The HD-RA35U is a four input audio mixer amplifier for systems demanding the broadest range of features and the highest energy efficiency. Two output power amplifier zones, 35W (Zone 1) and 4W (Zone 2), are driven from high-efficiency Class D amplifier stages. The mixer and amplifier sections all normally shut down (standby "sleep" mode) when audio is absent and automatically turn on when needed. A paging source is normally connected to Input 1. The Zone 1 amplifier output level for inputs 2, 3 and 4 is VCA controlled using various optional RDL remote controls. This allows the user controls to be conveniently wall mounted without running audio to and from the remote control location. The Zone 1 output drives 4 ohm or 8 ohm speakers. The output impedance is switch-selectable on the rear panel. The Zone 2 amplifier output drives an 8 ohm speaker and/or 600 ohms telephone equipment.