Wah pops mid-sweep

[KWilcox]

Here's a weird one - I've got a GCB95 which I've modded to sort of in between a GCB95 and a maestro boomerang. Now what's boggling my mind, is that if I have any effects boxes AFTER it, it will scratch/pop almost exactly in the middle of its sweep (very briefly but quite loud). If I use the wah alone, or use any effects before it, then it works flawlessly... it's not a scratchy pot. Besides a few resistor/capacitor component changes, the only difference is that the zener diode in the power section is missing but I don't see any reason for that to affect the signal output. this makes noooo sense to me, and I'm really hoping someone else is better educated...

thanks for any ideas!

[aron]

>will scratch/pop almost exactly in the middle of its sweep (very briefly but quite loud).

I can't imagine other than a bad pot what this could be. I guess you could sub another pot temporarily in place and sweep it with the pedals attached to see if it is the pot. I guess you could record the output into a computer even without the extra pedals just to see if there are any weird pops etc... Record and look at the waveform in a sequencer.

[tcobretti]

I had this happen when I put a buffer after both of my wahs, one a Boomer and one a Vox.  It drive me crazy.  I had to pull the buffers.  I think it happens frequently but that most people don't notice it through the distortion/fuzz.  Are the effects after the wah buffered?

[KWilcox]

I'm certain it's not the pot, becauses the possibility of it not being the pot confused me so much that I put an effect after it, and then removed that effect, about a dozen times making sure it repeatably made the scratch come back/go away/come back/go away/come back/go away ... it's also a brand new pot, haha.

tcobretti - yes! the pedal's I'm putting after it are buffered. I've tried putting BOSS pedals after it and also a 2nd crybaby (also GCB95) that I have. Both cause it... so I guess you might be right in saying that it has to do with buffering the output. but... what the heck?!? I thought the input of any amp is pretty much buffered as well? yet they don't make it happen  ...

My other GCB-95 is stock and doesn't do this... and it's consitently happening between two separate amps (small solid state acoustic amp, and a fender blues deluxe) I guess I'll wait a bit longer before I start reverting my modded one piece by piece... 

Thanks for the input!

[John Lyons]

Amps inputs aren't buffered ( at least not that I know of) , high impedance yes.
I have a Roger mayer Wah that has this same symptom.
It was set up as non true bypass and then changed to true bypass.

So what to do. No buffered output?
Guess I should try it back as buffered/non true bypass.

john

[KWilcox]

well. this weekend I'll be trying to figure this out... first try a different pot to make sure it isn't some weird property of the new hot potz II (heck I don't know... static buildup!?) .. then start reverting transistors, caps and resistors... will post any results I figure out.

[KWilcox]

I dare say... I had put MPSA44's in instead of the stock MPSA18's ... after reverting back to MPSA18's, the noise seems to have gone away. I'd really like to figure out why the lower gain (correct?) 44's might be the cause of that behaviour...

Now I have another issue - the wah is overdriving when I strum it hard  (i have a slightly higher than average output guitar) anyone got any suggestions about curing that? 

[tcobretti]

Raise the value of the 68k resistor that is the first component after the input.  I'd sub in a 100k or 200k trimpot and tweak to taste.

[Paul Perry (Frostwave)]

All I can think, is that the bias of something is being varied as you move past that point, and the sudden current change is making the pop.
I'm not familiar with the circuit - do any bias elements change as the pot is swept?

[stobiepole]

I found using film caps instead of polar electro caps caused some popping problems - I'm talking about the caps attached to the pot, before and after. I think using polarised caps helps...

Chris