Question about the Fuzz Central Axis Face silicon fuzz.

[Nocaster Cat]

I recently built the Fuzz Central Axis Face silicon fuzz minus the smooth control. I like the way the pedal sounds but if the pedal is engaged and I roll down my guitar's volume I get white noise (for lack of a better term) and as soon as I roll the volume back up a hair it goes away. The only parts substitution I made was a regular ceramic 100pf cap instead of the silver mica that Fuzz Central calls for. I was wondering if anyone else has run into this issue? Would switching to a silver mica cap fix this (I don't have any on hand at the moment). Any insight would be greatly appreciated, thanks.

[Gus]

First
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
Voltages of the transistors might be some help.
Next a link is good, is this the circuit?
http://fuzzcentral.ssguitar.com/axisface.php

IMO you don't need the 100pf the .033uf across the 1.2K should be enought.  Remove the 100pf and check for noise. 




   

[Nocaster Cat]

First
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
Voltages of the transistors might be some help.

Thanks Gus. I believe the voltages are in line but will check and post. The pedal works fine (very well in fact) except for the noise when the guitar's volume pot is all the way down which is why I skipped over the general troubleshooting questionaire.

Next a link is good, is this the circuit?
http://fuzzcentral.ssguitar.com/axisface.php

IMO you don't need the 100pf the .033uf across the 1.2K should be enought.  Remove the 100pf and check for noise.

Yes, that's the one (sorry, I should have linked  ). I will pull the cap and check again. I couldn't sleep last night so I ran a full search on the term "Axis" and found a post from years ago that sounded like the same issue I am having. The solution then was the BD139 was the culprit and while swapping that out cured the noise, it also tanked the sound of the pedal.

I will take measurements, try pulling the cap and get back. Thank you for your help.

[Gus]

I would not guess the 100pf is the cause of the noise.  I posted to remove it as step one because you questioned the type you used and there is another low pass filter 1.2K and .033uf.

Step two would follow depending on what happens.

You could have a noisy transistor(s)  I have bought new transistors that were noisy.

Do you have a 100uf or bigger cap as a filter in the power supply as shown in the schematic?

[Nocaster Cat]

I would not guess the 100pf is the cause of the noise.  I posted to remove it as step one because you questioned the type you used and there is another low pass filter 1.2K and .033uf.

Step two would follow depending on what happens.

You could have a noisy transistor(s)  I have bought new transistors that were noisy.

Do you have a 100uf or bigger cap as a filter in the power supply as shown in the schematic?

Forgot to mention I am not using the .033 cap. Disconnected the 100pf with no change and I am using a 100uf filter in the power supply.

[Talon5051]

You could try adding a 10nF cap in parallel with the 1 meg resistor.  I had the same issue with a Tonebender and that was what solved it.

[Nocaster Cat]

So eight hours later I personally think the culprit was the PN2369A. I had a batch of about two dozen and they all yielded the same problem, they were either all bad or they just don't play well with this circuit. As soon as I switched to a different type (in this case my final choice was a NTE123AP), not only did the noise stop but the pedal came alive. Thanks for the help and I'm glad I got it up and running.