gain for transistors in silicon fuzz face

[fuzz_fanatic]

so i made a fuzz face with germanium transistors and i'm really happy with it and i wanted to make one with silicon transistors using bc108 or something similar. i have two pairs one is 200 & 500 and the other one is 350 & 500. i thought that at least one of them would work fine but the fact is that they both sound like the transistor is not well biased because i can hear what is called gaiting & even when the fuzz sound is good i can still hear it. i am using a 50k pot. where the 8.2k resistor for biasing. what gains should i use?

thanks!

[petemoore]

Same ballpark as the Ge''s, probably biased differently.
 Axis Face, Fuzz Central, socket Q1, Q2 and input cap, use the trimpot to rebias after Q swaps, I'm using 2n2369 for Q1, they're lower gain transistors.
 2n2222a and 2n4401's can be good, mostly it's the gain that makes a difference with NPN si's, BCxxx's being somewhat of a standout [different-er] soundwise than most other types.

[fuzz_fanatic]

are there any bc108 transistors with gains that low?

[octafish]

use any old silis and bias using trimpots. Or build phillip's Axis face with the specified trannies for a quasi germ FF.

[brett]

Hi.  You might try a power transistor, such as a BD139 (hFE of 100 to 150) for Q1 and/or Q2.  Or Phillip's famous 2N2369A (hFE about 70).  Unfortunately, you'll find it difficult to get good tone with hFE over 200 in Q1 (though from memory it will work if you put a 220 ohm resistor between the emitter and ground).
 
Use that pot to bias the collector of Q2 to between 4 and 5 volts.  Unless there's a bad connection somewhere, the bias is then ok.

Good luck

[fuzz_fanatic]

the thing is that i get a good tone but with that there these low buzz when i hit the strings like when you have gating and it is always there no matter how i set the 50k pot i have (where the 8.2k resistor was). so i guess i'll try other gains...

[Sam]

are there any bc108 transistors with gains that low?

I measured a few BC108. Can't remember the exact Hfe - but they sound really good in a Si FF. I tried several combinations Hfe wise but I thought the best tones came from both being BC108. There was some oscillation at full volume but I cured it with a small cap between both collectors (as in the Sili-Face).

[petemoore]

You could piggy back the transistors and set the gain with the emitter to emitter resistor...
 I would just stick sockets in a test/swap/test, get some different gain tranny's and try again.
 Joe Davisson shows the "Antique Face', with a compression diode and it calls for higher gain Q's 2n5088 [IIRC]...maybe take a look at that and see what you think, I built it, and it is smoothe and compressed more than my FF's too !!

[mojotron]

are there any bc108 transistors with gains that low?

I measured a few BC108. Can't remember the exact Hfe - but they sound really good in a Si FF. I tried several combinations Hfe wise but I thought the best tones came from both being BC108. There was some oscillation at full volume but I cured it with a small cap between both collectors (as in the Sili-Face).

That's been my experience as well, I have used a few BC108, BC108C and BC109 transistors in the FF circuits and these are wonderful transistors. I did some unguided unscientific transistor swapping with the 10 or so BC10X transistors I have to get the best sound - the BC108 sounded the best - any of these pairs sounded great once I got the higher gain transistor into Q2 and biased it by ear with the collector trimpot. I have to say, I never got the "best" sound when biased at 4.5VDC at the Q2 collector.

What I use when I build stuff for others is a PN2369A in Q1 and 2N5088 in Q2 and bias by ear. This combo is a very close 2nd to 2 BC108s, and have gotten it to work so often that I don't even sort PN2369A and 2N5088s for the FF circuit use anymore - unless there is a specific request. I also specifically recomend BC549 and AC127 transistors as a great combo, or used with either the PN2369A in Q1 or 2N5088 in Q2 - there is always room for improvement, AND this is just going by what my ears are hearing - YMMV.