Red Fuzz question

[Lupo]

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

[spongebob]

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?

[Lupo]

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

[Peter Snowberg]

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

[spongebob]

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.

[jrc4558]

Hey, try an inverting buffer on the output instead. Phase cancellation may effectively kill the feedback.