I would like to build a very sensitive microphone capable of picking
up extremely low noise at about 3 feet. What approach is typically
used to pick up low amplitude audio signals? Thanks.

An old crystal mic, the sort used years ago, we're very sensitive and
produced a good voltage (high impedance) for such purposes. Try car boot
sales etc. They were used with valve tape recorders.
hope this helps.
Rod

"iwhitey" wrote in message
om...
I would like to build a very sensitive microphone capable of picking
up extremely low noise at about 3 feet. What approach is typically
used to pick up low amplitude audio signals? Thanks.