The board has no amplification, only parts to adapt a capsule designed to run from a 3V battery to run from 48V phantom power.

The 3 wires from the capsule are ground and source and drain from the FET. The FET is used as a source follower with no voltage gain and output impedance approximately equal to the 6.8K load resistor, R3. ZD2 protects the source from power on / off surges. Electrolytic capacitors E1 & E2 couple the signal to pin 2 of the XLR connector.

The drain is connected to 2.6V DC supplied from pin 2 via CR1, a constant current reference of about 1 mA, regulated by 2.6V zener ZD1, and filtered by R4, C1, & E3.

R1 and E4 provide a ground reference and some impedance balance to pin 3 of the XLR. So the circuit is simple though it uses a fair number of parts. Not bad for the price.

The capsule is cardioid, with pretty good rear rejection. It sounds normal, which is good. I haven’t actually used the mics on drums, since I bought them primarily as body donors. :-) I have no doubt you could make a fine recording of a drum set with these, given a talented drummer to work with.