The circuit below is a Dynamic Mic Compressor circuit which is simple, easy to built, inexpensive but the results are quite satisfactory. Audio output sounded outstanding.
The principle of this circuit is very simple, the first transistor is used as microphone pre-amplifier. Then a second transistor used as a buffer. And the third transistor is a feedback circuit. A very sensitive electret microphone used in this circuit.
Supply voltage of this Dynamic Mic Compressor circuit must be 12 Volt. Highly recommended to use its own power supply, do not use a shared power supply from another electronic circuit module. Regulated circuit with fine/good cable and good grounding is recommended to minimize hum.