Fuzz Face "fuzz" pot question for you.

[Steel Curtain]

Hello all!

        OK, This is likely a dumb question, but I don't know the answer!


If a fixed fuzz level is wired like this....





Why is a variable fuzz wired like this...






But not like this? ....





I'm a noob and am not set up to breadboard yet.  Are both of the later wiring diagrams two ways of doing the exact same thing?

thanks all

[PRR]

"B" keeps the DC conditions but changes the AC (audio) conditions.

"C" changes the DC conditions but does not change the AC (audio) conditions.

We normally want the DC conditions somewhat constant, and tamper the audio conditions to change the sound.

> am not set up to breadboard yet

Fix that. EXPERIMENT. You don't need a breadboard; in this case you could just move a few wires on any typical fuzz.

[Thecomedian]

What he said. You're reducing the AC's current or amplitude as it races around the circuit, bringing the transistor out of saturation and cutoff.




This isnt completely the same circuit, but that sharp zig zag blue line is the line from ground though the parallel pot/cap to Q2(in this case, Q1) and the feedback line to Q1 (in this case, Q2).

It's much smoother. a normal fuzz face would have undistorted sine wave at the output (the green wave).

[fuzzymuff]

"B" keeps the DC conditions but changes the AC (audio) conditions.

"C" changes the DC conditions but does not change the AC (audio) conditions.

We normally want the DC conditions somewhat constant, and tamper the audio conditions to change the sound.

> am not set up to breadboard yet

Fix that. EXPERIMENT. You don't need a breadboard; in this case you could just move a few wires on any typical fuzz.

So "C" is how you would wire for a Bias control?

[EATyourGuitar]

bias is a 5k or 1k pot on the collector with all the fixed resistors selected so that your collector will be half your supply with the pot in the middle of its range. any change in temperature throws a germanium fuzz face off bias. that pot will allow more or less current to get down to the collector and hopefully bias it again after the temperature has changed.

[Steel Curtain]

Thanks guys..

            I see now that my next step is to research the effects of the DC and AC has on the sound. Sadly, I can't make much sense of the illustrations posted by TheComedian. I suppose in time I'll understand them more. Is there a book or website that you guys recommend for related research?

           And I have a breadboard and some components but I'm waiting on the transistors that I ordered to come in before I can get going.


I've been researching how these work, especially after I found that a few pedals have a unique way of controlling the dirt in these pedals..

For example...





The first is from a classic VOX version of the fuzz circuit and the second is from a somewhat popular current production pnp fuzz that I like the sound of. I like the dirt on this one.

I don't know for sure the rules here on posting schematics on current production pedals, but It's a LOVEly PEDAL. I could PM the schematic if someone wants it. Or just post it up if it's allowed.


Thanks all

[Thecomedian]

in the bottom right is the "pot" and cap. the pot is simulated in LTspice using two resistors in series with the cap in the middle, such that changing the values on the resistors will let more or less AC current through the cap, but keep the total resistance for DC current a static 1k (or 1001 in this case).

"Turning the pot" aka changing the resistor values so more AC comes through the cap, the bright green line becomes more smooth, less clipped and so on. The Dark blue line goes from being a triangle wave to an almost unclipped sine wave. It's clipping that causes distortion. This is how the AC current affects the bias of the transistors through the potentiometer that is meant to "control the fuzz", through the cap, making it either distorted, or turning it all the way down and having no distortion (because the AC current is getting as much resistance as the DC current).

in this version, the pnp, the current/electrons are moving from the battery, through R2 and R3, through Q1, through the 1k (or 1 ohm resistor) and then through the cap at the bottom.

in the npn version, current/electrons are moving through the cap, through the "pot", through Q1, through R3, then through R2.