"Phantom" background fuzz in op-amp Big Muff

[edvard]

Many years ago (1993 or so), I built my first pedal; an op-amp Big Muff from photocopies of an original that a friend had, so I know the PCB layout is good.  What's happening is that if I play very quietly or my hand brushes across the strings or something, I hear what sounds like a full-on fuzz effect very low volume in the background.  When I do full-on strumming or playing, of course it gets drowned out, but I still notice "in-between" notes and it's bothering me.  I don't know if it's something that just started happening, or I never noticed it before.

My question is, does anybody else have this? Like, it's just something that happens with this circuit?  I probably just need to check my soldering, or build a new one with better traces, as this one is pretty scary, to be honest.

[GibsonGM]

Without more to go on, it sounds like there is some sort of coupling occurring inside the circuit. Somewhere, a wire could cross somewhere it shouldn't, and its signal is 'being picked up' in a place it doesn't belong.  Or, a circuit board trace may be too close to another or located somewhere it shouldn't. Could even be something wrong with the switch wiring.  Or pot wiring/routing (if existent).

The topic of coupling is pretty intensive, and too much to get across easily.  Suffice to say as a layman, if 2 'things' carrying signal are too close together, they can form a capacitor and allow signal to bleed from one point to another. There is another way this works, except that it is inductive in nature (magnetic field...emf coupling).   It is cured by 'proper' signal path routing, and sometimes by using bypass caps to send higher, unwanted junk to ground.

Messing around with any loose wiring to see if it changes might reveal more, as would examining the switch connections and routing of wires.  And always be sure grounds are as they should be, since this may also be a path for 'off' signal conditions.

[pinkjimiphoton]

you gotta bad opamp or a partially shorted cap.
check for dc on both sides of all the caps, and if the jelly bean is socketed, try another. i've seen this happen a lot of times, its always one or the other causing it. you'll sort it out.

[edvard]

Tried swapping op-amps (I gots plenty) and no change.  Now, maybe I'm doing this wrong, so what do you mean by "check for DC on both sides of all caps"?  I put probes on both sides of all the caps.  Some registered 2.43 to 3.something volts, one said 7.2v, and another said .214v. Only one cap showed 0.00v. Did I do it wrong?  It can't be that all the caps are shorted...