Fuzz Face Help- New Guy

[Thepilot]

Hello all,

I've got a breadboarded fuzz-face working...sorta.  I used the negative ggg schematic.  I got the transistor pair from smallbear and used his resistor values.  I get the bias of Q2 collector right at 4.5 volts.

The problem is that he specified R6 (the sustain pot) as 120k- this seems extremely high to me.  I currently have a 10k in there with a 470 ohm resistor from input to wiper, and another from wiper to ground- which i think gets me close to a 1k pot.  With that setup all the way up the fuzz is splatty- an undesireable tone for sure.

So- is 120k a reasonable value in any way?  also- i only have 100k pots- can i approximate 120k thanks for the help!- and for the inspiration guys- i love this stuff.

[tcobretti]

I recommend that you provide a link to the schem in question to make it easier for us to answer your question.

R6 says 1k on this schem.  On every FF I have seen, that pot is 1k or 2k.

[hellwood]

post your voltages at Q1 and Q2. also, until you get that 1k pot, 4.5 volts at Q2 doesnt mean anything

[tcobretti]

I am not one of the smarter guys here, but I think that cap is actually oriented correctly.  Note that this pedal is weird because it is Negative ground, but that the +9v is connected to the emitters of the transistors instead of the collectors.

BTW, these PNP Neg gnd FF circuits are notorious for oscillation problems.

[Thepilot]

thanks- that cap is oriented correctly- if you flip it no signal passes.

this thing sounds about like i think it should with the gain knob completely zeroed- problem is that the gain knob is full on- there's a grittiness that fades away.  sorry to suck so bad at describing the problems.  the collector of q2 is at 4.478 volts right now.

[hellwood]

sorry about that cap comment. i saw PNP and assumed it was pos. ground. get that 1k fuzz pot happening before you worry about Q2 Vc

[tcobretti]

I have not had the exact problem you describe, but there are approximately one million threads about FFs, many of which are about biasing them.  I'd search for topics about the Neg gnd PNP FF to see if anyone has had the same problems.

I would first try it as a Pos gnd to see if it fixes the problem.

[darron]

BTW, these PNP Neg gnd FF circuits are notorious for oscillation problems.

putting a 1000uf or 2200uf capacitor across the power rails gets rid of that 'motorboating' oscillation effect. keep it as close to the circuit as possible for best effect. do you suppose that the circuit should have some sort of power protection after that though? i never put it in to preserve that 'true' original ff tone

[petemoore]

  Shown is the GGG NEg. Gnd. PNP FF schematic, quite likely that's the problem...ar least for discussion purposes, it can pretty easily be fixed'.
  I'd build a fuzz face instead, then see if you can get lucky with a NG, PNP circuit, which has an impressive history as problem causer, especially for new guys.

[rubix cube]

You may need to check that the part numbers in your schematic correspond to the part numbers that are specified for resistor values that you got with your transistors. None of the resistor values that get sent with your transistor pair are for potentiometers I don't think- it's the fixed resistors that you get sent values for. Check out the project schematic at small bear and make sure that the R6 on the schematic you're reading is in the same place as the R6 in the small bear schematic (if I remember rightly, it isn't).

[Thepilot]

Thanks gentlemen- i will check all that this afternoon.

It says that the ggg circuit uses the same resistor designators that smallbear sends with his transistors.  I'll take a look at his schematic tonight and see if it works any better.

[rubix cube]

I've just looked and it would appear that R2 in the ggg schematic is R3 in the small bear project. R4 and R5 are correct but R3 in the ggg schematic is called R6 in the small bear project. So your 120K is actually R3 on your schematic (instead of the stock 100K).