FuZz: Hiss/white noise when guitar's turned down.

[John Lyons]

When I turn down my guitar all the way I get a huge surge of hiss/white noise.



With the texture pot turned down to 3/4 it goes away. With the guitar turned
up slightly it goes away. I would normally think this was oscillation but with
cap to ground at the input it remains. Can't figure it out. Ideas?

[GibsonGM]

I've seen diodes configured as a noise source for testing purposes (ham radio stuff); maybe that 1N4148 is doing that, and somehow your volume pot is either allowing the SNR to increase, or is actually involved with generating noise?
Just a guess....

[petemoore]

 Try different cable/guitar to see where ___or if...
 Perhaps after trying this still won't make sense but it might help isolate or explain the phenomenon the system is experiencing.

[John Lyons]

Yeah, I was just fooling with it and it is the diode.
I put in a feedback resistor instead and it behaves now.
Unfortunetly it changes the way the circuit sounds...
But I got something better now. 

thanks chaps.

[GibsonGM]

Wow, I got something right??  LOL

[John Lyons]

You will leave the temple soon grasshopper. 

[Brymus]

That pedal must be insanely loud ?

[John Lyons]

"If it's too loud you're too old? "   

No it's not that loud. I like a hot output though.
It's got an EQ section that absorbs some level...

[earthtonesaudio]

Even though the problem seems to be solved, I'd still like to know more about your setup.  I sometimes get a similar problem with high gain stuff. 

Is your guitar's volume control wired in the standard way or does it use Gibson-style "independent" wiring?

These two ways of wiring the volume control interact very differently with effect inputs.  With the common voltage divider, you get pickup loading at max. volume, and shunt to ground at min. volume.  With "independent" wiring, you get the same pickup loading at max. volume but at min. volume you get just the resistance of the volume pot (which is usually a high value like 500k or 1M).

A lot of times I've found that the inductance of the guitar pickup is enough to stop a circuit from oscillating, but backing off the volume slightly puts in enough series resistance that the circuit is able to oscillate.

[John Lyons]

I mainly use a strat but I tried this circuit out on the les paul to be sure.
I don't think it's oscilation since I put a .1 cap to ground at the input and it didn't stop it.
(guitar volume off) but when I pulled the input wire off it wa quiet...so...