MOS-Face / Silicon Fuzz Face hybrid: biasing help?

[masinyourface]

A few weeks ago I posted help on a Silicon Fuzz Face I was working on. It turned out great! But now I'm ready to take it a step further! I'm now attempting a MOS-Face / Silicon Fuzz Face hybrid!

After reading Tim Escobedo's "The Many Faces of Fuzz" (http://web.archive.org/web/20050513200126/www.geocities.com/tpe123/folkurban/fuzz/fuzzyfaces.html) I was inspired to attempt to mod my fuzz face with different transistors. Jack Orman's MOS-Face (http://www.muzique.com/schem/fuzzface4.gif) had always been a favorite of mine, so I started with a hybrid circuit of Tim & Jack's MOS-Faces.



R.G. Keen's Technology of the Fuzz Face (http://geofex.com/Article_Folders/fuzzface/fffram.htm) had been instrumental in helping my silicon fuzz  face sound amazing, so I figured I'd try and follow his advice on the transistor selection. He suggests an hfe of 70-100 on Q1 and 100-130 on Q2. The silicon 2N4123 I'm using for Q1 has a gain of 78. The MOSFET I'm using is a 2N7000



With my whole thought process explained, now I'll move on to my actual problem 

I'm having a difficult time biasing Q1. Q2 I'm having no problem getting 4.5 volts on the drain (collector). Q1 however I am only able to get a minimum gain of 1.8V and I'm trying to get it closer to 1.
Here are my exact transistor voltages.

Q1:
C-1.835V
B-0.555V
E-0.000V

Q2:
D-4.500V   (collector on a BJT)
G-1.845V   (base on a BJT)
S-0.555V   (emitter on a BJT)

In attempts to lower the collector voltage of Q1, I've shorted the feedback bias and maxed out the collector bias to 1M. Anybody have a better idea? Any help is much appreciated!!!

[LucifersTrip]

here're si voltages from ggg...you're not far off

Q1 Collector 1.4v
Base 0.6v
Emitter 0.0v

most builders use higher gains for silicon (I believe RG's 70-100 was for ge), though, I prefer lower

the Mos-Face calls for a 108 or 5088/9 which would be in the 300-500 range, probably
http://www.muzique.com/schem/fuzzface4.gif

bottom line...do you like the way it sounds now?

[masinyourface]

Haven't tried a 5088, I tried a 3904 and it was too much for what I'm going for 

The gain is about where I want it with the 4123. I originally chose that transistor for Q1 because it fell into the hfe range I was looking for. After a bit more research I actually found out it's the same one that SBE recommends with their silicon fuzz face. My biggest complaint of the tone is that it has too much low end for my taste. I was planning on trying different input/output caps after I get gain the where I want it. Maybe after that I'll work on a tone stack! I've gotta say, no thanks to the DIY stompbox forum, I've got an incurable addiction now! Haha 

[masinyourface]

One thing I'd like to add for anyone that stumbles across this thread, taking the output straight from the collector/drain of Q2 is a must in my opinion! You're able to get a greater output volume without using higher gain transistors that clip the crap out of the signal. It does have somewhat of an effect on the tone by effecting the frequencies altered by output cap, so be aware that you might need to mess around with different output cap values to find your cup of tea.

[Kesh]

[brain  fart]

[PRR]

> I'm trying to get it closer to 1.

Why?

Look at your voltages. Q1 C is *always* equal to Q2 G plus Q1vbe (and a little drop in Q1's base resistor).

Q2 being a MOSFET, the Vgs is typically a couple volts, not the 0.6V of a BJT.

I'm not sure what's wrong with 1.8V? The distortion mostly happens around Q2 Drain, that's the interesting part. Q1 just tickles Q2. If Q2 needs to be tickled around 1.8V, so be it.

[Kesh]

Surely Q1 C = Q2 G as they're connected by nothing but a wire

[masinyourface]

Yikes! I suppose even the best of us are subject to typos 

Both Q1 C and Q2 G read 1.835V

[PRR]

> Surely Q1 C = Q2 G

I was not even looking at the 0.01V different... insignificant, could be power wobble from one moment to the next.

You can NOT get Q1 C lower and still have Q2 conducting, not with normal MOSFET gate turn-on voltages.

You could try to select a 2N7000 with lower turn-on, but what do you gain? Arbitrary DC voltage, not different signal clipping action.

[Kesh]

PRR, I was responding to your:

>Q1 C is *always* equal to Q2 G plus Q1vbe (and a little drop in Q1's base resistor).

I'd have thought Q1 C is always equal to Q2 G, period.