The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 9-30VDC. If you don’t build the impedance adapter part with T1, you get a micamp for higher impedance microphones. In this case, you should directly connect the signal to C7.

mic ampR1 15k
R2 150k
R3 2k2
R4 820
R5 680
R6 10k
R7 10k
P1 1M

Name Value
C1 3k9
C2 100u
C3 22u
C4 4u7
C5 470u
C6 10u
C7 100n
C8 47u UNIPOLAR

Name Value
U1 TL081
D1 1N4148
T1 BC109
CN1 SIL6

mic amp