Big Muff Pi repair

[Yazoo]

I am trying to repair a Big Muff Pi, a Fran Blanche version, EC3003-A. The tone pot is scratchy. So far I have replaced all the aluminium electrolytic caps. The pot had already been replaced but it was still scratchy so I replaced it again. It is still scratchy! I the measured it and get 3.5V on pin 1 of the pot. The schematic shows a capacitor to pin 3 of the pot and a resistor to pin 1, both connected to the collector of the 2N5088 transistor. Is the scratchiness normal or is there something else going on? The schematic is available here:
http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html

[CheapPedalCollector]

That's because there's is no DC blocking cap between stage 3 and the tone control, it's a bug in the big muff. There is DC across the pot so it will always be scratchy.

Adding one will change how it sounds because it alters the collector bias.

[Yazoo]

Thanks, I'll leave it as it is.

[antonis]

Adding one will change how it sounds because it alters the collector bias.

Not really..

Without that cap, Q3 Collector equivalent resistance is 9k35 (10k//144k) where with DC blocking cap will be 10k..
The above 6.5% open-loop gain reduction has a negligible involvement in Q3 stage closed-loop gain which is set by G/(1+βG), where G = Collector resistance divided by Emitter resistance plus intrinsic Emitter resistance (10k / 390+55) and β = Series resistance divided by Feedback resistance (10k/470k)..

@Yazoo: As long as DC blocking cap is much bigger than Tonestack caps bigger value (100nF or bigger in your case), you shouldn't experience any issue..

[Yazoo]

I went back and decided to check for bad solder joints. Sure enough there were 2 really bad dry solder joints where wires were connected - FROM FACTORY. Once I redid these, the noise disappeared. No problems with the tone pot now.

I don't like the way the way EHX did the wiring on these pedals. They tack the wires on to the solder points of other components, no separate holes for the wires.