The "Forum Amp" design thread

[Taylor]

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.

[arawn]

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.

[markeebee]

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    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.

[markeebee]

Immortality, I meant.

But on the other hand....

[slacker]

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.

[cab42]

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

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

[Taylor]

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.

[jkokura]

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.

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

[Brymus]

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
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  
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 

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.

[Brymus]

@ 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.

[Morocotopo]

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.

[tuckster]

Regarding the power supply, are laptop ones bipolar?

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

[armstrom]

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

[culturejam]

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?

[Brymus]

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.

[culturejam]

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.

[Taylor]

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?

[jkokura]

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

[Derringer]

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

[Earthscum]

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!