A 4255A • Compact 1RU Public Address Mixer Amplifier 100W

This compact 1RU rack mount amplifier outputs 100W RMS for 100V line systems. It is suitable for both stand alone PA system use, or as a zone amplifier in a larger system requiring local inputs. Operates on 240V AC or 24V DC for battery backup operation.

SKU: A 4255A Categories: ,

These compact 1RU rack mount amplifiers are suitable for both stand alone PA system use, or as zone amplifiers in larger systems requiring local inputs. All models operate on 240V ac or 24V dc for battery backup operation. All models include a choice of six source options on 2 inputs. Input one consists of a 3-pin XLR which can be set for either balanced mic level (3mV) or balanced line level (2V), adjusted via a rear mounted trimpot. A dual RCA is also provided on input one with adjustable sensitivity of either 300mV or 1V. Input two consists of three sets of dual RCA sockets on the rear panel and a 3.5mm jack on the front panel. Auxiliary source inputs are selected via the front panel switch. Input one can be DIP switch selectable to VOX mute input two.

Phantom power is also provided on input one XLR. Volume level controls are provided on the front panel for inputs one and two. The circuit includes protection features in case of output over voltage, over current and over temperature. All are self re-setting once the fault condition is removed. Visual indication via front panel LEDs display amplifier status at all times.

Key Features:

  • Compact 1RU 19” rack mount design
  • Balanced mic or line input
  • VOX muting
  • Phantom power
  • Four auxiliary inputs
  • 3.5mm Jack Input (Front Mounted)
  • Overload limiting
  • Over voltage limiting
  • On demand fan cooling
  • Over temperature shut down protection
  • Dual input connectors
  • Variable input sensitivities
  • 240V AC / 24V DC operation
  • Australian designed & manufactured


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 output: 100 watts RMS
Distortion: < 0.5%, @ 1kHz

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

Mic input: 3mV-2V balanced
Line input: 300mV-1V
Aux inputs: 300mV – 1V
3.5mm input: 600mV

Signal to noise ratio
Mic input: > 75dB below rated output
Line input: > 81dB below rated output

Output Connectors
Speakers: Screw terminals

Input Connectors
Inputs 1: 3 pin XLR balanced or 2 x RCA
Input 2: 3 x RCA and 3.5mm Jack
24V DC power: Screw terminals
240V AC power: IEC power connector

Size & Weight
Dimensions: ≈ 483W x 210D x 44H
Weight: ≈ 6kg

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