Microphone Pre-Amplifier with Tone Control
Microphone can’t be directly connected to a power amplifier because the signal is too weak. Standard audio power amplifier accept about 1 Vrms to give a full volume (maximum power), and off course there’s such microphone has such high level output. To provide signal with high enough amplitude, we can use a pre-amplifier circuit shown in the schematic diagram below:
Since a DC bias is provided (5k6 resistor on the input), this pre-amplifier circuit will work for both dynamic (moving coil) and condenser types. The tone control is a passive type (the attenuation is done by shorting the signal to ground). Almost any type of NPN small signal transistor will be OK for this circuit (Ic ~ 100mA and hfe~100-300).