Fuzz Face Mods

[Dragonfly]

[ambulancevoice]

image doesnt work man

[yeeshkul]

guys can you please explain to me how the reverse diode in the base works?

[Paul Perry (Frostwave)]

The reverse diode to the base should do two things:
1. lower the bias on the first transistor (I don't know whether this would be significant).
2. give some asymmetric distortion to the signal.

[yeeshkul]

To my inexperienced eyes the diode kills the positive signal swing (is there any bias voltage in between the diode and the input cap?), i am just drawing voltage distributions and stuff and can't find the rason for it . I believe it works, i just don't know why ....

[ambulancevoice]

ok it does now


that diode prevents the saturation of q1

[yeeshkul]

And how does the diode do it?
Also how can get the positive signal swing through the diode?

[Dragonfly]

Joe Davisson came up with that particular diode mod.

Piggybackying... RG (and Brett)

Other ideas from experimentation and various threads.

another good place for the diode is between Q1 emitter and ground....

[joelap]

putting a diode in the way of the signal path like that will block half of the cycle.  Its a similar concept to the way that the octave up on the octavia works, just reversed.

[yeeshkul]

i guess i see now haha, thanks Joe. I've always thought that the first stage of Fuzz Face WAS asymmetric, but this makes sense indeed.

[joelap]

But I'm not saying it wont prevent saturation of the transistor.  I dont know, but it'll still block half the cycle.  It might not make much of an audible difference though.

[ambulancevoice]

But I'm not saying it wont prevent saturation of the transistor.  I dont know, but it'll still block half the cycle.  It might not make much of an audible difference though.

yeah
Joe did say it works for high/med gain silicon transistor fuzz faces
and also, the fuzz face circuit is quite sensitive, so maybe half the cycle is enough to as Joe says "improve the tone"

[Gila_Crisis]

http://www.diystompboxes.com/analogalchemy/emh/emh.html

[unidive]

How would this "tone blend" mod be compared to a simple input cap switch?

because it would be great to have less lows with the option of dailing them in.. but with all the shades of grey instead of just two options

http://i64.photobucket.com/albums/h194/lp59burst/FuzzFace.gif

[mac]

Piggybacking question: instead of the second 2n3904 that has its collector not connected, can a diode be used?

mac

[Dragonfly]

Piggybacking question: instead of the second 2n3904 that has its collector not connected, can a diode be used?

mac

Sure...you'll need to match the diode to the transistor though, otherwise the resulting hfe will be zero. There's a thread on it somewhere....

Seriously though...a 2N3904 is about the same price as a diode... i get them anywhere from $.04 - $.07 each typically....and they are MUCH easier to use in this circuit configuration....

[mac]

Sure...you'll need to match the diode to the transistor though, otherwise the resulting hfe will be zero. There's a thread on it somewhere....

doh! i was thinking about a ge diode...

mac

[StickMan]

The BJT's are enhancement mode, right?

But the input isn't biased at all, so how does the diode interact with it?