Silicon Fuzz Foundry

[mattkwilson]

Hey there!
So I've made a Fuzz Foundry with a 2N3904 as per the design, but have swapped out the 2xAC128's for 2x3906. I had read that this was just a straight swap, but things aren't sounding right. I DO get sound, and very similar sounds to what I think I should be getting. However, I get note cutoff very quickly, especially when playing higher notes - very little sustain at all, even with the Gate pot turned all the way down.

I did some research and found that maybe biasing needs to be reset? From what I understand that would mean adjusting resistors to modify the voltage at the Base of the transistors, right? So basically I'm asking:

1) Anybody done this before and have a similar issue? And if so, how did you fix it?
2) Could the biasing be the issue?
3) Could it be something else entirely?

To help with the diagnosis, I measured voltages on the transistors wrt ground with all pots at 12 o'clock:

Voltage source @8.1V
Q1 (2N3904): C=1.07V, B=0.62V, E=0V
Q2 (2N3906): C=5.07V, B=4.47V, E=2.53V
Q3 (2N3906): C=3.19V, B=2.53V, E=3.18V

I've also switched Q2 and Q3 to see if there was any difference and there's no difference.

Any suggestions appreciated!

 

[Feral Feline]

Bump

I've got nothing to help you, other than bumping the thread.



Aion suggests the Si version sounds/behaves quite differently from the Ge, and also recommends the following starter settings:

Drive: 5
Volume: 3
Comp: 2
Stability: 10
Gate: 0