new idea...

[Dragonfly]

as i unpack my stuff in austin, i had a little idea for a fuzz....so, here it is...is you see any possible improvements, changes, etc, post ideas and we'll look at 'em !  nothing too fancy...essentialy a boosted hybrid FF, with some mods...but it should sound good...

get yer breadboards out !

AC


ps...i also included a possible mod on the schemo...its just an idea...it might be interesting to try putting a diode pair to ground just before signal hits the "boost" stage...i'd assume you'd need a cap right after the diodes, maybe a .1uF or so...that way when you boost the fuzz, you also add more nastiness and "grit"

[billings]

Do depletion-mode JFET amplifiers invert the signal?

[davebungo]

So how does the boost control work then?  As I see it, it won't do an awful lot the way it is wired.  Also, what is the rationale behind the circuit.  I mean can you describe what you have added and how it works generally?

[puretube]

Q3 to me looks like trying to compress/negfeedback the input,
although a little too hard!

Gate miswired?

or what do I miss here...

[Dragonfly]

...now that i look at it, *this* may be a better way to wire the boost/sustain section....

the fet booster is VERY similar to Tim's Duende....

[amz-fx]

You may have to move the 0.1uF output cap to the collector of Q2 to get more output, especially if you rectify it.

regards, Jack

[petemoore]

  I'm trying to sort it out...
  It looks like the Mosfet adds positive feedback?
  FF is inverting, Jfet takes the FF output and inverts it, feeding it to the FF input?

[puretube]

FF inverting?

[calpolyengineer]

Mosfet?

[R.G.]

Guys - the FF portion is noninverting overall, and the JFET inverts. The JFET adds negative feedback, reduces gain.

I'm not sure that's what was intended in the original idea. The "boost" pot reduces the total loop gain from input to output as it's turned up.There is also the chance for very high frequency oscillation because of the gain in the feedback path if you're not careful.

If what was intended was a distortion/compressor in one, yes, Jack's comment about needing to rectify before the JFET's gate is appropriate.

If you change the FET path to noninverting, you can get positive feedback OK, but you need to work at keeping it from just being screaming oscillation and no signal.

Ton was more gentle about saying this than I was, but it got missed, I think.

[puretube]

first timeI saw that circuit,
I thought the FET was drawn falsely, ("in-" & "out-put" mixed up),
because I thought the idea behind the circuit would have been:
blend from FUZZ (upper circuit) to BOOST (lower circuit)
by means of the 100k pot...

[R.G.]

Could well be.

I guess that means that neither of us really knows what the idea's object was.

[petemoore]

  I actually skimmed over and read parts of the Tech of FF...figured you guys would clue me in  ...you'd think I'd know this by now...and I should have just placed 'fet' too...[instead of 'Mosfet'][ I sworn I went back and changed that to 'Jfet'...ah well..
  @@ny rate, we're getting closer to understanding what the intented function of the schematic is, and what it does.

[billings]

I think the other way of wiring the boost pot worked better;  with the old way you could get a zero (or practically so) input to the boost section, but with the new one you can only get down to 5/6 of the output signal.

Replacing the booster section with another (non fuzzy) voltage feedback amplifier would get a non-inverting signal, but you'd have to address the low input impedance somehow.  I don't know how that ckt sounds as a booster, though.

[billings]

I'm completely wrong about the first pot arrangement. 

Why not tap the output straight to a 1M pot to ground, wiper to gate?  Replace the volume pot with a 1M as well and it should behave like a 500k on a plain FF ckt.