bias control on a fuzz face

[carboncomp]

What is the best size for a bias control on a fuzz face, and is it worth putting a small fixed value before so there is always a little resistance? 

[Jaicen_solo]

Go Here:
http://www.geofex.com/article_folders/fuzzface/fffram.htm

The bias control you're using is really dependant on which transistors you're looking at using.
If you're using modern Silicon transistors, you can more or less get away with a fixed bias.
If you have leaky Ge transistors, you're going to need a wide range Bias control to get in the sweet spot, depending on the leakage figures.

[LucifersTrip]

What is the best size for a bias control on a fuzz face,

you don't want to stray too far from the 8.2K resistance so I wouldn't use higher than a 10K or 20K pot. I choose transistors so that I only stray +/- 3K from the 8.2K to get 4.5v (ie, ~ 5K - 11K)

If you have to go too high (or too low) to achieve 4.5v on Q2's collector, the sound will most likely not be great...

and is it worth putting a small fixed value before so there is always a little resistance? 

yes, because the sound you will get with 0K will be pretty bad...a boomy mess

[carboncomp]

Im having to use a 47K to get below 6 with a whole bag of geraniums ranging from 110-160   the sounds nice fuzz.....but sounds like 47K is fundamentally to high?

[joegagan]

is your 1k pot and the cap to ground correct? sounds like something is goin on there.

is your feedback resistor wired correctly?

are your other power resistors measuring correct?

[carboncomp]

here are the other voltages

Q1
E 0
B 0.06
C 0.11
Q2
E 0.07
B 0.11
C 8.9 (8k2) 5.6 (47k)

the 33k, 470R and 100k all measure right on the multi meter (PCB and pots all Grounded to enclosure).

[LucifersTrip]

The voltages on both are far enough off from what they should be that a mis-wiring/bad connection is a high probability.

If you picture a clear closeup of your circuit maybe someone can spot an error.

btw, what transistors did you use? did you measure leakages?  if pnp, the voltages should be -

[carboncomp]

btw, what transistors did you use? did you measure leakages?  if pnp, the voltages should be -

Should be - ?  you ling me hanging here!

I bread-boarded up to make sure I got the circuit right, and with BC108Cs I get 5-6V no problem with 8K2.........BUT!!!

Then I flip the caps and polarity to test my PNPs out (using the modern NKT275 and a couple of Newmarket NKT275 from a salvage), and on them I get -8-9v on the Q2C regardless of combination, and im trying about a dozen sets here?

not measured the leakage, will have to borrow a friends peak tomorrow if he lets me!

And one more question, is the voltage on the Q2C supposed to change when playing though it, and if so do I measure voltage playing or at rest? 

[LucifersTrip]

btw, what transistors did you use? did you measure leakages?  if pnp, the voltages should be -

Should be - ?  you ling me hanging here!

yes, if neg ground, then you will measure +. if pos ground (pnp), the voltages you measure will be -. remember, black lead on ground & red lead on the point you are measuring.

I bread-boarded up to make sure I got the circuit right, and with BC108Cs I get 5-6V no problem with 8K2.........BUT!!!

Then I flip the caps and polarity to test my PNPs out (using the modern NKT275 and a couple of Newmarket NKT275 from a salvage), and on them I get -8-9v on the Q2C regardless of combination, and im trying about a dozen sets here?

did you measure gains at least? .... ~ 60-90 for Q1 and 90-120 for Q2.   it won't matter too much to the voltage, but did you change the 330 to 470? that will lower it a little

not measured the leakage, will have to borrow a friends peak tomorrow if he lets me!

And one more question, is the voltage on the Q2C supposed to change when playing though it, and if so do I measure voltage playing or at rest? 

yes, it changes when you play...leave the dmm connected and you shall see...measure at rest.