This thing is such a piece of shit.
I was feeling sorry for myself, so I thought I’d “accomplish” something by making a fuzz pedal. I’ve now been doing this stuff for long enough that I have somewhat of a critical mass of materials, so I have everything I need to make a pretty simple circuit without ordering more things (unless it’s using some weird IC or a whalebone or something). So because there’s no time impediment (waiting for a part to arrive, etc), often I’ll think “hey, I’ll just make a quick little pedal”…and then the next thing I know, it’s 4AM, I’m dizzy from solder fumes, and I’ve made a pedal I don’t need that’s in questionable operation because I’m tired and making mistakes… and it’s generally stupid, is what I’m saying.
Anyway, here’s my latest trainwreck.
I wanted a fuzz pedal because it seems like they’re one of the most common pedals people make, and I hadn’t made one yet, and there was what seemed to be a pretty simple one in Craig Anderton’s Electronic Projects for Musicians.
This is another great example of me not learning: I had previously expressed…well, distrust of his book. I know the book is very much canon in this hobby, but the one circuit I had done before had been a mess (due to mistakes on his part and what I’d consider generally shitty design). So, I could have chosen one of the infinite other fuzz circuits from the internet that people have put through the ringer, fixed errors, and optimized, buuuut… of course I went with the bad idea. Here’s the schematic:
So, it’s basically based on using an op amp as a comparator, which compares the incoming signal to a reference voltage, and gives a high output if it’s above the threshold, and low if it’s below. Here’s the little illustration CA uses:
And mine does this exactly. I input a sin wave from my cheapo function generator into it and looked at the output with my cheapo scope, and, yep, it does that. Whoooo whee.
Here’s the thing: it sounds like GARBAGE. It sounds so bad I literally can’t imagine wanting to use it in any song. There’s what I’d consider a small subtlety to this though. Here’s the main reason, I think: it essentially acts as a “gate”, in addition to a distorter. The intended purpose of the pedal is to do what I said above, to turn a smoother waveform into a square-like one, which will naturally have a rougher sound. For example, if you have a large input, say, a sine wave, it essentially turns it into a sort of square wave, like so:
But of course, you’re not usually doing this on most instruments, putting in a constant sine wave. Most of the time, for example on a guitar, you pluck it, there’s an “attack”, a short burst of signal, and then it decays. Keep in mind that the signal is still oscillating, but it’s really an oscillating signal inside a decaying “envelope”.
However… if you think about what that would do in this comparator circuit:
As you can see, the threshold/comparator does what it was intended to do (turn that smooth oscillating waveform into a square-like one), but it also has another effect, the “gating” effect, where, because the whole signal is below the threshold, it has zero output. Now there are actual situations where you would want a gate, but it sounds pretty bad here. The effect is that, if you pluck it, it will play, with distortion, for a little, decay, and then abruptly just turn off. It honestly sounds really bad.
I’m not even including a pic of the build, because there’s basically nothing to see. It’s an op amp and a couple diodes. Too exciting.
There’s one more fun quirk this circuit has, that CA even acknowledges in the book:
And he’s right. If you have it set to about the center (basically meaning, so the threshold is about zero), it pops and makes awful fucking demon noises. I’m gonna guess at the reason, but this is pure speculation: there’s always some inherent noise in these circuits. The first op amp stage is just acting as an amplifier, so random stuff like RF noise, instabilities, etc, are always there, but small. So normally this stuff probably wouldn’t be audible at all, or really really quiet. However, if you make the threshold really low, it makes this noise occasionally go over the threshold and get turned into the same height signal that your actual playing would probably get turned into. However, it’s also not just a regular audio frequencies getting turned into that. It’s noise, so it can probably be at any number of frequencies. So maybe you have some low frequency RF noise, and some small percent of it make it over the threshold (essentially downsampling the frequency), so you end up with an audible screech.
Or I could be full of shit. I dunno, man.