Is over-biasing a GE Fuzz Face harmful?

[oliphaunt]

I am making a 5 knob Fuzz Face, PNP with some sweet AC128 low leakage transistors.  The controls are Pre-Gain (a pre-input cap volume to simulate the guitar volume knob), Fuzz, Tone, Output Volume, and Bias (Q2).  For the bias I have a range of 1.1 to 7.7 volts.  I really like the bias set about 6.5V with the pre-gain rolled way back for a light OD sound. 

Is there any harm in running the fuzz over biased like that over the life of the pedal?

[Caferacernoc]

I hope not. I like to bias my jfets like that. 5.5 to 6 volts instead of 4.5. More even harmonics and "tubey" sounding.

[earthtonesaudio]

Totally safe.  (hint: recall the emitter follower)

[sshrugg]

My fuzz face has been biased at somewhere around 5.7 volts and it's sounded great for a couple of years : )

[jonfoote]

sorry to stray off topic but i just notice the tone pot on your diagram. never seen one like that.

how well does it work as a tone pot and does it mess with the bias?

ta

[oliphaunt]

Thanks to all above for the responses.

sorry to stray off topic but i just notice the tone pot on your diagram. never seen one like that.

how well does it work as a tone pot and does it mess with the bias?

ta

The tone control works very well, and was the best simple design I could come up with that doesn't effect the tone at all when the pot is off.  I could never get the SWTC to be completely transparent, it always rolled off some highs.  This design works best for me inside the i/o caps where voltage is present.  I had this on the breadboard for a week constantly playing with the bias resistors and pot, and checking them to see how they reacted together.  I never noticed the tone control having any influence on bias, but I admit I wasn't looking for it.  I will be working on a si/ge switchable version maybe later today so I 'll check it out and see if there is any influence.

[fuzzo]

I really like the "smooth" control on fuzz face (better than the "drive knob" for me, it acts like a kind of "fuzz/tone" knob) but I don't wire it like you schematic shows. Just a variable resistor, not connected to the ground.

What does exactly the tone ? that looks like a simple high pass filter.

[oliphaunt]

I really like the "smooth" control on fuzz face (better than the "drive knob" for me, it acts like a kind of "fuzz/tone" knob) but I don't wire it like you schematic shows. Just a variable resistor, not connected to the ground.

I see that the Smooth control in other circuits are wired as you say, a variable resistor.  Mine works the same way, that's just how I did it without looking at other schematics.  I'm not sure if one way is better than the other.  I agree with you the Smooth control is a much better control over the gain than the fuzz control, though sometimes they work together well.

What does exactly the tone ? that looks like a simple high pass filter.

Yes, it is a simple high pass filter.  It just rolls off some of the buzzy high end.  It is super simple, but effective for my purposes.  I like the Fuzz Face with the bias set high and the Smooth control very low for a smoother overdrive sound.  I don't know why but over-biasing lowers the gain, gets rid of some of the fuzzy "sizzle",  and adds a lot of punchy low end.  Rolling off the high end a little bit helps make it even more like an OD and less like a fuzz.

[fuzzo]

and it's really effective ?

I'd like to build a fuzz with simple fuzz face circuit and a tone control to have more tone possibilities . Once I tried putting a high pass filter linked to the output cap and nothing really cool happens, at max the sound wasn't here anymore. Strange.

The textone nutz (austone) has that kind of pot but I don't see how it works, can you explain how that works ?

[oliphaunt]

Yes it's quite effective in this circuit, but there may be a disadvantage.  I have noticed that in some circuits you get a noticable drop in gain as you roll off tone.  For my purposes I like the Fuzz Face to have a low gain setting anyway, so that works well for me, but even so I didn't notice the gain drop being much of an issue in the FF, where it is a big issue in an overdrive where I tried the same trick. 

How does it work?  Well, I am not a real electronics guy, but my basic concept is that the cap allows high frequencies above a certain point to pass though it and be shorted to ground.   Perhaps someone else will offer a real explantion.

I also tried a high pass filter after the output cap and it also had little effect on the FF.  Plus, the ones I have made always seem to have some impact on the tone even when the knob is rolled all the way off.  I guess a larger value pot might eventually make that problem go away, but would also make much of the range of the pot useless.

[fuzzo]

Ok thanks, I'd try that in my next fuzz pedal. That sounds cool .