Axis Face needs more sustain

[Sindran]

I build the silicon Axis Face from fuzzcentral. It sounds good but needs more sustain. When I play long note it dies in very uncool way. It's a bit gatey I would say.
I've been trying to adjust the trimpot, but it doesn't help. The transistors are matched pair for fuzzface from Banzaieffects.com.
They are supposed to be smooth/soft sounding.
Maybe I just need more gain, but when gain-pot is full and "smooth"-control low it starts oscillating.
...So what can be done to the circuit to fix that problem?

Thanks...

[petemoore]

  Is it biased 
  See DEBUGGING and GEO "Technology of the Fuzz Face".
  These pages will help you to provide bias info.
  Your post seems to indicate probable misbias.

[Sindran]

Threre is a 10k trimmer pot on collector of Q2. With that I can adjust the (Q2 collector) voltage to 4.5V.
Is there anything else that needs biasing???

here's the schematic I used:
http://fuzzcentral.tripod.com/axisfacesi.html

[petemoore]

  It should bias up nicely on all transistor pins with 4.5v on the collector...or at least I guess. But if it's gating there may be some other bias issue...pretty hard to say.
  If you want to take bias readings, you can compare them with:
  ROG [or is it Homewrecker], has FF pin voltages for reference...including Si FF's, 
  Or post the readings here for analysis.

[Gyoon]

This is an old thread, but I am having the exact same problem as Sindran.  When you measure collector voltage, you are measuring it against ground, correct?  The 10 bias trimmer does very little, going from 9.06 v to 8.85 v with the collector of Q2 measured against ground. It doesn't sound bad, actually.  Sounds really synthy, which I like on my bass.  Cuts out the low frequencies and gives it an interesting sound. 

[petemoore]

 When you measure collector voltage, you are measuring it against ground, correct?
  Ground is the common reference point by which bias voltages are compared.
  The 10 bias trimmer does very little, going from 9.06 v to 8.85 v with the collector of Q2 measured against ground. It doesn't sound bad, actually.  Sounds really synthy, which I like on my bass.  Cuts out the low frequencies and gives it an interesting sound
  I assume the + reference voltage is a battery of at least 9.06v, and that there may be another wiring issue with this circuit which precludes the 10k biasing it. The collector should move to ~4.5v.
  See the Debugging thread...measure resistances...to debug, the full set of info is needed, battery or supply voltage, all the actives chosen and their pins voltages, schematic, how closely you stuck to it...

[Gyoon]

Found the problem!  I switched the 1k attack pot with the 100k smooth pot.  Works great!  I even like it better than the EPFM tube fuzz!  Really responsive but with more cut and grind.  Makes my p pickup on my bass really come alive.  Thanks, Pete.  I just might post some soundclips when I get the thing housed.

Glenn

[phillip]

Glad to hear that you got the problem sorted out!  The Axis Face should indeed have a long, smooth sustain.  I like to bias the second transistor right at 4.5V, but you can also run it at 5V which makes it just a touch "fatter."

Phillip