I derived the attached design from experimentally trying this Circuit to make an electret microphone simulate a carbon microphone and Andy AKA's electret microphone amplifier design, neither of which had sufficient output when tested in the aircraft, and experimenting with schematic changes and component values in LTSPICE.
The attached design works though the output is lower than required when using a normal voice, but when speaking very loudly the output level matches the output level of commercially available aviation headsets and the signal is still very clear and intelligible. This tells me this amplifier can easily drive the aircraft radio's input but lacks sufficient gain to be driven by this microphone.
My previous attempt used a single 2N3904 (measured hFE = 110) and had the same problem of low output. Replacing the 2N3904 with an MPSA13 darlington (hFE = 5000) had no noticeable effect on the amplifier gain. I don't know enough about this stuff to understand why. How can I increase the amplifier gain without adding another transistor stage before the MPSA13? Cost isn't a factor but component count is as this amplifier will need to be made much smaller, and it seems absurd to require another stage when the MPSA13's gain is already so high. What am I missing?
I don't have access to an oscilloscope to measure actual signal levels and can only test each design in the aircraft, so there's a lot of guesswork involved. Any help will be greatly appreciated.