Diagnosing an old dragonfly fuzz board

[bassybeats]

Hi Guys,

Hoping someone might be able to help me. I have finally got round to building the Germocide fuzz, the Dragonfly pedal that you can use up some old low HFE germaniums. Now I have got it going, but I can't seem to get q4/q5 to -4.5v if it set the trim pot to all the way clockwise it gets -2.7v max. Is there a resistor I can change to give me more adjustment? Also the Gain pot seems to be acting funny, at 0 there is nothing, at 12 o'clock there is fuzz and at full there is nothing.

Any advice would be awesome, the thread over at tagboard is mostly dead. Schems attached.

Cheers

[WormBoy]

Seems to be a tonebender MkII, with the Ge's in Darlington mode and a silicon tranny as first stage. For the biassing issue, you probably need a larger trim pot (or a resistor in series with that pot). For the volume issue, something might be shutting down when input volume is too high. If you compare it to a silicon tonebender (like the Tonebender project of Madbean), you'll see they have an extra resistor at the input of Q1 to ground, which is missing in your schematic. That might the cause for the shutting down an maximum gain, but somebody more knowledgeable on tranny biassing might be able to confirm.

PS If you get it biassed properly, I would like to hear your experience with the sound of this thing. I have a number of very-low-gain Ge's lying around that need an application 

[bassybeats]

@wormboy, so finally got it sorted. Thanks for the tips.

Put a bigger 50k trimmer in it and it biased right up, the strange gain issue was a dead 470k resistor ( old stock I had around ).

Tell ya what, this thing has HEAPs of gain, cleans up really well on the guitar vol too. All the Ge's are MP49B russians at ~40hfe and low leakage. Now I have to make one for dad haha

[WormBoy]

Glad to hear you got it up and running. Nice testing rig, by the way (love those clips).

It should have heaps of gain with the first stage boost and two Darlington's (even with low HFE Ge's this should still produce massive gain). I have some even lower AC128's lying around, so this is something I'll breadboard when I can find some time  .