Octave/supersaturation on Fuzz Face circuit

[joelap]

Hey, interestingly enough, with a 25k or 50k trimpot on the output of the diodes, even with the "volume" all the way up, no matter how hard I slam the strings, the sound doesnt drop out.  However, the same effect does not occur with a small value resistor in series with the diodes to the cap... so, problem solved!   Great sound! 

I took voltage readings, and I remember reading that -4.5V is ideal on the collector of Q2 for the fuzz face.  However, mine reads at -6.5/-7V.  If I adjust thge 8.2k resistor down to get Q2's collector to -4.5V, the volume is less than when bypassed, even with the volume on full.  Leaky transistor, or poor HFE a possible cause?  This one on breadboard has noticeably less fuzz/volume to the sound than the last one I built for my instructor... same AC128's I bought off the same seller from Germany... assuming poor HFE or leaky transistor.  Correct?

Joe

[tcobretti]

I'm not an one of the smarter guys here, but the 8k2 resistor is between Q2s collect and the output cap, so as it's value goes up, the circuits output has to overcome more resistance before it exits the pedal.  However, HFEs could certainly play a factor.  And if the leakage is too bad there will be noticeably more hiss than with a low leakage Q.

There are a lot of different ways to build a FF, some of which might make your life easier.  Roger Mayer uses a fixed value (I can't remember what) on the collector of Q2 but a trimpot (50k I think) on the collector of Q1 which allows him to bias the circuit quickly and easily.  Some people advocate the opposite, using a fixed value on Q1 and then a trimpot on Q2.  You might want to try both.

[joelap]

yeah.. I was afraid of that.  trimpots and I aren't on good terms... matter of fact, trimpots and I have had an age-old rivalry.    I really dont like using trimpots, because I find on pedals i used a trimpot to bias something, it drifts over time.  Whereas if I test the circuit and pick the optimal resistor for that specific Q, it stays sounding great.

I'll continue putsing around with the circuit, and report back.