This is a microphone pre-amplifier circuit that use discrete components. The gain of this circuit is 100 and should be enough for most microphones. It is set by the ratio of the 10k resistor to the 100R. As common-emitter amplifiers, This circuit uses two directly coupled transistors. Here is the schematic diagram of circuit:
Please note that this circuit has no bias voltage source, so you can’t use with condenser type microphones. You can use this circuit with dynamic type microphone, or condenser electret module with active circuit inside (any microphone which is equipped with battery inside can be used).