Fuzz picking up radio interference and hiss

[rogeryu_ph]

Guys,
How to  isolate this interference and hissing sound maybe some of you has encounter this problem. This interference come out when fuzz pot (1k) at max and when vol pot (500k)is at max hiss sound is apparent. Once I read in an article saying use 100pf cap between input signal and ground is the answer to eliminate interference but i'm not sure. About hissing sound also what's the remedy... Thanks 

Roger

[plankspank]

For radio interference, it's always a good idea to insert a resistor before the Crf Cap (between signal input and the ungrounded end of the 100pf). This will prevent your guitar inpedance from combining with the Crf cap to act as an RC tuner).
As for the hiss, what circuit are you using? Germanium transistors are notoriously "hissy" especially when run at maximum gain as you describe.

[rogeryu_ph]

Thanks for the reply plankspank. Germanium PNP with neg ground from Tonepad project.
Hiss sound: I tame it by changing pot 500k with pot 100k and change the 33k resistor with 15k just to get Q2 collector 4.5v.

RF interference:I will series a resistor to one lead of 100pf then solder the resistor to input circuit and then ther other cap lead solder to the ground of the circuit? What resistor value?


Again thanks
Roger

[Paul Marossy]

What resistor value?

47pF will usually do it.

[R.G.]

Germanium PNP with neg ground from Tonepad project.

I just keep telling people not to do this and they keep doing it anyway and showing up here with "It doesn't work very well" issues.

(a) Internal RF oscillation often shows up in the output as a kind of angry hissing.
(b) Poor grounding - like with the inverted ground situation you have - often makes RF pickup worse.

Negative ground PNP distortions are a bad idea. They often have intractible problems with oscillation. Just because a web site shows you how to invert the ground doesn't mean it will work well.

[rogeryu_ph]

Thanks R.G. i just wanna get away with using seperate power supply for this. But I thinks it's working, I was able to  get the FUZZ TONE vintage sound from 1/4 of the vol and almost full to the gain but if  the vol is max hiss sound is apparent and on gain is max RFI can be heard. But for the moment setting is already loud enough and I need to set my amp vol to 1/4 only. I think I don't need to go to full or even 3/4 vol of the pedal anymore but the gain pot is a must co'z turning it down even a little bit fuzz sound will be weak. I used it with my twinDUCTOR wah sound promising. Still I'll be needing your advise on this R.G. i'll may PM you and thanks again.

Thanks Paul, Congratulation on your boomerang am I right? And GP feature is a reward to your hard works and grateful shares you have done also to you R.G. yes indeed. I have 2 questions to you, first I already incorporate a trimmer pot 50k on the input as fuller suggest do I still need to use resistor series with cap 47pf or the cap only will do? Second, your volume retrofit article you use with your Enie ball is linear or audio? I never came accross with ernie ball. I was planning to do the same project for my wah which is somewhat little scratchy I heard. If not does the circuit can? my wah pot is already audio log 100k A.

Roger