si/ge hybrid fuzzface bias and input impedance questions

[unidive]

So as far as I've figured out from reading posts about the fuzzface it is best to have an adjustable bias pot on q2, my byoc kit came with a 10k, which I was then suggested to change to a 25k (Which is now on order) and I thought I was finished

Then I read about the fuzzfoot, and came to really like the idea of a stable potentially higher-than-ge gain silicon tran in Q1 as Q1 as far as I know is only the voltage amplifier that slams the crud out of q2 making the distortion and that it was q2 were the germ sound came from... why then would I have a finnicky device in q1 if it wasn't needed?

So anyway, since they're two different types of transistors with different gains, would I need to have a bias pot for each one to knock either one down to the proper voltage? and what values would I need? I have a 10k and a 25k lin taper pot... the 25k from my reading seems like a good value for ge q2 as I've said, but what value of pot would be best for si Q1's bias? Q1 looks like its biased by a 33k, so I'm guessing 50k

q1 is a bc108, Q2 is a ac127

  and lastly.. what value of pot should I put on the front end of the pedal to up the input imp, I've got tons of different pickups so it'll need to be external.

so far I'll have knobs for impt imped, q1 bias, q2 bias, fuzz, volume, contour and bass contour... this is going to be a busy build , thanks in advance

[joegagan]

for pregain i like a 250k in front of a fuzz face hybrid si (Q1) ge (Q2).
today i used a 100k only because i found a cermet or plastic conductor type pot at my surplus place.

i never found the need to mess with the biasing of Q1, except once in a while i would put a 500 ohm trimpot from Q1 emitter to ground ( another Gus Smalley trick),. Gus says that 100 or 200 ohm to ground improves the 'cleanup' from the guitar volume control, which holds true in my experiencel.

usually the 33k collector R and emitter to ground sounds great to me anyway

[unidive]

I'm not sure what kind of gain the bc108 will have.. but if it happens to be like.. 200 or something, is that going to erase the possibility of having a "classic" fuzzface sound

my understanding is, q1 = 120 q2= 90ish and thats the fuzzface sound, at least from a gain matching prespective

so if my bc108 has a gain of like 220-500 like the datasheet says, isn't q2 going to be massively overloaded? I'd like the option over overloading q2 of course, but I'd like to be able to tame q1 to "classic" perimeters, would turning down the "fuzz" (increasing diminutive feedback if I understand right) have this taming effect? OR, since I'm going to have a socketed transistor switcher (so I can fiddle betwixt two q1's... what low gain silicon could I have available for q1 in addition to mr.high gain ?

[Dragonfly]

I'm not sure what kind of gain the bc108 will have.. but if it happens to be like.. 200 or something, is that going to erase the possibility of having a "classic" fuzzface sound

it will be a classic "silicon fuzz face" sound

my understanding is, q1 = 120 q2= 90ish and thats the fuzzface sound, at least from a gain matching prespective

those gain ranges are geared to germanium transistors, not silicons...though low gain silicons can sound good too...

so if my bc108 has a gain of like 220-500 like the datasheet says, isn't q2 going to be massively overloaded? I'd like the option over overloading q2 of course, but I'd like to be able to tame q1 to "classic" perimeters, would turning down the "fuzz" (increasing diminutive feedback if I understand right) have this taming effect? OR, since I'm going to have a socketed transistor switcher (so I can fiddle betwixt two q1's... what low gain silicon could I have available for q1 in addition to mr.high gain ?

you'll be fine...build it on a breadboard, see how you like it...if you arent happen THEN start tweaking.

the FF is a great circuit...there are so many ways to make that simple circuit sound....

[unidive]

low gain silicon ; do you have model numbers? because if I could find some silicon devices under a gain of 160 that would be just what I am looking for

[Dragonfly]

low gain silicon ; do you have model numbers? because if I could find some silicon devices under a gain of 160 that would be just what I am looking for

2n3903 is good. cheap, sound good, usually 80-120hfe, though some get up to 150

some people like 2n2369 as well...but i find them a bit noisy.

[unidive]

Something kind of related..

but do we really have to get transistors with X amount of gain? like say I had two ac128's, and both had gains of 120 when tested, could I not somehow knock the gain of the ac I'm using in q1 down to say, 80, by tweaking the resistors that set the bias?

I ask this because some smug electrical nerd said sorting trannies by gain was stupid unless you were matching them, and I just told him I'm not sure if that's true, but that's a fairly arrogant thing to say without seeing the circuit