Fuzz Face Q1 Gain

[Aleph Null]

The sweet spot for transistor gain is pretty well established for the Fuzz Face circuit and part of the problem with silicon versions of the circuit is that it's difficult to find transistors in that 80-100 or so hfe range.

Shouldn't it be possible to adjust the gain of Q1 with a potentiometer in series with the emitter and ground? Every version of this circuit I've seen just ties the Q1 emitter straight to ground. It seems like being able to adjust the gain with a pot would make it much easier to dial in a good sound without need to test a whole bin of transistors.

Is there something in the circuit that wouldn't allow for this? Is there some negative side effect I'm not thinking of? I'd love to hear everyone's thoughts.

[skypn]

I don't see how it wouldn't work. I currently (pun intended) connect E of Q1 to 330ohm, then to ground. Everything sounds good to me. 

[WormBoy]

The sweet spot for transistor gain is pretty well established for the Fuzz Face circuit and part of the problem with silicon versions of the circuit is that it's difficult to find transistors in that 80-100 or so hfe range.

Well ... if something gets repeated on the internet over and over, that does not make it 'true' ... it does make transistors in a certain gain range difficult to find and expensive . I have been playing with some left-over transistors with very low gain on a breadboard FF, and can get some nice sounds out of them. Some people have reported good sounds with high-gain silicons, you may have to tweak some values. So, if you have a set of transistors that are higher or lower gain than traditional wisdom prescribes, I would simply try them and see if you like the sound.

There's also the option to combine two high-gain transistors to form one low-gain one ... I will try to look that up. And, there are silicons that have low to very low HFE. They are just a bit more difficult to find.

Edit: it is called "piggybacking transistors"; with google you'll see more about it.

Shouldn't it be possible to adjust the gain of Q1 with a potentiometer in series with the emitter and ground? Every version of this circuit I've seen just ties the Q1 emitter straight to ground. It seems like being able to adjust the gain with a pot would make it much easier to dial in a good sound without need to test a whole bin of transistors.

Surely that is possible. The Aion Solaris FF has a trim pot there for people to play with. I tried it on my breadboard version, and did not particularly like the result with the transistors I tried, but YMMV.

[Aleph Null]

The sweet spot for transistor gain is pretty well established for the Fuzz Face circuit and part of the problem with silicon versions of the circuit is that it's difficult to find transistors in that 80-100 or so hfe range.

Well ... if something gets repeated on the internet over and over, that does not make it 'true' ... it does make transistors in a certain gain range difficult to find and expensive . I have been playing with some left-over transistors with very low gain on a breadboard FF, and can get some nice sounds out of them. Some people have reported good sounds with high-gain silicons, you may have to tweak some values. So, if you have a set of transistors that are higher or lower gain than traditional wisdom prescribes, I would simply try them and see if you like the sound.

This is one of the few times the accepted wisdom seems to be true, at least where my taste is concerned. I've been happiest with fuzz faces when the transistor set fall in that range.

Having looked further into this since my initial post, I've found that a common solution is to leave Q1 source tied to ground and use potentiometers (Maybe 10k?) in place of the two drain resistors, then adjust to get the desired voltages at the drain (0.7v and 4.5v, respectively). This changes the bias of the transistors changing the effective gain. I'm not sure this would let you use any old transistor, but it seems like it would open up a lot of options.