I always wanted to build this one but the schematic seems to have some errors in it. So I started to tweak it a bit to make it work like the original according to demo videos online. I also added a "Pre Amp" setting.
- Output level in Scoop Mode is much lower than the others, by increasing R39 (22k) across the base of Q5 and and ground to 910K increased the output quite a bit without changing the character of the distortion. MPSA05 is a low gain npn si, you could replace it with a high gain npn si like 2N5088/MPSA18 to increase the output even more. I used a 2N5089 here and now it's almost as loud as the other modes.
-The Dual J FET mode was lacking quite a bit in gain so I decreased R30 from 100k to 8,2k, I found that values between 4,7k to 10k sounded good here. You could even solder a jumper here for even more gain but it's becomes quite noisy.
- Tonestack didn't worked for me as drawn. Changed connections to the Eq pot to work as a Big Muff/Fuzz War 2 tone control.
- Since I used a 2P6T Rotary I added a "pre Amp" setting by take the signal straght from the tonstack to the volume control just like in the Colorsound Jumbo Fuzz. Output is lower than the other settings but it gives you quite a nice overdrive.
I think that that was it. Some more modifications could probably be done but I'm quite happy with it as is.
Cheers