weird crybaby scratching problem

[pinkjimiphoton]

hi guys,
i slapped together a crybaby out of parts for a friend last nite that needed one, but ran into a bizzarre problem...

it was a gcb95, earlier style replacement board that someone had removed the input buffer from...the gain resistor of q1 was replaced with a trimmer by whomever owned it before, i like it cranked (no surprise)

but here's my question...could the CIRCUIT make scratching noises from having the gain too far off?

i thought it was a bad pot...i replaced it. twice. i even took the pots out of two cb's i KNOW are good...

and all of 'em scratch, but only in this one stupid circuit. any ideas?

he loves the thing, into enough distortion it's pretty much inaudible, but it's driving ME nuts. gotta figure it out!

[John Lyons]

I had a problem like this. I tried a 220pf cap to ground from the output.
(Right off the hot side of the pot)
Seems odd to do at the output but it cured the pedal. I chalked it up to some kind of
oscillation issue.... Try it out, simple enough.

[KBG]

crying babies will sometimes scratch themselves and should have their fingernails trimmed

[joegagan]

this can also be a trace on the board, or a connection that is ever so slightly intermittent. try the old aron nelson trick of moving the board manually while you listen for noises. poke around with a stick, etc. with a wah it is a little tricky.  i have solved this very problem this way before as well.

there can also be some dc on the trace that shouldn't be there. are the caps good?

[R.G.]

there can also be some dc on the trace that shouldn't be there. are the caps good?

... and we have a winner for the next step in debug. Check for DC on the wiper. Could be coming from either Q1 collector or Q2 base.

[Earthscum]

<smacks forehead>

Just cured something I was fighting. Thnx.

[pinkjimiphoton]

now i gotta just get it back from him!! he love the thing, it makes me crazy, but he doesn't seem to care!!

good tips, i will check it out if i can get the sucker back from him...he likes a lot of distortion, and it's not really noticeable other than clean..so maybe i'm stressing too much.

[John Lyons]

Oh, just remembered that in my case the "scratch" was only at one small point in the rotation.
So basically showed up as a sort of "tick" near the tow down position. So probably not DC in this case.

[pinkjimiphoton]

that's kinda what was happening john, in this case at a couple "spots"  in the toe down position.
what made me think circuit was cuz it did it regardless of pot, seemed more freqency dependent.