I built this fuzz face based on the idea of having 2 piggyback transistors on top of the original 2 transistors.
It also has 2 trimmers to adjust the bias of them.
I built it and it sounds great but it needs more sustain.
My question is how can I bias the transistors to get the best sustain out of it?
I know the bias pot should be around 8.2k but what about those trimmers?
They have micro adjustment so it's a pain trying to figure out the best values.

I had asked myself the same question for years, trying various "special sauce" recipes, including the piggyback transistor trick to reduce gain, until I finally found something that works for my taste and was quite the opposite of what my preconceived notion told me I "should" like: high-gain transistors!

I know that doesn't help with your problem, which is likely due to the finnicky biasing of piggy faces. I don't know any other way of getting the best sound out of those other than fiddling with the bias until it's just right. I am just saying that if you cannot get it to where you want it, you might be better off setting it aside and explore a few other branches of the vast fuzz face family tree.

HTH
Andy

Do I read this correctly.... using low gain techniques and then realising it is lower gain? 

Quote from: Steben on January 08, 2025, 04:19:51 PMDo I read this correctly.... using low gain techniques and then realising it is lower gain? 

In case this needs some explanation for the OP: low gain transistors (or low gain simulation tricks like piggybacking) need to be biased very precisely to get good sustain and even then it is usually not great. High gain transistors provide much more sustain, even when the bias is "wrong".

Andy

p.s.: There's no such thing as "wrong bias" in a fuzz, as long as you like the sound. By "wrong" I meant "not tuned for maximum sustain" in this case.

Apologies if it sounded blunt.
Have you built fuzz faces before with singular low gain transistors that sounded as expected?
(Piggybacking is not the ideal first fuzz face to build)

Try change 1K pot to 2K pot 

If you go with Figure 10 of this application note:

https://pe2bz.philpem.me.uk/Parts-Active/IC-Analog/-%20AN-National/AN-286.pdf

you will see a temperature controller.  Controlled transistor temperatures offer one way to stabilize one major variable.