DIY distortion pedals.

  • Thread starter Thread starter Steenamaroo
  • Start date Start date
Pretty bad really. Have you actually tried running a stompbox off of "any old" wallwart?

Any amplifier circuit - from a simple unity vain buffer to a distortion pedal to a hi-fi amp - works by modulating some supply voltage in proportion to the input signal. It takes the supply voltage and turns it up or down to follow the wiggles in the input wave. Now, if that supply voltage is already wiggling on its own, what do you suppose you hear at the output?

You seem to be disparaging batteries, but really they are almost ideal. Aside maybe from a tiny bit of thermal noise they are perfect pure DC. No wiggles period. A wallwart takes the wall power - wiggling back and forth either 50 or 60 times per second - uses a set of diodes to force it to wiggle only one way (but at twice the frequency), and then uses a capacitor as basically a low pass filter to try to knock down the wiggles to whatever the designer feels is "close enough" to perfectly flat. Some get closer than others.

Well designed pedals which expect to run off wallwart power will include some semblance of filtering inside to attempt to make up for deficiencies in the supply. The problem is, though, that in order to get enough filtering at a low enough frequency without introducing too much series resistance you need a really big frickin cap. And by big I mean physically large. The ones I use in my DIY pedal distribution boxes are almost as big as my thumb. It's tough to fit that into a typical wallwart or stompbox.
 
Very informative answer. Thanks for that.

Who knows, maybe I'll just run it on batteries?! lol.


Does the same apply for switch mode wall warts like this?

(blackstar is en route - Got a tracking number today)
 
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It is worth mentioning that a great many power amps actually run unregulated PSUs. Unregulated in the sense that the AC from the power transformer is rectified and smoothed by the reservoir capacitors (sometimes lots of them), but there is often no active regulation beyond that. (Some amps use a combination - regulated supplies at the voltage amplification stages, and unregulated at the current amplification stage).

My home power amplifier uses a standard unregulated power supply and, even at high output, harmonic distortion is still less than 0.01%.

If you want, just use an AC wall-wart (say 9 to 12V) and work from that. Rectify it and smooth inside the box and regulate as desired

Given that the Deacy is all about distortion, you lose nothing by experimenting a bit.
 
Well I did a bit of reading and found a few sources saying that a decent regulated power supply will not be perfect (obviously), but should be adequate in most situations.
I think I'd be happy enough to try that.
Perhaps I'll fit a battery socket too far comparison.
 
DANG PAUL!!!!
I just got around to reading this thread - How's the thumb?
 
Ain't so bad. Thanks for asking.
Got the stitches out on Friday and it wasn't just as well healed as I thought, but I guess a few more days will do it.
:thumbs up:
 
AIUI, regulation doesn't do a whole lot more than to limit the maximum voltage that gets through to the circuit, more or less independent of load. You put more V into the regulator than you need - up to the maximum the reg can handle - and it puts out exactly what you want. The rest gets burned off as heat. If you put less V into the reg you'll either get less out or nothing at all.

If your circuit has components with tight voltage limits and you insist on running it close to those limits then you need regulation. If, on the other hand, it will work without exploding over a reasonable range of voltages then there's no reason to bother. Computer PSUs are regulated, as are those for most digital effects. Distortion pedals and guitar amps probably don't need it.
 
Thanks again for the info, ashcat.
I'll just use what I have and see what happens.
 
@Steenamaroo:

Might be good idea to get a Deacy thread up and running to separate out chat about your original post, and stuff relating to the Deacy? You are now committed to the Deacy build after all :cool:
 
Cheers Paul.
I was holding off till the blackstar arrives so I can try and test the treble booster and record some clips.
Touch wood, that should be tomorrow. It'll be a long wait though. Santa's bringing the kit.
 
While I wouldn't consider myself an authority on the subject, and I don't know how much of this you already know, I'm bored at work, so...

If you look at the specs on an unregulated wallwart you'll see that it gives a voltage - say 9VDC - and a current spec - let's say 1A to keep the math simple. This doesn't mean that it will push 1A at 9V through whatever is connected. Your device will draw the current it needs and the voltage will float to where it needs to go to provide that. If you put your meter (which wants very little current) across this supply you might see that it puts out 12VDC or more. As the load or current draw increases the voltage will drop. Ohm's Law is. It will only give you exactly 9V out when you draw exactly 1A. Try to pull more than 1A through and the voltage will continue to sag below 9V until some component in the wallwart decides it's working too hard and lets out its magic smoke.

A regulated PSU with the same stats will give you exactly 9V no matter how much current you ask it for up to 1A and then either burn up or (preferably) shut down.

Now, when I said that a distortion pedal "probably doesn't need it" its because most of the components in most distortion pedals can handle something like 12V without thinking twice. There might be caps in there rated as low as 16V, but I wouldn't sweat much with anything labeled at 9VDC. But there might be some subtle change in the sound based on the supply voltage. Many of these things work by attempting and failing to put out more voltage than the supply can give. Remember how I said that amplifiers modulate the power supply? Well what do you suppose happens if say you put in a 1V signal and try to apply 10x gain? It wants to put out 10V, but it's only got 9 to give. The output can't follow the input in a linear manner and you get distortion. But what if that same circuit was running off of an unregulated supply, and getting 12V? Your distortion box becomes a clean boost! Many people dig running fuzz boxes at less than 9V in order to get more crunch. To be fair, though, many of these things really want to put out hundreds of volts, so a V here or there probably doesn't make a huge difference.


One more thing. DC supplies always include one more very important spec: polarity. This is the one which will kill your device dead if you mismatch them. Most commercial pedals use the "Boss standard" where the outside barrel is positive and the inside pin is negative. Most wallwarts not specifically meant for stompboxes go the other way. There is an easy way to protect against reverse polarity in a pedal. Boss pedals even have all the parts to do it. Unfortunately these are installed in such a way that they will only protect for a very brief moment before failing. They protect Boss's warranty Dept by making it obvious that you didn't use the official Boss brand adapter!
 
I was aware of the difference between reg and unreg, and also of polarity, but I didn't know what the consequences of powering a fuzz with unregulated DC were.

I also didn't know the reason that boss reverse polarity, so thanks again. :)


Is it fair to say that Boss (and similar) power supplies are of a reasonably high standard for their application?
Maybe I could just pick up one of those.

dscn3108.webp
 
dang HOF, me too, how did I miss a new thread in DIY? Good on you. Good point too from (Ashit?) about mains and all that. My only truck with batteries is the white acidy stuff that accumulates when I forget to change them!!!!! One caveat on that though, I had some hum in a reverb and used a couple of 9v batteries to give it a quick bipolar power supply to eliminate the PSU as the cause of hum.

One note about regulation (and I am clearly an amateur at this -- so no flames please) the guy in Australia (has a bunch of DIY stuff) states the 78xx and 79xx series regulators can be noisy and recommends the 3x7 regulators instead.
 
Hey Jinn. Thanks for chiming in.

I'm glad everyone added their info about PSUs. Some of it I knew; Some of it I didn't.


Given the nature of this project and the fact that I'm trying to keep it simple, I'll arm it for batteries and a 9vDC jack input.

At least then I can compare batteries to wall warts and if there's a problem I'll deal with it then.


I'm gona hit the charity shops for an oul 6" hifi speaker.
If any of you UKers have a scrap one, feel free to hit me up. 4 ohms preferred.
 
Blue Jinn said:
One note about regulation (and I am clearly an amateur at this -- so no flames please) the guy in Australia (has a bunch of DIY stuff) states the 78xx and 79xx series regulators can be noisy and recommends the 3x7 regulators instead.
Click to expand...

That will be Rod Elliott (Elliott Sound Products), a champion of "rational" audio.

It is generally accepted that the 3x7 regulators are quieter than the 78xx and 79xx fixed regulators. However, extreme PSU quietness is probably more important in microphone pre-amplifiers or A to D converters. (Of this, this creates a whole realm of tweakery for audiophiles...).

It is hardly any more effort to use the 3x7 regs, but some simple math is needed to work out the appropriate resistor network.
 
Right, everybody chill out.
I'm gona run it on a honda 90 engine and a dynamo from a bicycle lamp.
 
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