A while ago. Chris Stelloh sent me a Death by Audio germanium Filter to trace. The trace went pretty smootly and I sent the schematic to Chris and he made a vero layout out of it. However, this circuit requires some transistor and diode picking to work as intended. See Chris's notes below...
My notes + warnings from my build attempts: PROCEED WITH CAUTION.
1)
The transistors: DBA used MP10b NPN germanium transistors which have a
common hfe range of 20-50. The lowest gain transistors I have on hand
are MP35's around 40 hfe. And none of these worked properly. At lower
settings, the gain was sputtery and sounded misbiased. I was able to get
the circuit to work properly with some NPN Fairchild silicon dots from
Small Bear that measure at 25 hfe.
2)
The unknown silicon diodes on the mosfet gate: 1n4001-4007 worked quite
well. I had my best sounding results with 8.2v Zener diodes. the 9v
supply will cause any Zeners with lower than that rating to heat up and
pop.
And here is layout with trimpots for the collectors solve the gating issue when the Gain control is turned counter clockwise. I also ditched the internal trimpot in favour for an external volume control.
