Ta-Da! I ended up breadboarding two very similar versions of this circuit (see below). It started out as 4 gain stages, with hard diode clippers and a volume recovery stage at the end. Way too unruly. Cut back to 3 gain stages, similar to what you see here, still had the hard diode clippers and a volume recovery stage. Decided I didn't like the hard clipping, so I removed the diodes (they were in parallel with C9). The signal was much larger without the diodes, so I ditched the volume recovery stage. The first version had all Si BJTs. Then I tried some Ge transistors for the 2nd & 3rd stages. Didn't really hear a difference. When back to Si and switched to JFETs for the input and gain recovery stages, mainly to reduce the parts count. I finally settled on V2.3 below. Tried Ge once more for the last stage, no real sonic diff, then a MOSFET. The MOSFET does sound a little different, hard to describe. Tried tuning the TONE control for mid hump, mid scoop and flat in the middle. Ended up with flat. Treble boost is fairly mild and starts in the midrange. Treble cut smooths out the hair without getting too dark. I also played around with the coupling capacitors (C3 & C6). The ones in there now let some bass thru without getting too muddy. If you want sludge or some deep bottom-end for playing bass thru it, then increasing C3, C4 & C6 will get you there.
Development tools I used were Duncan's Tone Stack Calculator, LTSpice, breadboard, USB scope, headphones and a Strat. Oh, and a big pile of parts.
Here's how it all works:
The first three sections of the FUZZ control (VR1) varies the gain & bias on each stage. The last section of the FUZZ control (VR1D) is a Presence control that cuts back the top end as the gain is turned up. Because VR1 is all linear taper pots, I had to install series resistors smooth out the gain variation at the low end of the resistance range. The FUZZ control is very smooth now and goes from clean at 7:00 to mild overdrive around 10:00 and gets progressively nastier from there. Total gain adjustment range is 40dB. The TONE control is similar to the Foxx Tone Machine, just tuned differently. Basically a BMP tone control with one resistor removed.
1st stage is a simple JFET boost, with a variable drain resistance to adjust the gain and headroom. Has a little over 30dB gain with FUZZ dimed. C2 rolls off the top end a little at max FUZZ. Most JFETs will work, you can compensate for different Vp by adjusting R5.
2nd and 3rd stages are very similar to the Quarantine Fuzz. Their gains and bias points are adjusted via the pots in their emitter paths. R9 & R14 limit the max gain; R13 limits the min gain. Any high-gain, low noise NPN transistors will work. Any N-channel MOSFET will work for Q3 in ver 2.4; tune the bias range with R11.
Is it a great pedal? It's OK, it's no Mojito or Biggus Dickus. I'll probably end up making a Vero and stuffing it in a Handy Box just for fun. It's been a fun diversion during lockdown.
View attachment 8117
View attachment 8122
View attachment 8121
tagboardeffects.blogspot.com
