Chuck D. Bones
Circuit Wizard
Phill in Perth sent me a link to the Box of Germanium layout. It's basically a Zvex Box of Rocks with the MOSFETs replaced by low-leakage Ge transistors. A clever idea.
I wasn't happy with the biasing and a few other things, so took the basic idea and ran with it. This is the current incarnation of my breadboard. I first tweaked the biasing and increased the collector currents. I added a BASS cut between the 1st & 2nd stages. I moved the TONE network between the 2nd & 3rd stages and retuned it a bit. I added a gain switch (CRUNCH) to the 3rd stage. To prevent the 3rd stage from loading the TONE network, I added a JFET source follower (Q3) in a Darlington configuration. With CRUNCH in the middle (low gain) position and GAIN turned down, it plays clean. Turning up GAIN and/or flipping the CRUNCH switch allows the user access to varying levels of dirt and sustain. A lot of different Germanium transistors will work; this is what I have installed at the moment. Q4 does not need to be low-leakage. I wanted very low leakage and high gain for Q1 to minimize noise. As GAIN is turned up, the 1st stage EQ becomes more mid-focused. Due to the low input impedance at moderate to high GAIN settings, it is very responsive to the guitar's volume knob.
This thing is sounding pretty good as drawn. I think I'm done tweaking it. As usual, all component values are negotiable.
Knobs (L-R):
Black - LEVEL
White & green are part of a different circuit, ignore those. All that stuff in the upper left is the Big Cheese wired for Cheese Mode.
Switch - CRUNCH
Red - TONE
Purple - GAIN
Blue - BASS
Q1 is upper right, Q2 is lower right, Q3 & Q4 are lower left.
I wasn't happy with the biasing and a few other things, so took the basic idea and ran with it. This is the current incarnation of my breadboard. I first tweaked the biasing and increased the collector currents. I added a BASS cut between the 1st & 2nd stages. I moved the TONE network between the 2nd & 3rd stages and retuned it a bit. I added a gain switch (CRUNCH) to the 3rd stage. To prevent the 3rd stage from loading the TONE network, I added a JFET source follower (Q3) in a Darlington configuration. With CRUNCH in the middle (low gain) position and GAIN turned down, it plays clean. Turning up GAIN and/or flipping the CRUNCH switch allows the user access to varying levels of dirt and sustain. A lot of different Germanium transistors will work; this is what I have installed at the moment. Q4 does not need to be low-leakage. I wanted very low leakage and high gain for Q1 to minimize noise. As GAIN is turned up, the 1st stage EQ becomes more mid-focused. Due to the low input impedance at moderate to high GAIN settings, it is very responsive to the guitar's volume knob.
This thing is sounding pretty good as drawn. I think I'm done tweaking it. As usual, all component values are negotiable.
Knobs (L-R):
Black - LEVEL
White & green are part of a different circuit, ignore those. All that stuff in the upper left is the Big Cheese wired for Cheese Mode.
Switch - CRUNCH
Red - TONE
Purple - GAIN
Blue - BASS
Q1 is upper right, Q2 is lower right, Q3 & Q4 are lower left.
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