Having a lower output than most other condensers, the C-37A can also be used on very loud sources like guitar amplifiers and drums without worry of clipping the mic preamp due to a crazy-hot signal. These quirky mics are capable of both directional (cardioid) and non-directional (omni) pickup by opening and closing a port to the rear of the capsule with a small screwdriver. The C-37A uses a cathode follower design and 6AU6 tubes which must be very carefully selected for noise and microphonics, and the output transformer is actually located in the power supply. The earliest models used hand-wired power supplies, later models went to PCBs and added an additional high frequency cut to pair up with the switchable bass rolloff.