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fuzzface oscillation

9/23/2004 2:40 AM
fuzzface oscillation
I built the Fzzface with the selected transistors from Small Bear and it sounds great! Much better than the reissue Arbiter pedal I've also got.  
The problem comes on when I turn the volume all the way down on my guitar (well, actually guitars, they all do it).  
With the volume down to '0' the FF just oscillates a single blah note. Of course, if I switch the foot switch to bypass it stops.  
I tried a 1M resistor to ground on the input side of the first cap with no luck.  
Can someone please tell me what this is about?  
10/15/2004 5:22 PM
Interesting. Most FFs pick up radio stations when you turn down the volume (if you don't use shielded coax on the inputs or a ferrite bead around the input wire). Is your Fuzz control cranked all the way up? Back it down just a notch. I usually find that a small resistor in series with that capacitor to ground (anywhere from 100 to 330 Ohms) eliminates the oscillation from a cranked Fuzz control.  
Also look for paths where the input comes in close contact with the output. You'll find that if you twist the input and output wires together, you can use your guitar volume knob like a theramin! So definitely keep the ins and outs as far apart as possible, both in terms of wiring and in the components of the circuit itself.  
To be thorough, you should also measure the voltage of the second transistor's collector (the transistor lead that gets power from the battery via an 8.2k resistor in the classic configuration). The voltage between that lead and ground should be as close to 4.5 as possible for optimum tone. What I do is use a 100k trim pot instead of a 33k resistor on the collector of Q1 to dial in the correct voltage on Q2's collector. Yes, the two transistors in this circuit are highly interactive, so changing the one changes the other.  
Cool name.  
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