I just wanted to post my build here. at the DAM forum it didn't get much love, but those guys in that thread are PROS and meticulous, I guess the stuff in mine is slightly crooked here and there, need to get more meticulous about that.
I can say that a lot of what's been said here is true. It's hard to find the right transistors for a good sound without all the fizzly stuff, and on top of that the biasing process is VERY sensitive, and between Q1 and Q3 you have to get BOTH of them right at the same time to get the right sound... took me forever. I used IvIark's layout with the trim pots...I don't see how people do it without them, unless they're doing it on breadboard first before building. I ended up with a 49 hFE 2N404 in Q1 (this part really seemed to bring the sound to life), a 115 hFE 2N404 in Q2, and a 139 hFE AC128K Tungsram in Q3. I ended up taking notes of the voltages from base to ground on Q1 and Q3 once I found the right trim pot settings, which I could offer on here, but I haven't tried using the same settings with another transistor set so I'm not sure if they're universal. Basically I just started with the trim all the way in one direction until there was no sound happening, and then bring it up slowly until just the point where you start to hear the "sizzly fizzlies" and then back it off just a tiny bit from there. There WILL be a slight gating effect on quieter pick attack playing, but I think this is just part of the character of the sound of this circuit, and it sounds nice in a certain way, a lot like the Penny Pedals Fingerprint circuit. I've come to like that sound.
I had to change the 2.2M in my build to 1M to get unity gain with a strat, and for me the ideal value was to lower it to 100K for a "typical" amount of extra volume available on the Level control. I don't think this changed the tone too much other than reducing the gating slightly (which is a benefit) but I'll have to do an A/B with the 1M to see if there is any tonal shift happening. You can jumper that resistor too but then the level is over the top and out of hand.
Humbuckers indeed seem to overload the input of this circuit and create a sag or "squish" sound, which can be used musically for effect on heavy strums. I've found it works best with low/vintage output pickups, or tweaking the volume knob on your guitar as someone else mentioned.
This is a nice sounding circuit, I'm glad I have it around, now. Very "earthy" in the eternal words of Gearmanndude
it did need a pulldown resistor on the input for footswitch popping