FET/Si fuzz face

[mac]

This is a draft of a fuzz face with a fet at the input.

Unlike a bjt, a fet needs the source voltage to be over the gate voltage, so grounding the source may not work since the gate is at half a volt or more typically.
I first used a resistor at the source bypassed by a big cap to set the source over the gate. Then a couple of diodes as Jay Doyle suggested.

Since the gate is almost an infinity resistor, gate voltage Vg is equal to the emiter voltage Ve, Vg=Ve, and so the drain is a diode drop away from the gate, Vd-Vg=Vbe. Since ie is almost equal to ic then, Vg=4.5v*1k/Rc.
Once the collector voltage is set by Rc, the fet voltages are the same, no matter if there are a couple of diodes or a resistor at the source.

Another cool result is that the feedback resistor does not alter the bias. I used it as a drive control.



The big difference with the std fuzz face is the input impedance. It sounds brighter, like Aron's Rocket. Guitar volume works fine.

Thanks to Jay Doyke for his ideas.

Ideas are welcome.

mac

[Dragonfly]

Nice work  !

Also, check out http://www.geocities.com/tpe123/folkurban/fuzz/fuzzyfaces.html for mosfet / fet / bjt variations of the fuzz face !

[mac]

Added to favorites a long time ago...

mac

[mac]

I should try a Ge transistor. And a fet at Q2. Bias may be tricky.

mac

[MartyMart]

Nice, here's one from last year that sounds good:

http://www.aronnelson.com/gallery/v/Martys-layouts-and-photos/FetFuzzV1_0.jpg.html

http://www.aronnelson.com/gallery/v/Martys-layouts-and-photos/FetFuzz.mp3.html


Marty.

[earthtonesaudio]

How about changing the "drive" pot to the one suggested in the "many faces of fuzz" here (top left)



Don't know if it would work with the jfet, but it might be cool.

[mac]

I thought about that, but I had to add a big cap and wanted to keep things simple.
Reducing the feedback resistor not only increases the negative signal going to the gate, but also lowers the gain of the fet because the pot is the gate resistor.

mac