would be happy to point out which bits of the schematics do what they do.

Always keep in mind though that amps run from higher voltages and mostly from a mains supply so always keep safety in mind when working with amps. Electric shocks WILL KILL.

[R.G.]

It goes something like this. A metal box with a circuit board inside will do for a pedal. Things get complicated with the much larger, heavier, and hotter things in an amp. The mechanical, not the electronic stuff gets much harder. Unless you are a well versed woodworker and minor-skilled metal worker, this is going to be a huge task you may never accomplish.

The work comes in two flavors: head and cab amplifiers and combos. Head and cab is paradoxically easier, as the funny requirements for a head and for a cab separately don't have to be combined as they are in a combo, and the mechanical vibration and shaking the speakers give the electronics in a combo are not issues (at least so much) in an H&C.

You'll also have to master the appearance issues of covering or painting or SOMETHING to make the exterior cabinet look OK. And once you're OK with that, you'll have to make or buy a metal chassis to hold the electrical stuff, and yep, you'll have to know how to wire AC power safely.

And that's all before you have said one word about what goes inside the cabinet. A power amplifier PCB is not even close to a guitar amplifier. It only seems like it is because, hey, I have this here 100W amplifier on a card. Yeah, well, you now need a 100W DC power supply that meets its needs, AC power wiring that can kill you or someone else, even years later, and a metal chassis, and a box to put it in that also looks OK and is sturdy enough to sit in your bedroom, let alone haul to a gig. And a speaker cab.

The power amp PCB is seductive - but like most seductresses, it delivers less than your mind thinks it will.

Ask me how I know these things...   

I have mastered the sets of skills. I can do all of those. I still would probably not go build my own amp because the huge amount of time needed. Simpler and cheaper to buy one.

... or improve one. I bought a "Rogue" 100W combo from craigslist. It's a 2-12 combo amp and I got it for $40 because it didn't work.
<snicker> make my day. It has a 100W capable power supply in side, a usable if not pretty wooden case, two speakers that actually work, and a metal chassis that's roomy and easy to work with. I could not have cared less if the silly amplifier worked or not. I commiserated with the owner and said I was glad to get it and take it off his hands, which I was.  $40 is only a few hours of work even flipping burgers. It's far less time than getting out the table saw, saber saw, drills, glue, calipers, rulers and tape, vinyl covering, and having my way with them. Also cheaper than the raw materials, and I got a huge heat sink to boot. Power amp PCBs sometimes don't tell you that you'll burn up the output transistors in milliseconds if they're not on a suitably large heat sink.

Ask me how I know this.   

Frankly, it is very difficult to beat a PCB with one  to four LM3886 power amp chips and a heat sink for making your own power amp. It still leaves you the power supply and cabinet to make/get, but at least the LM3886 will likely work when you power it up.

A scar is your diploma from the university that you're still trying to forget.

[GibsonGM]

Well said, R.G.!  Every time I start up a new tube project, I get into the preamp and then it sort of....dies off.  Due to the large amount of time required, working the power section, finding trafo's and stuff.   Thumbs up for the LM3886! Not tube, but not bad, either.   

If we can keep it simple stupid, maybe we'll have time to design the front end of thing...which really is the same as a stomp box!  Ha.

[njkmonty]

I agree  with the educated.
However putting money costs aside, the challenge and satisfaction of learning to build an amplifier is rewarding.
5 years ago I stumbled across a Diy fuzz face video ( see below)
http://www.youtube.com/watch?v=xOcV-WhX7c4

and was amazed how simple and few parts it has. I learnt a lot from that, began to build more challenging builds etc, learning on the way.
A couple of years from that point, I was in my local Music shop talking to the Electronics Tech asking about how hard it was to build a guitar amp.
He basically said it was almost impossible and just let it go.
Feeling discouraged I still kept looking online. Came across "Metroamp" Marshall clone pdfs which I downloaded, studied the parts etc, how they connected, (while still not having a clue about how it worked).
Then one day I had a engineering friend pop over who was explaining to me about diode rectification etc, which i was having trouble understanding.
I showed him the printed pdf , we looked through it, and i asked him "was it possible?"
His encouragement was all I needed, so i kept researching , came across 18 watt Amp forum, printed everything out I could find and asked many a question.
Now I believe R.G is right in saying that the easy path, is the safe path,and cheap path. No one here wants to have another obituary in this forum.
But if you want to learn , not worried about the budget, are willing to put safety first, and not be in a hurry to fire up the first thing you have soldered together, then go for it.
Forums etc for a Bass amp, may be a little harder to find, but starting at a simple 2 knob amp may be a great stepping stone.

common sense says go the LM3886,  but dont stop there!!
now I know you said solid state,  but all i want to say is, why not a full valve Bass amp?   
It may not be your next build, but I just want to be the one who says you can do it. Just follow all the safety procedures

[R.G.]

I didn't intend to come across as saying "don't do this".

Just "know what you're getting into - it's big, much bigger than it seems at first".

And I have spent much of my life chasing down and mastering skills. I'm not certain knowing how to build a hay loft and why it's in the top of the barn, not the bottom, is all that useful, nor that Clostridium Botulinum spores will survive boiling for many hours, nor how to cut a decent bow out of a sapling will come in handy to me, but then I always also believed that a monstrous mind is a toy forever.   

[njkmonty]

I didn't intend to come across as saying "don't do this".

You didnt! 

All your answers are generally right on the money, even when I dont fully understand them!

[GibsonGM]

Oh heck yes, if you wanna learn amps, go for it!  Sometimes I  even get excited by a 1 power MOSFET thing and will take the time to toss together something that is just fundamentals, to see how it sounds...because that is the fun in this     Just that you can produce more with pedals, IMHO.    But maybe you don't WANT to produce more, but to make the best tube baby you can...

[petemoore]

 
  One reason I would build is to stress relieve all the in/out jacks with wires, this can sometimes be done to the 'relevant' connectors inside the box of an existing 'jack-housing-into-PCB-type-amp].
  SS output at it's best = linear [clean], and powerful [enough for speaker coil control], other stuff like low noise,...by studying and comparing amplifier specifications [most of the 'better' amps of factory and DIY type do pretty much what they advertise], the choice of what to have as a linear amplification should become pretty clear.
  Chassis, heat sinks [hard to machine], induction...makes the schematics may look easy.   
  There is stiff competition from 'what's already out there' for ''Cost Vs. Watt'' SS amps, mass production of big amplifiers does have advantages that can be hard to challenge.
  Many proven layouts started out as one-off experiments, kits are also worth a look.
  I've found it easier to apply multiple smaller amps than 1 huge amp.

[PRR]

> mass production of big amplifiers does have advantages

Moreover the economics of musicians means there's always a good supply of lightly-used power amplifiers, and also broken/rebuildable carcasses which save buying most of the big dumb parts.

[Transmogrifox]

As for safety, you can get 70 watts pretty easily off a 50 Volt rail.  As long as the mains input transformer is properly handled, and your output is <65V, then electric shock is probably not the most eminent danger.  Everything you do in the amp on the low voltage side of the transformer has the following safety concerns:
1)  Arc flash -- if you end up having a large bulk capacitor bank and accidentally short this with a wire or screwdriver, you will get an arc.  It might cause a burn or make something fly in your eye.  Probably you aren't dealing with enough power for serious injury, but still good to be aware that low voltages can still be dangerous even though electric shock is not part of the danger.  Arc flash is usually a more grave danger when you're messing with your electrical panel where the unprotected mains come into the building.
2)  Heat, thermal => fire.  If something is done incorrectly you can start a fire.  Be prepared with a fire extinguisher and an easily accessible power strip that you can switch off. 
3)  As a result of #2 you can get some pretty nasty gases released into the air.  Good to make sure your work space has decent ventilation.

It's good treat the low voltage stuff as if it's could have a fatal bite.  Especially if you're learning as you go.  It's sort of like the gun safety mantra "always assume the gun is loaded and handle it as such".  An unloaded gun won't hurt anybody even if you point it at their head and pull the trigger.  Likewise 50 Volts isn't enough to induce fatal currents into your body, but careless habits result in accidents when somebody forgot to unload the gun, or forgot that certain part of the circuit board actually carried AC power.  We practice these habits to prevent careless behavior when we're dealing with the real stuff.

I know, I got bit pretty good one time on 120AC playing with a wall wart.  I wasn't getting 9V out, so I took it apart and started poking around with it plugged in.  Due to carelessness "oh this side of the board is only 9V" I found myself seeing stars on my work bench.

I think we can all agree we're not trying to scare you away from playing with amplifiers.  Just (like RG emphasized) be aware of what you're getting into.  It can be very rewarding to take on a project like this and succeed.  As stated before, it's not beyond your reach. 

You may want to make yourself a regular troll at one of the amp forums if you start this project.

[anotherjim]

There are electrical safety regulations that have limits for what a "semi-skilled" worker should mess with.
In my part of the world it's this...
175 Volts or more -  Don't.
20 Amps or more short circuit current - Don't.

The 20A limit ought to rule out working on auto electrics, even though that could be only 6 to 24volts.
Plenty of burnt out wrecks in scrapyards from a DIY boombox install.

[ulysses]

amps are pretty awesome to build and experiment with

if you are into overdrive pedals and are looking for more expansive tone digestion then definitely get into amps

theres all sorts of goodies like different speakers / output transformers / tubes / spring reverbs / tube vibratos etc etc that you dont get exposure to in pedals + you get all the pedal goodies like tone blocks and tube overdrive (opamp/tranny overdrive)

you get caught up tinkering in amps to make them just right for you - awesome way to spend weeks of your time

i made the mojotone tweed deluxe (awesome) a couple of weeks ago and also spec'd to original condition a reissue marshall bluesbreaker and a vox ac15h1tv

i would suggest buying an amp kit which makes it super easy to start. there are plenty of good suppliers of kits out there!

cheers

edit- i should note that there are dangerous voltages in amps - never put your hands in a live amp! and learn how to drain caps before you put your hands in amp that has been live! im sure RG or someone has a guide to safety for working with guitar amps! read it!

[Greenmachine]

Build a light bulb thingy.  Its a 100 watt bulb mounted on a box with a plug and socket. Plug this into the wall. Plug the amp into the bulb unit.  If there's a short in the amp somewhere, the bulb will light up 100%.  Shut off the amp. Unplug from wall. Discharge filter caps and begin troubleshooting.

[petemoore]

  Look for fried amps, generally go for naught when blown [or otherwise], often the old ones are easy to rework because 2/3rds or more of the chassis is open space.
  Blown output transistors is fairly common, often the iron works + chassis, hardware...
  A classy cabinet and new front panel can hide the chassis 'wrestling' industrial equipment contended with. 
 

[amptramp]

Building from scratch is fine if you really want a long project.  I have been building stuff for ages and I would suggest getting a used public address system to convert into a guitar amp first.  Why?  Because the guitar amp manufacturers assume limited use and they use components up to the maximum rated stress and beyond.  A storecast PA system is expected to run 12 yours a day, seven days a week without attention for years and is rated conservatively.  My taste runs to tube amps and I have Muzak 920B ($15 as purchased), a Stromberg-Carlson 207 and a Bogen Challenger CH-8 PA amps, the latter one acquired at a garage sale last Saturday for $10 with matching microphone.  The Muzak uses a pair of push-pull 6L6GC's to get 15 watts and there is a resistor from the power transformer centre tap to ground that can be shorted out to give 20 watts.  Very conservative for a tube pair that would be good for 30 watts in an instrument amplifier.

If you decide you like the experience, then go for a scratch build but use conservative PA system design rules for the power stages combined with whatever low-level circuitry is used in your favourite guitar amp.  Many of them have features like tremolo and other effects built in.

[Satan Of Saturn]

Thanx for all those comments... I'm from India, Kolkata... a real @#$%ed up city for musicians where Marshall stacks or any normal tube amp would cost more than my dad's one month's salary... a 5 watt Blackstar tube would cost Rs.32000!!!! pretty costly. I'm not planning to make any tube since it needs time, maintenance and most importantly, money...

I need some schematic design (or PCB layout would be great) which will be good enough with bass... using a 6 string bass. I'll make the amp head and buy some speaker cabinets  from the market. I've cloned some pedals but dont have any idea about amps... those impedance calculation kills me... :-(

[R.G.]

Power amps are really power *supplies* with some electronics stuff attached to let the power out in a controlled way. They generate a lot of waste heat, which must be eliminated or the parts will overheat and die.

The most expensive parts of a power amp are generally the enclosure, chassis, power transformer, heat sinks, main power filter capacitors, and then the power transistors or power ICs. Everything else is much lower cost and for a first order estimate of cost can be ignored or lumped in as "oh, yeah, I have to put in an amplifier."

Since you have not built a power amplifier before, here's some things to get you started:
This power transformer will drive two LM3886 power amplifiers to about 50W each:  http://www.antekinc.com/an-2222-200va-22v-transformer/
It is an incredible deal for the price, at least here in the USA. Don't know about where you are.

Here's a power amp kit that is pre-assembled and will do the job:
http://www.ebay.com/itm/HIFI-YJ-LM3886-68W-68W-stereo-amplifier-board-3pcs-total-/300804350433?pt=US_Amplifier_Parts_Components&hash=item46095621e1

It is remarkably low priced for what you get, and might save you quite a bit of time.

This is a reasonably good heat sink for a 50-60W amplifier like the ones above:
http://www.ebay.com/itm/Aluminum-HEAT-SINK-FOR-LM3886-TDA7293-Amplifier-Board-/220697781907?pt=US_Amplifier_Parts_Components&hash=item33629ce693
It is a remarkably good deal for the price if you do not have access to industrial surplus parts to repurpose.

These major parts are the working pieces. They still leave the issues of a metal chassis, an overall outer case for making it rugged, and the issue of mains AC power wiring being dangerous.

[Satan Of Saturn]

Thanx R.G, those links are interesting. would learn a few things for sure. I was searching for some details on internet and I found schematic of Marshall JMP 2195 lead and bass 100 Watt. I think this would work fine for me now... for my home practice and jamming at our jampads.

http://elektrotanya.com/PREVIEWS/63463243/23432455/marshall/marshall_jmp-2195.pdf_1.png

But I think there's something wrong with 'earth' line at bottom right... it shows that it has been connected with +40V :-D that is definitely wrong i think.
wont be a big problem in designing a PCB for that. coz its a basic transistor type amp. Just a bit confused with the power supply.. I mean what should be the transformer rating? should it be 40-0-40 with 3A. I'll use 2*12" cabinet. Should I use a regulated voltage source to get exact 40V? or just rectifier output with heavy filtering would do?