Microphone preamplifier is a circuit that stands between microphone and stereo amplifier. You just need to connect microphone to circuit input while output can be connected directly to line/CD/aux/tape inputs.
This simple circuit (Design and copyright Tomi Engdahl 1997,1999 ) can handle both – electret and dynamic microphones. As dynamic microphone doesn’t require power it drives signal directly to transistor amplifier, while electret requires additional power to be operational. Circuit gives about 30 – 40dB amplification depending on power voltage and transistor used. It also has a red LED indicator when circuit is ON. Mic preamp circuit also has a simple RC filter (R4, C5) that reduces potential noise from power supply. C1, C2 and C3 capacitors are used to block DC bias flow to transistor. Electret microphone gets power through R1 resistor. Circuit can be modified by adding a potentiometer to circuit output which would allow to adjust output signal level. [link]