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b'Radio Design Labs HD-MA35U/A 35 W Mixer Amplifier
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The HD-MA35UA 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. The Zone 1 amplifier output level may be VCA controlled using various optional RDL remote controls, or by industry standard 0 to 10 Vdc or 0 to 10k ohm controls. This 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-MA35UA is engineered, tested and manufactured in the U.S.A. to strict energy conservation standards. The unit consumes less than 1 watt 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-MA35UA features two mixers. The Zone 1 mixer is located on the front-panel providing user level and tone 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.

The HD-MA35UA has four inputs that are common to both mixers. Inputs 1 and 2 accept balanced mic or line level sources. Inputs 3 and 4 accept unbalanced mono or stereo line-level sources.

Input 1 is switch-selectable MIC or LINE. Phantom voltage (IEC standard 24 Vdc) is switch-selectable for the microphone input. The line input is transformer isolated and accepts balanced or unbalanced, high or low impedance audio sources. A gain trimmer is provided to set the input preamplifier to the optimum gain for the installation.\\n
A paging source is normally connected to Input 1. This input is equipped with push-to-talk terminals and with an adjustable threshold VOX circuit with LED threshold indicator, either (or both) of which may be set to duck ("fade down" or "mute") inputs 2, 3 and/or 4 by 25 dB when a paging signal is active on Input 1. The attenuated inputs fade up to normal volume when the paging message is finished. A rear-panel trimmer allows the start of the fade-up to be delayed from 2 to 6 seconds.\\n
Input 2 is switch-selectable MIC or LINE. Phantom voltage (IEC standard 24 Vdc) is switch-selectable for the microphone input. The line input is active balanced and accepts balanced or unbalanced, high or low impedance sources. A gain trimmer is provided to set the input preamplifier to the optimum gain for the installation.\\n
An RDL Dual-LED VU meter is provided on the rear panel to indicate proper gain adjustment for Inputs 1 and 2. Correct input gain adjustment insures adequate mixer stage headroom.\\n
Inputs 3 and 4 each provide unbalanced stereo RCA input jacks, summed to mono.\\n
The presence of a signal on any of the inputs causes the HD-MA35UA to fully turn on, activating both Zone 1 and 2 power amplifiers and all associated mixing, equalization and compressor circuitry. When input signals are absent, a delay timer is initiated. Rear-panel DIP switches are provided to set the power-down delay timer to a value between 10 minutes and 2 hours in 10 minute increments. After the time-out period, the HD-MA35UA enters the sleep mode until an input signal is received. The switches may be set to disable the sleep mode for systems specifying continuous amplifier operation...