Help me fine tune my effect

[Herr Masel]

It's the big-daddy again, I've tried it on a fender solid-state amp which is where it sounds best (not bad at all), and two tube amps - a jcm2000 and a jcm800 clone from the sixties. On the clone it sounds abit fuzzy, with some octave and stuff, on the jcm it's a straight up octave fuzz. Why doesn't it like tube amps? Here's the schematic http://www.runoffgroove.com/grace.html. Last time I asked someone said it might be a bias problem, but I don't know what that means or how to fix it. I'll add that I strayed a little from the schem, adding a tone pot, and a 2n5457 instead of the j201.
I know I've asked about this before but I couldn't get any answers. Thanks.

[Herr Masel]

No one knows what I can do? I've searched and searched and nothing comes up on getting rid of the octave sound. I have no idea what is causing it... thanks.

[Joe]

Maybe adjust the 15k resistor so the drain is near 1/2 supply voltage.

[Herr Masel]

Sorry for being difficuilt, but what does this mean? Should the drain be 4.5v? What do you mean by supply voltage.

[Herr Masel]

I've been looking but still not much info on this. The best I could figure out is as follows:
the reading on the drain of the transistor is 3.38v, so I figure I need a bigger resistor there. I tried calculating with ohm's law, so
V=IR
3.38=IR
3.38/15k=I
I=2.25
3.38/2.25=1.5
This is probably wrong, but this is what I could work out, also it wouldn't make sense to change the resistor to 1.5k, or is it representing something else?

Yours,
Clueslessly seeking a clue.

[Herr Masel]

*Chough* *spits blood*

[Steben]

Hi there,

No, a 1k5 resistor won't simply "do" the trick. Replacing the 15k with a 50k or even 10k trimpot could be a solution (to adjust till 4.5V).
Still, with 3.4V, you won't get (noticeable) "octave up" sounds, and definitely not interfere with amp choice. I have no explanation. I find it very hard to think about a reason why it sounds better on your SS amp...
Fuzz faces tend to sound superior with a slightly pushed tube amp - that I know - but an effect that is acceptable on SS and inacceptable on tubes... 

Bias problem means the signal is set at a mean voltage value (bias voltage). biased at 1/2 supply Voltage (like the 4.5V story) brings in the most symmetric possible and highest headroom (largest sweep at both sides). When an amp has no capacitor (allows only AC current = signal) in front of it (most tube amps do not, most SS amps do, you see?...) it isn't protected against DC current (which sets bias) and therefor can be misbiased by the circuit in front.

Now, as I see in the Grace circuit there is a cap in front of the pot, so no DC current there going to the amp. Unless... You connected the pot not to the earth rail, but to power rail. This means there is 9V DC going to the amp or slightly less, according to the input resistor of the amp. This explains the variation on different amps. You should check the DC voltage (no guitar signal) at the output of your effect. If it changes with the volume, you're done for: If so, solutions: put another cap after the pot before the output OR BETTER resolder the pot lug from power this time correctly to ground.

[Herr Masel]

Well I don't know how you came up with that but you are right, almost! I measured from the output jack and it sweeps with the volume pot from 8.5 to 7.7, the battery on itself is a little higher than 8.6. But it is soldered to ground as should be, I didn't make any mistakes there, so I will try the cap, but what value to make it?

[Steben]

Well, a couple of 0.1uf's would do. Try for example a 0.47. tell me how it works ou!
Glad I could help a bit!