John, VK2ETA, has used the small circuit board “SSM2167 Microphone Preamplifier Board Preamp COMP Compression Module DC 3V-5V”available on eBay or Aliexpress as a compression and mic pre-amplifier.
He simply connected the input to the mic, added a 4.7K ohm resistor between the mic input and the 5VDC (taken from the Raduino) for biasing the electret and put a 10K ohms potentiometer in the output to adjust the power level to the mic preamp stage.
He didn’t modify his uBitx board, but simply inserted the board prior to the mic input. The gain of 20dB is reduced back with the output potentiometer. John removed the “R1” resistor and replaced it with a 51K Ohms resistor to get a 4:1 compression factor, up from the 2:1 as delivered, but this change has yet to be tested “on air”.
John hasn’t received any negative feedback about the compressor except when I pushed the output potentiometer too high.
Simon VK3ELH used the same board and a similar scheme for powering the module from the regulated 5v line on the Raduino. It is also installed separate to the main board and inline with the mic input.
Simon used a 75k ohm resistor for compression and 1k ohm resistor for the noise gate and a 100k pot on output. At full output, his audio was readable but distorted based on an audio check QSO, so the output has been turned down.
He put a larger heatsink on the IRF510 to cater for the higher average output, as the stock one was getting warm!
A side effect of the mic being on all the time is that there is leakage through to the speaker and it causes some feedback if the mic is within 2 inches or so of the speaker.