big muff sustain control crackling...

[gutsofgold]

Is this normal? My buddies homemade big muff and my black Russian reissue both crackle when the sustain knob is adjusted. Could it be my amp? Do all Big muffs suffer from this?

[Boogdish]

I just finished a DIY Big Muff and I didn't experience this.

[tskullt]

Check for voltage at the offending pot.  You probably have a stray trace or bridge...

(I had a booster do that!)
m.

[raulgrell]

Crackling is caused by DC voltage going through the pot. Check for any caps that might be badly soldered/burnt, or a solder bridge...

[gutsofgold]

Ok so I noticed my board wasn't etched all that well. There were a few breaks in lines and such that may or may not have been a problem. So I etched another one with much better quality, it is perfect and I repopulated it. The sustain pot no longer crackles but now the tone pot does. I replaced the tone pot completely and still got the crackle so the problem must lie somewhere on the board.

Next I will check the capacitors, I'm looking at C10, C11, and C12 as they are all directly connected to the tone pot someway. Any other things I should check out?

http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf

[gutsofgold]

there's voltage at both the sustain and tone pots and if I take out the last transistor Q4, the problem goes away. I've tried a new transistor there and the problem comes back. The traces are perfectly fine, wiring is ok, I'm starting to think it's the blend circuit I added to this.

[kurtlives]

Crackling is caused by DC voltage going through the pot. Check for any caps that might be badly soldered/burnt, or a solder bridge...

Yep

Check for a bad cap, probbly the coupling between gain stages.

You could add a cap is series to filter the unwanted DC out.

[gutsofgold]

so I replaced nearly every cap on the board, tried plenty of different transistors, bypassed the blend circuit, the problem still exists!!! I've settled on ghosts inhabiting the circuit.

If I was to add a resistor in series to filter out the dc, what lug of the pot would I go to and what size cap? that would be really awesome if it worked...thanks!

[kurtlives]

Check the cap in series with the third lug of the gain pot. Correct polarity?

[gutsofgold]

C3 on that layout I posted up top? If so... that's a film cap... no polarity

[kurtlives]

Ya C3...I just googled BMP schem...I couldn't be bothered by the versions so the first one I clicked was a NYC one (I think) and it has a 1mF cap.

[gutsofgold]

the fact that the problem goes away when Q4 is removed has me intrigued but i just can't quite place it.