I love Big Muffs, you love Big Muffs and Skreddy definitely loves Big Muffs. Marc has produced so many great sounding Big Muff variants that you could say he's the "goto" guy for getting a great Muff type tone.
Here's one of his latest offerings - the P19. Here's his description from the Skreddy Site:
"Specifically tuned to the sound of a block-buster 1979 album and emulates the "magic" 70's era fuzz pedal that was somehow clear and articulate on high notes while still fuzzy and aggressive on low notes, without excessive low-end muffiness or high-end fizz. The mids are scooped just enough to keep it from sounding congested, the lows are rolled off just enough to keep it from sounding wooly or boomy, and the highs are gentle, present, and well balanced.
Its clarity will encourage you to dig in and express yourself; it's not an overwhelming "wall of fuzz" type effect.
A wide variety of aggressive and clear-sounding applications, particularly excelling in sustaining, biting, legato lead work"
May I suggest that the "block-buster 1979 album" is "The Wall" by Pink Floyd? Just from that you should get an idea of what this pedal is aiming at - Comfortably Numb? Yes please! In fact, here's what Marc himself has said regarding the P19 design:
"Pretty much started this project by approximating the Cornish P1 (sans input buffer) but tuned it to my ear and preferences--a few ceramic caps here and there, carbon comp resistors, some minor resistor value tweaks, smaller input caps to both help articulation and reduce 60 cycle pickup hum, and a big .33uf cap (instead of typical .1uf) between tone stack and output stage to help the bottom end breathe, as it is tight in the lows.
It's really not a P1 clone, just used that as starting point/guide to help me capture the right balance of clarity and aggression to nail The Wall tones, which I've always found challenging and irresistible."
To just convince you that the P19 really can get the tones it claims, here's a demo video for you:
Now Marc is a generous guy and he posted up the schematic over at freestompboxes.org;
You can build this on nearly any Big Muff layout around, as long as you check you make the correct parts substitutions you'll be fine ;-)
Regarding the diodes (which are unmarked on the schematic), here's what Marc has to say about them:
"Basically. I have a special "Skreddy" recipe for my clipping diodes for the slightest touch of asymmetric clipping that doesn't sound so different in the final mix (after 2 stages of clipping), but just adds a little bit of depth and character. I'd like to reserve that one last piece of info as my own signature touch. I suspect that older Big Muffs might coincidentally share a similar profile because older diodes were probably less precisely made and matched back in the day (much like older transistors tend to vary hugely in gains compared to their new counterparts)."
So, what you choose is up to you! On this gut shot they look very much like 1N4148 type diodes:
I imagine a pair of slightly mismatched 1N4148 type diodes will get you right into the correct ball park...
Finally, here's the Freestompboxes.org forum topic for reference: http://freestompboxes.org/viewtopic.php?f=7&t=16382