Chuck D. Bones
Circuit Wizard
I have messed with this one on-and-off for a long time. I finally get why this pedal is so popular. Great tones IF you can find the right knob combos. I've seen the various mods, such as Aion's Flare, PCB Guitar Mania's OctoFactory and Pedal PCB's Fuzz Foundry Deluxe. Here's my take on it. I followed a minimalist approach, in keeping with Mr. Vex's design philosophy on the original pedal.
First thing I did was add in the BASS & TREBLE controls. I tried the Flare's circuit mods, but the sweep of the BODY (BASS) and TONE (TREBLE) knobs weren't quite right for me. TREBLE could be A10K, however it doesn't go quite as bright as A25K. Next up was adding the HEAT knob so I could control the first stage gain. It does more-or-less what the Flare's SOFT knob does, but with two important differences. HEAT has more range and and it decreases the pedal's input impedance when HEAT is turned up. SOFT decreases the pedal's input impedance when it's turned down. This circuit is very responsive to the guitar knobs, especially when HEAT is dimed.
Analysis showed me that there was a huge mid peak when BASS, HEAT & DRIVE are dimed. R5 fixes that at the expense of a couple of dB gain.
Next thing I did was fiddle with the pot tapers. All of the original Fuzz Factory knobs are very touchy at one end or the other. STAB, COMP, DRIVE & GATE were all changed to C-taper. STAB was still very touchy between 9 & 10, so I dropped it to C5K. There's not much going on below 3, so I figured C5K vs C10K was a good trade. Even with C-taper, DRIVE was still very touchy between 9 & 10. So I dropped that one to C5K also and changed how C5 is connected. Now DRIVE does not go as low as in the Fuzz Factory, but that's ok because with the HEAT knob, we can get the overall gain as low as we want, assuming anyone wants to even go there. When I put C5 in series with DRIVE, the DC resistance between Q3-E and Vcc increased from 5K to 10K. So I changed COMP to C5K to get the DC path back to the right resistance. COMP has the same range as the original pedal.
I added C2, C6 & C9 to throttle the harmonics above 5KHz back a little. If the circuit is not harsh enough for your liking, reduce or remove C6. I added C11 to limit the oscillations to the audio range when STAB is turned down.
Through a few days of listening & playing tests, I adjusted a few capacitor values.
I found that I liked medium-gain Ge trannies for this pedal. I tried a few and landed on the MП20s. The ones on my breadboard have HFE around 60 (Q2) and 100 (Q3). П28s also work well. If I had some AC128s, I would have tried those too.
One of the things that surprised me about this circuit is how stable the bias is with Ge transistors. I chalk that up to the fairly low leakage (Q2 Iceo = 47μA)
Total parts count, not counting LED, pots, switch or jacks is 25. I'll be making a Vero for this. If there was ever a pedal where the statement "all component values are negotiable" is true, it's this one. Hell, half of the resistors are knobs.
I changed a couple of part values since this pic was taken.
The white knobs have the original Fuzz Factory functions. The colored knobs are my additions.
L-R: LEVEL - TREBLE - STABILITY - GATE - COMP - DRIVE - BASS - HEAT
First thing I did was add in the BASS & TREBLE controls. I tried the Flare's circuit mods, but the sweep of the BODY (BASS) and TONE (TREBLE) knobs weren't quite right for me. TREBLE could be A10K, however it doesn't go quite as bright as A25K. Next up was adding the HEAT knob so I could control the first stage gain. It does more-or-less what the Flare's SOFT knob does, but with two important differences. HEAT has more range and and it decreases the pedal's input impedance when HEAT is turned up. SOFT decreases the pedal's input impedance when it's turned down. This circuit is very responsive to the guitar knobs, especially when HEAT is dimed.
Analysis showed me that there was a huge mid peak when BASS, HEAT & DRIVE are dimed. R5 fixes that at the expense of a couple of dB gain.
Next thing I did was fiddle with the pot tapers. All of the original Fuzz Factory knobs are very touchy at one end or the other. STAB, COMP, DRIVE & GATE were all changed to C-taper. STAB was still very touchy between 9 & 10, so I dropped it to C5K. There's not much going on below 3, so I figured C5K vs C10K was a good trade. Even with C-taper, DRIVE was still very touchy between 9 & 10. So I dropped that one to C5K also and changed how C5 is connected. Now DRIVE does not go as low as in the Fuzz Factory, but that's ok because with the HEAT knob, we can get the overall gain as low as we want, assuming anyone wants to even go there. When I put C5 in series with DRIVE, the DC resistance between Q3-E and Vcc increased from 5K to 10K. So I changed COMP to C5K to get the DC path back to the right resistance. COMP has the same range as the original pedal.
I added C2, C6 & C9 to throttle the harmonics above 5KHz back a little. If the circuit is not harsh enough for your liking, reduce or remove C6. I added C11 to limit the oscillations to the audio range when STAB is turned down.
Through a few days of listening & playing tests, I adjusted a few capacitor values.
I found that I liked medium-gain Ge trannies for this pedal. I tried a few and landed on the MП20s. The ones on my breadboard have HFE around 60 (Q2) and 100 (Q3). П28s also work well. If I had some AC128s, I would have tried those too.
One of the things that surprised me about this circuit is how stable the bias is with Ge transistors. I chalk that up to the fairly low leakage (Q2 Iceo = 47μA)
Total parts count, not counting LED, pots, switch or jacks is 25. I'll be making a Vero for this. If there was ever a pedal where the statement "all component values are negotiable" is true, it's this one. Hell, half of the resistors are knobs.
I changed a couple of part values since this pic was taken.
The white knobs have the original Fuzz Factory functions. The colored knobs are my additions.
L-R: LEVEL - TREBLE - STABILITY - GATE - COMP - DRIVE - BASS - HEAT
Last edited:
