This is my modded Si Tonebender 3-Knobs.
Since the collector resistor of the darlington pair must be modified, I tried something new:
I replaced the 3k3 resistor with a 5k-A pot wired as a standard gain control, increased Q1,2 collector resistor to near 33K to get 4V, and no pot before Q3 base.
Q3 needs a resistor from C to B because silicons have almost no leakage. I set it to near 390K to get 2V at the collector. The junction of the two 10k and the 18k is at 4V (not at 4.5v since some current goes to the 18K).
With this values I had best tone.
The germanium diode is useless since silicons do not drift away with temperature. It can be replaced with a resistor of about 1M, or omitted.
Enjoy.
(http://www.geocities.com/guitarfxs/images/tonebender_mac3_si.gif)
mac
Looks good.