The temperature in the Rock Room this time of year is probably 8-12 degrees (American) cooler than the rest of the house, even less if it's frosty out. That's cold enough for the germanium bits in my Fuzz Face to cut off sustaining chords and gate out everything except the attack on single notes. I can get the roar and sustain back by setting the Fuzz Face on top of my electric radiator for a while, but afterwards as the pedal gets cooler it starts to fizzle out again.
I like everything about the pedal in the summertime and early fall, and I understand that this sort of behavior comes as a package deal along with the magic of germanium fuzz -- but I thought I'd see what I could do to get it through the winter.
The internets talk about heat/cold effecting the bias voltage of the germanium transistors, especially the second one in the signal chain. Here's a schematic of a 4-knob pedal similar, but not completely identical, to the one MadeByMike MadeForMe. I didn't check component values except for the one resistor I thought I needed to deal with. So any deep secrets of the pedal's true design shall remain known only to its creator.
Anyway, the trouble happens at the top (collector) of Q2.
I read that people like to get (negative) 4.5 to 5 volts at the collector of Q2. Mine was measuring less than 2 volts at basement temperature. These germanium transistors are interesting: the heat from touching one with a fingertip caused its collector voltage to creep in one direction, and after removing the finger it crept back in the other direction.
To try getting more volts to Q2, I clipped a spare 100K pot in parallel with the resistor right above Q2. That gave me slightly less than the stock resistance, and as I dialed the pot downwards the Q2 voltage went up. At a little over 4.5 volts I hooked up a guitar, and the Fuzz Face was back to its summertime self again. With this particular pedal, I could get good sounds at lower voltages too, so I guess that's not some magic number.
I think I'll keep that control handy on the front of the pedal for now, but I don't want to disrupt a nicely-built device too much. So I sort of borrowed the existing 50K control from the input, rerouting its wires to place it in parallel with the resistor above Q2 where my 100K test pot had been. BTW thanks for the sockets, Mike! The transistors stayed safe from solder heat.
I understand that the Analogman Sun Face and other boxes offer a similar Q2 bias control, but I haven't seen a diagram of exactly what they do. I added a 2.2K resistor to bring the overall max resistance of the whole arrangement up a little higher than the original, with a minimum of 2.2K. I figure that will give me some room to compensate for both cold and warm temps, and I can still hit the original setting too.
I'm happy with the cold-weather results so far -- the mod works well alongside the Contour control, and I can get a lot of variety. I do miss the fine control of the input pot, though I can at least get a similar effect with my guitar's volume knob. I think I'll leave things this way for a while, and decide later whether to add a bias trim-pot and give the 50K knob back to the input as designed.
