The microphone preamplifier described here is a ‘hybrid’ passive / active. A small transformer input provides a small contribution to the gain of all (about 10 dB), and a transistor provides the additional gain (35 dB) for normal use with a small dynamic microphone. About 40 kHz bandwidth, small and simple installation that requires little space.
Power supply : It is not unusual, it chose the power of 24 V. The reason is that we want to have a module with a fixed gain and not adjusted. if your also want to use the microphone low output signal amplitude your can lower the supply voltage to 15 V or 12 V. Make all the same tests with 24 V and 12 V, just to see whether you notice a difference in the sound …
