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> > The schematic suggested by Jinx
> > had just one op-amp with a variable feedback resistor
> > of 1Mohm which can deliver a huge gain (in theory).
> 
> Microphones typically need a voltage gain over 1000

Electrets are pretty easy to work with. Attached is a typical
front end from a "bug" transmitter. Very sensitive and can
pick up speech across a room, no problem. As I mentioned,
I've never needed more than one stage for amplification, either
opamp or transistor

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