I again revisited the concept of a low noise audio amplifier. The excellent Op Amp noise calculator suggested that the NF of my amplifier was 26dB. Now that got me thinking: pretty any random mmic has a NF of below 6dB. So why not use a mmic rated to work from DC upwards as a front end?
I didn't have much luck finding any prior work in using a mmic as an audio amplifier. But it did trigger the recollection that Direct Conversion receivers use low noise audio amps and that "Solid State Design for the radio Amateur" had used an all transistor amplifier in a conceptual DC receiver.
That evening I sat in front of the TV with a calculator and during the commercial breaks reworked the biasing for use with a 9V battery and reduced the overall voltage gain to 1000. That should allow me to see input noise levels down to perhaps 5uV. I ended up with the following:
Unfortunately my amplifier was a very good oscillator when the input was shorted or terminated in a low ohm resistor. I haven't been able to stop the oscillations so a different amplifier is going to be built.
73's
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