electronics-amplifier tutorial

This is a simple microphone preamplifier circuit which you can use between your microphone and stereo amplifier. This circuit amplifier microphone suitable for use with normal home stereo amplifier line/CD/aux/tape inputs.

The circuit is based on a low noise, high gain 2 stage PNP and NPN transistor amplifier, using DC negative feedback through R6 to stabilize the working conditions quite precisely. Output level is attenuated by P1 but, at the same time, the stage gain is lowered due to the increased value of R5. This unusual connection of P1, helps in obtaining a high headroom input, allowing to cope with a wide range of input sources (0.2 to 200mV RMS for 1V RMS output).

P1         : 2K2 Potentiometer
R1,R2,R3   : 100K
R4         : 8K2
R5         : 68R
R6         : 6K8
R7,R8      : 1K
R9         : 150R
C1         : 1µF/63V
C2,C3,C4   : 100µF/25V
C5         : 22µF/25V
Q1         : BC560C
Q2         : BC550C