The HD-RA35UA 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, 35 watts (Zone 1) and 4 watts (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 provides a constant voltage output (25 V, 70 V or 100 V). The Zone 2 amplifier output drives an 8 ohm speaker and/or 600 ohm telephone equipment. The HD-RA35UA is engineered, tested and manufactured in the U.S.A. to strict energy conservation standards. The unit consumes less than 1W of mains power in standby mode, and meets power amplifier efficiency specifications with analog-filtered Class-D digital output stages for both power amplifier output zones and for the 600 ohm output. The HD-RA35UA features two mixers. The Zone 1 mixer is split between the front-panel (Paging Input 1 and tone controls) and a remote control (Inputs 2, 3 and 4) providing user level controls for the 35 watt amplifier output. The tone controls adjust the equalization at the Zone 1 amplifier output and can be switch selected on the rear panel to also adjust the equalization at the line-level output. The Zone 2 mixer on the rear panel provides level trimmers normally set by the installer to provide music-on-hold and/or for background music in a small zone equipped with an 8 ohm speaker. The Zone 2 section includes a 4 watt amplifier, a 600 ohm transformer-balanced MOH output, and an active balanced line-level output that may be used to feed another audio power amplifier.