Silicon F.F. question

[Clubman35]

Just built a silicon fuzz face and have a question.... any ideas why it farts out and gets really noisy when both the volume & fuzz are turned up near max? Gets really thin, and clips the signal. Roll back both controls to about 3/4, and everything sounds good.  I'm using BC108 transistors. Many thanks.

[LucifersTrip]

Just built a silicon fuzz face and have a question.... any ideas why it farts out and gets really noisy when both the volume & fuzz are turned up near max? Gets really thin, and clips the signal. Roll back both controls to about 3/4, and everything sounds good.  I'm using BC108 transistors. Many thanks.

remember, the debugging thread:


but this sounds like you simply don't have Q2 collector voltage at 4.5v.  adjust the 8.2K while one end of your dmm is on ground and the other on Q2 collector

[Clubman35]

Thank you.

I'm sure this has come up before, but to sort through all the results of a search for 'Silicon Fuzz Face' would take a year and a day.

[Renegadrian]

I built some stock and never like them 100%, guess this read is worth! 10 k trimmer and 100 pf  cap to smooth the gain...
You'll turn your FF from ugly to sweet!!!

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

[Clubman35]

Thanks. Good info.... I think I'm going to try a couple of those mods.

[col]

If you have some other transistors of the same type try them. I found individual ones to make a huge difference to the sound. In one I tried BC107, BC108 and BC109 all unlettered plus some B and C suffixed until I found a pair that sounded good. Usually as you say it got farty and gated on full or was missing 'something'. The best sounding one I made for a friend had really low gain (for silicon) transistors NKT10339 of around 60 to 70. The two power transistors in a low energy light bulb are also very good but are usually BCE pinout and look like a BD139 which I have also had success with.
Have a search for Si FFs and low gain transistors as I know other people have found the same thing.

[rockhorst]

Thank you.

I'm sure this has come up before, but to sort through all the results of a search for 'Silicon Fuzz Face' would take a year and a day.

What LucifersTrip meant to say was that when you have an effect that doesn't work, giving some DMM measurements of IC, transistor and diode voltages greatly improves the ability of others to help.

[Renegadrian]

I had some similar problems in the past, oscillation or motorboating with gain or gain and volume maxed.
The sound was OK till 9, but going to 10 was just beyond that limit...So yeah several ways to smooth the excessive gain and the fart can be found in the link I posted above.

[petemoore]

Roll back both controls to about 3/4, and everything sounds good
   Might be this is 'it' then.
    Otherwise 1 complete debug [at least testing all the grounds, V+ etc., measuring, then setting up the circuit bias.
   FF can be setup for VHGain/oscillation/ducking even.
    Reduced PS voltage, offbias circuit conditions, extreme gain, high input levels...
   Super high gain is easy to get set up as well as other wierd behaviours like flatulence, setting it up to get cleaner as the guitar volume is rolled back is another popular FF setup 'trick' to consider.