A 4377 • Phase5 Public Address Mixer Amplifier 125W 4 Input

This model was created for installations requiring the power of the Phase5 amplifier with fewer 'bells and whistles'. It still offers three mic and four auxiliary inputs, alert/evac option, phantom powering, VOX muting and 24V DC power option. 125W RMS power output is ideal for powering long strings of 100V line speakers in larger installations such as shopping centres.

SKU: A 4377 Categories: , , ,
Designed for applications requiring up to three microphone inputs, without compromising output power and overall performance. Each model features three inputs which can be configured for either microphone or line level operation.  A 4377 and A 4387 conservatively deliver 125W and 250W RMS power respectively. Frequency response extends from 50Hz to 12kHz ±3dB at a total harmonic distortion (THD) of less than 0.5% @ 1kHz. Adjustable vox muting is provided on inputs one and two, which, when activated, automatically mutes the other inputs. 

Bass/treble controls and phantom powering capability enable unparallelled flexibility for a wide scope of applications such as factories, workshops, mine sites, sports clubs and office buildings.  

Both operate from 240V AC mains or 24V DC permitting battery backup operation during mains power failure. Output is 100V line 70V line or low impedance operation is available with internal configuration. Thermal, over current & over load protection circuitry and fuses on both AC and DC provide excellent fault condition protection and robust performance. Tape output sockets are provided for recording purposes or feeding into additional power amplifiers.

A 4573 Alert/evac option board: When fitted, generates pre chime, bell, alert and evacuation tones.  The alert tone can function continuously, or switch to evac tone after a preset time delay (adjustable 30 seconds to 4.5 minutes).  Simply connects to the  amplifier internally via the cable provided.

A 4373 Digital remote volume option board: When fitted and used in conjunction with A 2280B wallplate to provide remote volume level adjustment. Ideal for situations where the amplifier is located in a remote rack. 

Key Features:

  • Multi-stage thermally cued fan cooling
  • 2U 19” rack mount (with optional A 4376)
  • Tape record out terminals
  • Optional alert, evac/chime tone generator (A 4573)
  • 3 mic input and 4 auxiliary inputs
  • Phantom powering available on all inputs
  • Adjustable vox muting on inputs 1 & 2.
  • Bass and treble tone controls
  • Terminals for 100V line output
  • 240V AC or 24V DC power operation
  • Thermal & fuse overload protection
  • Built in short circuit protection
  • Australian designed & assembled


Developed, designed & assembled in Australia.
Since 1976 Redback PA products have been manufactured in Perth, Western Australia by Altronics. With over 40 years experience in the commercial audio industry, we offer consultants, installers and end users reliable products of high build quality with local product support.

Backed by an industry leading 10 Year Manufacturer Warranty.
Our Redback products have a long tried and tested history of bulletproof reliability. Altronics offers a 10 Year Warranty on all Australian Made Redback products. Our local in-house service department has all the know how to answer technical queries and provide timely service.

Power Outputs
Power: 125 watts RMS
Distortion: < 0.5%, @ 1kHz
Output line: 100V

Frequency Response
Mic inputs : 50Hz – 12kHz, -3dB
Line inputs: 50Hz – 15kHz, -3dB

Mic Sensitivity
Mic inputs: 3mV
Line inputs: 1V
Music input: 500mV

Signal to Noise Ratio
Mic inputs: > 75dB below rated output
Line Output: 600Ω balanced, 0dB , 3 Pin XLR

Output Connectors
Speakers: Screw terminals

Input Connectors
Inputs: 3 pin XLR balanced or 2 x RCA
24V DC power: Screw terminals
240V AC power: IEC power connector
Muting: PTT via microphone switch contacts, VOX muting (inputs 1-2)

Mic/Line/Music inputs: Volume
Power: On/off switch
Indicators: Power, signal present, output peak limiting, overtemp ,Overload Protect, Half Power, 24V DC

Power Supply: 240V AC or 24V DC
Fuse Protection: 125W – 5A AC ,10A DC, 250W – 7.5A AC ,20A DC

Dimensions: 483W x 300D x 88H

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