Hi there,
I think I'm getting mad! I built Robin Tomtlund's Red Fuzz (see ggg) on a perfboard for the third time and still it doesn't work properly. I used a LF351 on one and a TL071 on another. JFET is BF245 because I couldn't find a J201. The problem: I get squealing when I'm turning drive and tone up. When playing with the tone pot the squealing sound is pitched up and down. It's getting worse when I'm using a singecoil. When the tone and drive pots aren't turned up too much, the pedal sounds just like it's supposed to. I like the sound of the Red Fuzz so much that I won't give up. Can anyone help me? What could it be?
Lupo
What you describe sounds very much like oscillation, is your circuit battery powered? Then try putting a 100 uF cap between the supply rails, that might help stabilizing it...
Did you compare your voltages to those shown on the GGG page (http://www.generalguitargadgets.com/v2/diagrams/redfzzad.gif)?
Thanks for your answer. Yes, it's battery powered. The 100uF cap didn't make a difference.
I measured the voltages:
opamp
-input: 4.7v
+input: 3.8v
output: 4.7v
JFET
G: 0v
S: 2.1v
D: 9,3v
Slightly different from those shown on ggg. Could the reason be my s**tty voltmeter or the different jfet?
Another thing I have to mention is, that my pedal looks like a rat's nest and I don't use shielded wires. I just thought the symptom would be different if it was a wiring-problem (remember? tone control pitches the squealing sound up and down). But I don't have any skills in electronics. I just know that you mustn't connect the guitar directly to a wallsocket :)
In addition to that 100uF, try adding a 0.1uF across it and maybe a 0.01 or 0.001 too.
I hope that does something.
Good luck,
-Peter
Hm, voltages are fine, when I built the circuit myself the readings were also a little bit off (I used a TL071 + J201)
It shouldn't make a difference which JFET you use, I think its purpose here is to serve as an output buffer, you could omit C6, R6, Q1 and R7 for debugging purpose and it should still work.
Hey, try an inverting buffer on the output instead. Phase cancellation may effectively kill the feedback.