The PPM Driver Card can accept balanced or unbalanced input signals (with automatic gain sensing), and provides a number of outputs. Sum, difference (with switchable 20dB gain), left, right and mono signals are internally produced and can be switched to the PPM drivers and outputs by means of front-panel switches. The tri-colour LED stereo phase indicator is standard, giving a clear signal phase indication from tone, and good indication even on programme audio. True mono audio with VCA control is fed via the loudspeaker amplifier to the internal loudspeaker whilst stereo audio is available for headphone monitoring from the headphone driver amplifier.