Incorporating a high-pass in a Fuzz Face?

[ribolovec2]

Hi, I've been thinking recently about building a Fuzz Face clone, but i want to make it a bit more versatile than it is.. i wanna experiment a little by adding 'switchable' mods. One thing I've noticed about the Fuzz Face is that all frequency get the same amount of clipping/fuzz. I think that at times this may sound a bit unpleasant (i know that is a typical characteristic of the fuzz face, don't want to hurt anybody's feelings here). Is there a way to implement something similar to a tube screamer - below a certain corner frequency gain gradually decreases to 1 @ DC (i mean the 'drive/fuzz'-gain, not overall gain - that would be simply a tone control). Could you please help a little? Here's the schematic:
Thanks in advance, guys!

[Mark Hammer]

One of the simple-but-elegant innovations that Joe Gagan introduced so many of us here to, within the general Fuzz Face topography, was a variable bass on the input.

Theformat is fairly simple.  Replace the existng input cap (2u2 in the example shown) with a much smaller one, perhaps 1/10 the original value (or less), and place the larger original value, and a variable series resistance (like a 100k pot), in parallel with it.  When the resistance is high, the signal enters primarily through the smaller-valeu cap.  As the resistance is decreased, the larger-value cap becomes a more viable pathway for those electrons, and more low-frequency content is introduced.  When the pot resistance is zero, the two caps are effectively combined.

Works like a charm.

[joegagan]

the input cap sweep pot works,  except loses balls when the thinner caps are in circuit. some people may find it acceptable, but really, it tunrs into more a of a mild fuzz/ OD unless something is done to recapture some gain.  hence the third gain stage of my subsequent designs.

another solution is to tap off a hotter output of the FF by splitting up the biasing R of Q2 and using switching or other means to take a hotter signal closer to the collector of Q2 when the treblier side is engaged. look at the tone control out blend of a tonebender mk3 ( keep in mind that Q2 is Q3 in this case) for one way of doing this. one could even incorporate a dual gang to sweep output and input blend simultaneously.

[joegagan]

getting back to the exact question you originally asked, it sounds like you are moving toward a dual path for clipping. interesting thought. why not send the high through its own fuzz, set to super saturation, then blend at output using all the common methods. pay attention to phase, tho.

you can distort the lows like a regular FF does and control gain on this, should give a very wide range of tones.

[Chugs]

You can obtain less gain in the lower frequencies by lowering the size of the 20uf cap. This would be kinda similar to changing the cap on a tubescreamer that alters the corner frequency of the gain on the clipping opamp.

[ribolovec2]

Can't i just put a capacitor in series with the 100k resistor in the schematic i've posted? I've read that it essentially provides negative feedback, so a cap in series with the feedback resistor should lower the gain in the low frequencies, or am i missing something?

[PRR]

> put a capacitor in series with the 100k resistor in the schematic i've posted? I've read that it essentially provides negative feedback

It provides the necessary DC bias current to Q1 base.

> all frequency get the same amount of clipping/fuzz.

Perhaps not. The input to Q1, and Q2's emitter, are very low impedance. The low input impedance sucks-off a pickup's highs (or not, if the FF is fed from some other source). The cap on the pot at Q2 emitter shaves a couple octaves of bass at high gain.

For high-pass, you can downsize the 20uFd cap at Q2 emitter pot.

If you want a low-pass, put 10nFd to 100nFd from the junction of the 8K2 and 330 to ground.