How to build Low impedance microphone amplifier

Description
The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 6-30VDC. 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.

Schematic diagram

Layout of board

printed PCB

Parts
R1=15k
R2= 150k
R3= 2k2
R4= 820
R6= 10k
R7= 10k
P1= 1M
C1= 3k9
C2= 100u
C3= 22u
C4= 4u7
C5= 470u
C6= 10u
C7= 100n
C8= 47u UNIPOLAR
D1= 1N4148
U1= TL081
CN1= SIL6