Green Russian (Big Muff Pi) - Finished, but still a bit of noise

[jfrabat]

Hi, guys.  I just finished my Big Muff Pi Green Russian clone (it is actually a PCB from BYOC, instructions here).  Everything is working, but even with my humbuckers, the pedal is still humming a bit.  I was wondering if there is anything to do about that (my guess is that with some cap filters I may get away from that hum, right?).  I also own a coil PRS, and I did not even try it with that one as that one hums with no pedal!

Anyway, here's how the pedal looks like:




This picture was taken before the pedal was finished; the wrong sized resistor and the missing resistor are not an issue any more.


Taken at the same time as the above; same 2 issues.

Sample of the hum:

Any advice?

[PRR]

Temporarily tack in a battery. Does it still hum?

[jfrabat]

Temporarily tack in a battery. Does it still hum?

A lot less.  Even with the pedal off, you can hear a slight hum, which is obviously magnified when the pedal is on.  With a battery, the hum is much lower volume, and another tone (deeper).  By the way, I am sad to report I accidentally burned out the LED's during this test (did not notice they were shorting out, which turned them on while the pedal was off)...  Will need to replace the ring now...   

[pokus]

Hey,
first of all I would add the 20uF electrolytic cap between + and gnd, like the original Big Muff do.
If hum is still there you can slightly increase the value of the two caps int the feedback paths. Normally those are the ceramic ones with about 500pF. Maybe try one or two values higher (680 or 820pF) or even more higher, but this will cut some of your wanted high frequencies too.

[antonis]

first of all I would add the 20uF electrolytic cap between + and gnd,

No shunt cap (of any value) does nothing by its own..
It needs a series resistor to form a low pass filter - of course you can count on PS internal impedance for that but those impendaces are practicaly negligible so you'll need an almost infinite capacitance..

P.S.
<copying Jack's comment - with no written permission..  >
http://www.muzique.com/lab/filter.htm

I cannot tell you how many times I've seen it said in an effects forum that wall-wart adapters* are poorly filtered if at all. This is oft-repeated misinformation that can end up confusing a beginning builder. I've disassembled many of the little black dc power packs and every single one of them had 1000uF of capacitance as a filter! That is why I find it amusing when some well-meaning enthusiast (who has never disassembled one) recommends merely adding 100uF or 220uF to the power supply as a means of making it more quiet. That's not too effective by itself.