I have modified johnk's original layout to include 3 mods: Resonance, Attack and Decay. (Mods suggested by Mark Hammer on DIY and noted at GGG)
The nice thing about these mods is not only are they all effective, they are easily bypassed.
Resonance: It was suggested to add a 100k pot in series with the 430k feedback resistor. I found 100k was to much and caused a distorted oscillation just after mid point (with the Range turned past 2 o'clock). I went with a 50k so the entire range of the pot would be useful regardless of the position on the Range control. Turning the pot fully counterclockwise bypasses this mod.
Attack: Add a 1K pot between D2 and positive side of C4. Slows the attack just the right amount. Turning the pot fully counterclockwise bypasses this mod.
Decay: Switch in additional capacitor(s) parallel to C4. 4u7 and 10u were suggested values. I originally was going to use a DPDT on/off/on to choose between either additional cap, with the center position bypassing the mod. But I found the additional 10u was a bit to long of a decay for my taste. I went with just the 4u7 mounted on a DPDT on/on switch to either add in the extra cap or bypass it.
I also socketed the 2M2 resistor and the 100n at the Range pot, lug 2.
2M2 resistor: This value suggested by GGG increases the usefulness of the Range pot. I tried the original schematic's 470k and the Range pot was only useful the last 1/4 turn or so. With the 2M2, the entire range of the pot is useful and the effect seems more lively. However, the 2M2 resistor adds a bit of noise with the Range pot fully clockwise, which was the same result with a 1M8 and a 1M5 resistor. I stuck with the 2M2 as the additional tones from the Range pot are worth it (just can't go past 9 on the pot)
100n cap: It was suggested increasing this value would help track lower notes better without adding additional lows to the output. I tried 220n and couldn't hear the difference, all notes tracked well with my Les Paul & Tone Zones, so I stuck with the 100n. Maybe it's useful for bass players, I don't know.
End result, added versatility to this excellent envelope filter. This pedal is a lot of fun and sounds great. Definitely a keeper.
Verified by me
1978 Gibson Les Paul Standard, Cherry Sunburst, Nickel Tone Zone & Air Norton Pickups, Sweet 16 wiring
How'd you say it sounds compared to a Snow White? I really like the Snow but damn it it's a big bitch. So far it's my favorite of all the envelope filters I've researched, but if I can avoid the big board I will. (I like simple circuits with lots of functionality.) I'm asking as a bassist if it makes any difference, idk if you have any opinion in that sense.