I got more data on the 1N270 which says that it is a Gold Bonded Germanium, with minimum forward voltage and current similar to a Schottky diode.
The reverse current on the other hand is 100uA as compared to the 1N5711 you folk recommend which is 1uA. The later would be a better choice on small signals. So I see what you mean now. In my circuit the impedances are low so the reverse current of 100uA would not be much of a signal in that circuit. The lowest signal of use is 0.001 A across a 10 ohm load. But the 1N5711 would be better. If amplification is used after the 1N270, before it goes to the sound card I suspect then that you fellows recommendation for the 1N5711 would be the ideal thing. 100uA of leakage in this case would be amplified up high. 1 uA reverse leakage in the case of the 1N5711 is a pretty nice figure. And I would think it would make for lower noise? To get an idea of the impedance range of this 1N5711 just forward bias it with a low voltage and potentiometer and watch the current and bias voltage over a range of operation. The range of operation would be from 0.3v to 0.5v. The impedance will be close to that of the 1N270 since the rated small signal of the 1N5711 appears to be 0.41v @ 0.001 A which is close to that of the 1N270. I looked at all of Edwardo's circuits, and he has quite a few of them now. Some ideas are cool, and similar to ideas I have had over time. He does have the same method of diode mixing listed in his circuits. The diode mixer would be easily used in the single sideband BFO section of a ham radio or shortwave receiver before the crystal filter. If the BFO can be pulled -12 kHz downwards and used as the LO IN.
