Pre microphone model Low impedance circuit,that interesting. Because be the circuit has small-sized. It uses integrated number circuit TL084 be op-amp kind low noise. Then of good quality good sound , besides if you have no Microphone still can use 8 ohm loudspeakers can replace. By use transformer , build add follow circuit picture. This circuit should apply to power supply the quality is tall for decrease all noise.
Dynamic microphone Amplifier for earphones
ECM Mic Preamplifier by BC549
Portable Microphone Preamplifier by BC550C
Microphone Preamplifier by LM837
Simple microphone preamplifier by BC547