The PPA (Phantom Power Adapter) is used to connect the OKM to 48 volt phantom powered studio mixers and pre-amps. It provides an optimum voltage for the OKMs, and transformer isolated balanced mic level inputs. The improvement in signal to noise is significant when compared to the A3 (<8dB). Headroom is also slightly improved. The unit requires no battery, but uses the mixer/pre-amp's 48V to power the circuitry that provides the bias voltage for the microphones. The mics are isolated from the 48V by two mini audio transformers.