Notice: some of these are older circuits. I've checked and updated them but there still might be things I'd do differently today, so if you point those out I might agree with you.
Let's start with everyone's favorites: the circuit covers!
- Violets are Blues. A Bluesbreaker variation with scaled down impedances for lower noise, standard values, added recovery stage for low output impedance, no phase inversion and more output. The original marshall box is a good circuit, except for the shortcomings covered by the added stage, I like it. I wanted to give an alternative to the two most popular derivatives though: with respect to the Morning Glory the added stage uses a MOSFET instead of a JFET, which is cheaper to get. I usually avoid MOSFETS but here it's a good choice since the noise isn't an issue after the "damage" has already been done by the rest. Same gain and bias otherwise, which might add a bit of clipping and justify any difference with the original. The second version is a competitor to the (insert royalty) of Tone, values wise, but again with impedances scaled, only E6 values, and again the added recovery stage, this time adjusted for more headroom so it doesn't clip. If you want something closer to the original Bluesbreaker, build the first but with the MOSFET values of the King's.
Frequency response vs gain of the two:
Tone control reworked to use a 10k pot is very close:
demo of the first version: - 1Q81. The name is inspired by a novel you might know. I wanted to make a 1981 but using just a dual op-amp. The focus was on using few parts and standard values without changing the result. I'm particularly proud of the buffered bypass scheme. the 5088 has been chosen to provide good input impedance while keeping a good bias. My first attempt was to combine the two gain stages into one, but as they are they provide a frequency response that is difficult to match along all the gain pot travel, at least with a single gang.
demo: - Feathers. Same philosophy as the above, applied to the YATS Plumes. I feel compelled to rework circuits when so many people show interest in them, even if I don't find them particularly interesting. And I try to account for, point by point, all the observations about it sounding different than the original. In this case a major one is the beloved headroom, since I decided to remove the charge pump. To complement the observation in the image, headroom depends on gain for an arbitrary output amplitude. Since the contribution to the frequency response of C1 and C3 is minimal at low gain, it's possible to achieve the same headroom (or more) just by lowering the minimum gain, at the expense of output. Diodes are in both cases the limit on headroom, so the supply voltage doesn't even factor in for the first stage. I also made this so that it's just values away from a bufferless TS so you can use any board or layout you like. I did end up making my own layout though.
- Plastic Timbre. An optimized version of the Plexitone. As always, focus on using few parts and standard values. The input buffer on an high gain pedal always bothers me, it's free added noise ready to be amplified. The clipping stage has been scaled down to use 4148 instead of red leds, with gain reduced by their ratio of Vf, with the frequency response kept the same, again to cut down on noise. The gain switch has been rewired so that at any moment there's negative feedback. The tone control is interesting I'd say: since the op amp is at virtual ground, the same response (save a bit extra range on the treble side) can be obtained with a passive tone control. This avoids the phase reversal so that I can combine this and the next stage into a noninverting one. Again no charge pump needed. That's another reason for scaling the first stage to 4148: less output and no clipping, actually less than in the original even if for some reason you decide to max both gain and boost . The recovery stage gain has been chosen for a good output without clipping.
The boostless version simplifies the circuit even more, making it a 3 knob distortion with all the same sounds still there, just less stomp switches:
demo: - Dual op-amp RAT. This one came out right after the plastic, since at that point I figured I had a template for any hard clipping distortion. The already featured Type C. OD also came out of this batch. The RAT lends itself perfectly, since nobody has time for single op amps, and more importantly this replaces the jfet output buffer that, while I'm glad it's there, is another nuisance in this day. If you are a fan of the LM308, run away from this one! Again, the second stage gives just enough make up gain to have good volume at noon without clipping.
- Quick shave. A much simpler version of the Fairfield Barbershop. A friend of mine, who has tried both, is a big fan of this one. Main focus is reducing parts count, like the stopper resistors and the reverse polarity protection. The output buffer isn't there for the same reason. You can add it, but output impedance in the original was a bit spoiled anyway at low frequencies by the small output cap. I've also made the drain trimmers explicit since the hand-picked resistor values of the trace seem to be taken a bit too literally.
- Trimmed face. This is nothing surprising, but I like it as collection of "quality of life" Fuzz Face mods, like the trimmable bias (you can make it a pot and it's fun!); the bandwidth limiting caps that work well at suppressing high frequency or ultrasonic oscillation that often haunts this circuit when made with higher bandwidth silicon transistors, and you can maybe hear as a "sizzle" on the note decay; the input series resistor which both tames the sometimes excessive gain of a silicon fuzz face, usually tamed by turning the gain down a bit, but also gives a strong and reliable input RF filter and makes the circuit somewhat more tolerant of low impedance sources if you want. Also I made the volume pot and output cap 100k and 10u because they have very little effect on circuit operation and this gives a decent output impedance which is more than worth it for me.
And the version that came first, featuring PNP but negative ground, which was the original goal. All the things here actually started as attempts to tame this circuit, that tended to oscillate in certain situations. PNP negative ground is possible, but YMMV, there still might be some oscillation at certain settings like minimum volume on the guitar (not coincidentally the fuzz factory includes a PNP negative ground fuzz face. You can have fun with it!).
demo: - Fuzz Facelift. I'm not done with fuzz faces it seems. This one's goal is to keep all the classic cranked gain tones while making the ill-treated gain knob more useful. This is accomplished by moving the gain control to the first stage. When maxed, you have a classic, low input impedance, high gain fuzz face, because the emitter is effectively grounded. At low gain, the input impedance rises to something close to 200k or more, hopefully giving an interesting sound without the usual dulling that happens. Last but not least, this one doesn't need trimming! the emitter resistor assures predictable bias even with widely differing beta. You can still make it adjustable if you like to mess with it. Care has been taken to avoid blocking, since we're adding capacitors. With these values, blocking is roughly the same as with the original.
demo: - CryMan. This is when Cry Babies grow up. This is meant as add on to a commercial wah, with the additional parts inside the boxes. The added feature are switchable range between stock, JImi and bass; variable Q with stock at center (I really like the lower Q); a dry blend circuit which exploits the buffer already in the wah, useful with bass but also with guitar for modulation-type sounds; buffered output which prevents oscillation when used in front of a Fuzz Face.
- Fuzzed Green ringer. This is a simple mod to the green ringer which makes it an unruly fuzz. The mod itself is just bypassing the emitter of the first stage, but the circuit here has compensated gain to match the original gain at minimum and more standard values which you might enjoy using even in a standard green ringer build. You can also just make the gain switchable.
I take no credit for the name, it was chosen by the person I made this for. For my part, I only know the term can have a broad range of meanings, and this being a derivative work it fits in a way. - Fuzz factory...7? This my collection of useful mods to a fuzz factory, which then I discovered match the control set in the fuzz factory 7, so I feel validated in their addition. The capacitor switch is a known mod, and I'm a fan of the unofficial "thin" position, which makes the pedal something different from a noise machine for once. The other addition is the tone control, which lets you get more normal or smooth sounds without compromising the good output impedance. There are also other optimizations, like the use of a 10ka volume pot instead of 5kb+stopper, which should give a more usable volume control and saves one part and the suggestion of a rev log gain pot.