Radio Design Labs HD-MA35
35 Watt Mixer Amplifier

OUR PART #  HD-MA35


The Radio Design Labs HD-MA35 is a three input audio mixer amplifier for systems demanding a broad range of features and high energy efficiency. Two output power amplifier zones are provided, 35 W (Zone 1) and 2 W (Zone 2). The Zone 1 output is driven from a high-efficiency Class D amplifier stage. 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 10 kO controls. This output drives 4 O or 8 O speakers. The output impedance is switch-selectable on the rear panel. The Zone 2 amplifier output drives an 8 O speaker and/or 600 O telephone equipment. The HD-MA35A has all the features of the HD-MA35 except its 35 W (Zone 1) amplifier provides a constant voltage output (25 V, 70 V or 100 V) instead of a low impedance speaker output. The HD-MA35 is engineered and manufactured in the U.S.A.

The HD-MA35 features two mixers. The Zone 1 mixer is located on the front-panel providing user level and tone controls for the 35 W amplifier output. The tone controls adjust the equalization at the Zone 1 amplifier 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 O speaker. The Zone 2 section includes a 2 W amplifier and a 600 O transformer-balanced MOH output.

The HD-MA35 has three inputs that are common to both mixers. Input 1 accepts a balanced mic or line level source. Inputs 2 and 3 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 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 and/or 3 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.
  • Inputs 2 and 3 each provide unbalanced stereo RCA input jacks, summed to mono.

The HD-MA35 is equipped with a master VCA for remote adjustment of the Zone 1 amplifier output. A detachable terminal block is provided for direct connection of an optional RDL remote level control.

A balanced line-level output is provided on a detachable terminal block to feed the inputs of other audio equipment or power amplifiers. Ground-referenced 24 Vdc power is available on a rear-panel terminal block to power an optional external RDL module which may be mounted on the panel space provided. External module type examples: audio filtering or processing, mixing, isolation, twisted-pair sender/receiver.

The Zone 1 amplifier includes an analog compressor/limiter for audio fidelity noticeably superior to conventional class D amplifiers with digital limiting. Increasing the input gain can substantially increase the average output power beyond that of a standard 35 W amplifier. A red front-panel LED flashes when the compressor is preventing output clipping. Normal audio level signals remain unaffected by the compressor thereby preserving audio dynamics. The audio is compressed according to three dynamic time constants providing aural transparency while maintaining clean, unclipped amplified audio for input overloads of up to 20 dB. The HD-MA35, with compression, is capable of producing average audio output levels and clarity normally expected from amplifiers with a much higher output power rating.

A blue POWER LED illuminates when the HD-MA35 is powered from its external 24 Vdc power supply (included). The power LED is dim when the mixer amplifier is in the standby mode, and is bright when the amplifiers are fully active. A front-panel pushbutton is provided to manually switch between standby and active modes. The power amplifiers are equipped with both thermal and output short-circuit protection. The high-efficiency Class D output stage produces minimal heat for all levels of expected voice or music modulation.

RDL HD-MA35 Features:

  • Three inputs with individual front-panel volume controls
  • Bass and Treble tone controls
  • Designed for background music with paging and music-on-hold
  • Master volume VCA controlled with remote adjustment capability
  • Manual or automatic (VOX) priority ducking
  • Balanced inputs and amplified outputs on detachable terminal blocks
  • Unbalanced inputs and outputs on RCA jacks
  • Includes power supply
  • High-efficiency Class D operation

RDL HD-MA35 Specifictions:

  • Amplifier Zones (2):
    • Zone 1 (Main): 35 W RMS, front-panel mixer (user controls)
    • Zone 2: 2 W RMS (8 Ohms), rear-panel mixer (trimmers)
  • Audio Inputs (3): Balanced, mic or line switch selectable on terminal block; 2, unbalanced stereo summing inputs on RCA jacks
  • Maximum Input Level:
    • Mic Input: -11.5 dBu
    • Balanced line input: + 19 dBu
    • Unbalanced Inputs: + 9 dBV (+15.5 dBV, one input) (for 1% THD+N at output)
  • Phantom Voltage: 24 Vdc (IEC 61938: 2013), switch-selectable for the mic input
  • Ducking/Muting Actuation: Automatic (Input 1 VOX: rear-panel adjustable signal threshold with LED indicator) or Manual (contact closure to ground)
  • Ducking/Muting Release Delay: 4 seconds, nominal
  • Ducking/Muting: Switch-selectable for inputs 2 and/or 3, 25 dB ducking attenuation, nominal
  • External RDL Module Power Output: 24 Vdc, 100 mA maximum, ground-referenced
  • Input level:
    • (to cross compressor threshold equaling 23 W amplified output)
    • Mic Input: -50 dBu (2.5 mV), (front panel gain at max.)
    • Balanced line input: -21 dBu (70 mV), (front panel gain at max.)
    • Unbalanced Inputs: -15 dBV (180 mV, front panel gain at max., both inputs driven)
  • Noise (line output):
    • Mic input: -68 dB
    • Balanced line input: -72 dB (below compressor threshold at max gain)
    • Unbalanced Inputs: <-85 dB (max gain)
  • Noise (amplified outputs):
    • Mic input: -68 dB
    • Balanced line input: -72 dB (below compressor threshold at max gain)
    • Unbalanced Inputs: <-75 dB (max gain)
  • THD+N: < 0.5% (1 kHz at compressor threshold, main amp output); < 0.25% (line output, main)
  • CMRR: 
    • Mic input: > 50 dB (50 Hz to 120 Hz)
    • Balanced line input: > 80 dB (50 Hz to 120 Hz, transformer-coupled input)
  • Compressor: Threshold 2 dB below rated output, automatically adjusting attack and release times
  • Frequency Response (mixer):
    • Mic to line output: ±1.5 dB (40 Hz to 25 kHz)
    • Balanced line input to line output: ±1 dB (20 Hz to 20 kHz)
    • Unbalanced line input to line output: ±0.5 dB (20 Hz to 20 kHz)
  • Frequency Response (Zone 1 amplifier): ±1 dB (50 Hz to 20 kHz)
  • Frequency Response (Zone 2 amplifier): 
    • 8 Ohm: ±1.5 dB (50 Hz to 20 kHz)
    • 600 Ohm: ±1.5 dB (30 Hz to 18 kHz)
  • Tone Controls: ±10 dB @ 10 kHz, ±9 dB @ 100 Hz (front-panel) with center detent
  • Audio Outputs (2): 
    • +4 dBu nominal (1.23 V), balanced, terminal block (FLAT)
    • 0 dBu nominal balanced, terminal block (zone 2 mixer, 600 Ohm output)
  • MOH Output: 0 dBu nominal (775 mV), 600 Ohm transformer-isolated, >16 dB headroom
  • Power Amplifier Outputs (2):
    • Zone 1 (main, <1% THD+N): 35 W RMS (4 Ohms), 32 W (8 Ohms) on detachable terminal block (switch-selectable 4 or 8 Ohm impedance)
    • Zone 2: 2 W (8 Ohms, on detachable terminal block)
  • Indicators (6):
    • Front-panel: Signal present (3; 1 per input, green), Compressor activity (red), Power (bright=on, dim=standby, blue)
    • Rear-panel: Ducking/muting threshold (yellow)
  • VCA: Zone 1 (main) master level, 0 to 10 Vdc control, detachable terminal block (compatible with RDL VCA wall controls)
  • Front-panel controls (6): Zone 1 (main) mixer level controls (3, inputs 1 through 3), EQ (2, bass and treble), Power (latching pushbutton, on/standby)
  • Rear-panel controls (9): Mic/Line switch (Input 1), Input 1 ducking/muting detector sensitivity trimmer, Phantom voltage switch (Input 1), Ducking control switches (2, to duck inputs 2 and/or 3), Zone 2 mixer level controls (3, inputs 1 through 3), HD-MA35: Output impedance switch 4 or 8 Ohms
  • Ambient Operating Environment: 0° C to 50° C Maximum; 20° C Recommended
  • Power Supply (included): 100 to 240 Vac, 50-60 Hz, 50 W; 24 Vdc output to amplifier chassis
  • Dimensions (HxWxD): 3.5" x 8.5" x 6.75" (8.89 x 21.6 x 17.1 cm)
  • Weight: 4.5 lb.(2 kg)
  • Package Type: Cardboard Box
  • Package Dimensions: 10.75" x 9.125" x 3.9375"
  • Shipping Weight: 5.08 lbs.
  • WEEE weight: 3.98 lbs.
  • Tariff code: 8518.50.0000
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