$1595.00 per ea

Quantity Price
ea $1,595.00
2+ $1,435.00
per ea
All prices shown are (inc. GST)


Designed in conjunction with Australia’s leading PA professionals to cater for the needs of multi-source installations. This redesigned unit offers the ability to monitor amplifier status via the colour LCD screen, plus custom labelling of inputs. The A 2711 optional USB & SD card module provides music playback when fitted.

Engineered for professional PA installations, the A 4275B and A 4285B conservatively deliver 125W and 250W RMS power respectively. Frequency response extends from 50Hz to 15kHz ±3dB at a total harmonic distortion (THD) of less than 0.5% @ 1kHz. Voice/Vox muting, including three levels of input priority, bass and treble controls and phantom powering capability enable unparalleled flexibility for a wide scope of applications such as schools, shopping centres, workshops, mine sites and office buildings. Operates from 240V ac mains or 24V dc permitting battery backup operation during mains power failure. Output can be 100V line, 70V line or low impedance (4 - 16 Ohm) loads. The circuit includes thermal overload shutdown, over current and overload protection plus fuses on both ac and dc supply rails.

LCD: Indicates input and output levels, amplifier status; including heatsink temperature, overload and over current conditions. 240V ac or 24V dc operation. Also allows custom labelling of input sources via USB keyboard.

Input configuration: Each input can be configured for either balanced microphone or line use. A dip switch is supplied for each input providing the following features: Phantom power on/off, Mic or line, 100mV or 1V, Vox muting on/off (priority)

Three levels of priority: Priority selection is by a dip switch on the rear panel: Input 1 over 2-6, input 2 over 3-6 and input 3 over 4-6.

Overload protection: In the event of an overload, the output current is limited by the internal circuitry, thus reducing the output voltage at the speaker terminals.

Input Limiting: Limits the output to 110V regardless of input level. This prevents dangerously high voltages from damaging the loudspeaker.

A 4573 Alert/evac option board: 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 2280B Remote volume wall plate: Connects via figure 8 cable to the “remote volume” terminals of the amplifier. Enabling overall volume to be adjusted as required. Features a PCB jumper to reverse the volume control direction. Maximum cable length 100m.


  • VU meter on LCD screen
  • Output peak limited
  • Multi-stage thermally cued fan cooling
  • 2U 19" rack mount
  • Tape record out terminals
  • Remote volume facility
  • Optional alert, evac & chime tone generator (A 4573)
  • Vox activated 24V dc output
  • 6 inputs with 3 pin XLR or 2 x RCA sockets
  • Phantom powering available on all inputs
  • Three levels of priority
  • Option for mic/line to operate vox muting on inputs 1 to 3
  • Push to talk (PTT) terminals on rear panel
  • Bass and treble tone controls
  • Power amp line out connector
  • Terminals for 100V line, 70V line and 4 - 16Ω loads
  • 240V ac or 24V dc power operation
  • Thermal & fuse overload protection
  • Built in short circuit protection
  • 300mA trickle charge facility for 24V dc batteries
  • Master volume can be configured as pre or post line out

100% 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. Read more about our Australian Made products

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. Read more about our industry leading warranty.

Information & Downloads


  • Power Outputs
  • 250 watts RMS
  • Distortion: < 0.5%, @ 1kHz
  • Output line: 70V, 100V or 4 - 16Ω
  • Line output: 600 Ohm balanced, 0dBV
  • Frequency Response
  • Mic inputs: 50Hz - 12kHz, -3dB
  • Line inputs: 50Hz - 15kHz, -3dB
  • Sensitivity
  • Mic inputs: 3mV balanced
  • Line inputs: 100mV-1V
  • Signal To Noise Ratio (Limiting by-passed)
  • Mic inputs: > 75dB below rated output
  • Line inputs: > 81dB below rated output
  • Output Connectors
  • Speakers: Screw terminals
  • Line out: 3 pin XLR, Tape out RCA / send & return RCA
  • 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 or VOX muting
  • Controls
  • Mic inputs: Volume
  • Line inputs: Volume
  • Bass: ±10dB @ 100Hz
  • Treble: ±10dB @ 10kHz
  • General
  • Indicators: Power, fault. All other indicators on LCD
  • Power Supply: 240V AC or 24V DC
  • Current Draw: 350mA Standby, 17A Full @ 24V DC
  • Protection: 7.5A DC , 20A DC
  • Dimensions: ≈483W x 330D x 88H
  • Weight: ≈19.5kg
  • Colour: Black
    • *Specifications are subject to change without notice.

Warranty & Returns


We offer 10 years warranty on this product from its date of purchase. This is available from Altronics stores, online purchases or Altronics resellers. In accordance with our full warranty terms we will repair, replace or refund if goods you have purchased from us are defective.


Not withstanding our warranty policy, if you are dissatisfied with our goods or service you may return the goods within 14 days of our despatch date. Simply contact us for a return authorisation number and we will refund your purchase in full, less transport costs on receipt of goods. All returned goods must be in as sold condition including all packaging, instructions, invoices etc.