Redback A 4377A User manual

www.redbackaudio.com.au Redback® Proudly Made In Australia 1
Redback® 125/250Watt Mixer Ampliers
User manual revision number: 1.2 05/05/2023
Operating Manual
A 4377A 125 WATT PUBLIC ADDRESS AMPLIFIER
A 4387A 250 WATT PUBLIC ADDRESS AMPLIFIER
IMPORTANT NOTE:
Please read these instructions carefully from front to back prior to installation.
They include important setup instructions.
Failure to follow these instructions may prevent the unit from working as designed.
Redback® Proudly Made In Australia
Distributed by Altronic Distributors Pty. Ltd.
Phone: [phone] Fax: [phone] Internet: www.altronics.com.au
Optional Extras
A 2280B
Remote Volume Wall Plate
A 4573
Alert/Evacuation Module
A 4373
Remote Volume Module
A 4376
Rack Mount Ears

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Redback® 125/250Watt Mixer Ampliers
REDBACK is a registered trademark of Altronic Distributors Pty Ltd
You may be surprised to learn that Altronics is still manufacturing hundreds of product lines right here in Australia. We
have resisted the move offshore by offering our customers better quality products with innovations to save them time and
money.
Our Balcatta production facility manufactures/assembles:
Redback public address products
One-shot speaker & grill combinations
Zip-Rack 19 inch rack frame products
We strive to support local suppliers wherever possible in our supply chain, helping to support Australia’s manufacturing
industry.
Redback Audio Products
100% developed, designed & assembled in Australia.
Since 1976 we have been manufacturing Redback ampliers in Perth, Western Australia. 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. We believe there is signicant added value for customers when purchasing an Australian made
Redback amplier or PA product.
Local support & feedback.
Our best product features come as a direct result of feedback from our customers, and when you call us, you speak to a
real person - no recorded messages, call centres or automated push button options.
It’s not only the assembly team at Altronics who are employed as a direct result of your purchase, but hundreds more at
local companies used in the supply chain.
Industry leading 10 year warranty.
There’s a reason we have the industry leading DECADE warranty. It’s because of a long tried and tested history of bullet-
proof reliability. We’ve heard PA contractors tell us they still see the original Redford amplier still in service in schools.
We offer this comprehensive parts & labour warranty on almost every Australian Made Redback public address product.
This offers both installers and end users peace of mind that they will receive prompt local servicing in the rare event of any
problems.
Published by Altronic Distributors
© 2021 Altronic Distributors

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Redback® 125/250Watt Mixer Ampliers
OVERVIEW
The Redback A 4377A 125 Watt and A 4387A 250 Watt 4 channel mixer ampliers are specically designed for applica-
tions requiring up to three microphone inputs, without compromising output power and overall performance. The ampli-
ers feature three inputs which can be congured for either microphone or line level operation.
The A 4377A conservatively delivers 125W RMS power, while the A 4387A delivers 250W RMS. Frequency response ex-
tends from 50Hz to 15kHz ±3dB at a total harmonic distortion (THD) of less than 0.5% @ 1kHz.
Vox muting is provided on inputs one and two, which, when activated, automatically mutes the other inputs. Bass and
treble controls and phantom powering capability enable unparalleled exibility for a wide scope of applications such as
factories, workshops, mine sites, sports clubs and ofce buildings.
The ampliers operate from 240V AC mains or 24V DC permitting battery backup operation during mains power failure.
The output comes standard suitable for a 100V line load, but this can be congured internally to 70V line or low imped-
ance (4 - 16Ω) loads. (Check the Website for details).
Thermal overload, overcurrent and overload protection circuitry and fuses on both AC and DC provide excellent fault
condition protection and robust performance. The amplier also utilises a half power mode which enables the amplier to
continue to run at a reduced output level if it is being over driven.
Tape output sockets are provided for recording purposes or feeding into additional power ampliers.
Remote volume available when A 4373 Digital volume control module tted internally and external A 2280B wall plate or
1KΩ potentiometer connected.
Alert and Evacuation tones (conforming to AS1607.4) along with chime tones and voice over message option available
when optional A 4573 tted.
FEATURES
• 3 Balanced microphone inputs / 3 Aux inputs / 1 Music input
• Robust design incorporating latest Mosfet technology
• Very Low noise and distortion
• 100V standard with optional 70V and 4-16Ω outputs
• 240V AC or 24V DC operation
• VOX muting on inputs 1 and 2 (Switch selectable internally)
• Adjustable VOX level sensitivities
• Bass and Treble controls
• Tape Output
• Phantom power on microphone inputs (DIP switch selectable internally)
• Multi stage thermally cued fan cooling
• Output Peak Limited
• Thermal Overload protected
• Signal Presence Indicator
• Half power mode when overdriven
• Fault Indicators
• 24V DC Power Status Indicator
• Optional Alert/Evac module with voice over message for emergency tones (A 4573)
• Optional remote volume (With A 4373 Digital volume control module tted and external A 2280B wall plate)
• Rack Mountable (suits 19 inch racks) with optional A 4376 rack ears

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Redback® 125/250Watt Mixer Ampliers
Figure 1 shows the layout of the front panel.
Fig 1
1 Inputs 1-4 volume controls
Use these controls to adjust the output volume of inputs 1-4 (volume 3 is used to adjust the volume of input 4 the
music input.
2 Master volume Control
Use this control to adjust the master volume.
3 Bass and Treble Controls
Use these controls to adjust the bass and treble.
4 OverTemp/ Half Power Indicator
When this LED is red it indicates when the amplier is overheating. The output will be disconnected until the
amplier is once again cool enough to operate. If thie LED is orange the amplier has gone into half power mode.
This mode lets the amplier continue to run at a lower output rather than shutdown completely. This mode might
be initiated from the amplier being overdriven or overloaded.
5 Power Switch
Use this to turn the unit on.
6 On Indicator
This led indicates the unit has power.
7 24V DC Indicator
This LED indicates when the amplier is being powered from the 24V input.
8 Fault Indicator
This led indicates when the amplier has a fault.
9 Peak Limit Indicator
This LED indicates when the input signal is clipping.
10 OverLoad Indicator
This LED indicates when the output is drawing too much current from the amplier. The output will be
disconnected until the current draw is reduced.
11 Protect Indicator
This LED indicates when the amplier module has an internal circuitry fault.
12 Signal Presence Indicator
This LED indicates when an input signal is present.
13 Music Input
Use this input to connect a portable music player. This input over-rides the rear input 3 and is adjusted via the
volume 3 pot.
14 Vox level controls
Use these controls to adjust the vox sensitivities of inputs 1-2.
Model : A 4387
250W Public Address Amplier
24V
Signal Protect
DC
Over
Load
Power
Local Music
Input
Treble
Bass
On
Master Volume
Volume 1 Volume 2 Volume 3
_
0
+
Present
VOX 1
Sens.
VOX 2
Sens.
Fault
Limit
Over Temp
Half Power
Peak
14
1 2 3 4 5
678910111213
0
2
46
8
10 0
2
46
8
10 0
2
46
8
10 0
2
46
8
10
_
0
+

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Redback® 125/250Watt Mixer Ampliers
Figure 2 shows the layout of the rear panel.
Fig 2
1 240V AC power socket (Australian standard)
Connects to 240V AC mains power with the included IEC lead. The internal fuse is an M205 5Amp for the
A 4377A 125 Watt amplier and an M205 7.5Amp for the A 4387A 250 Watt amplier.
2 Output Connections
Speakers tted with a 100V line transformer may be connected to these terminals. Always ensure that the total
load of the speakers does not exceed the rated output of the amplier i.e. 80Ω minimum at 100V for 125W
and 40Ω minimum at 100V for 250 Watts. Otherwise either the DC or mains fuse could blow or the fault led
activate and the amp will shut down. Always be careful to avoid short circuits and connection to the wrong
terminals.
3 Optional Alert/Evacuation Tone Generator with Voice Over Message
When tted this card provides standard Alert and Evacuation tones which conform to AS1607.4. A voice over
message can be recorded to the card and various chime tones are included.
4 Inputs 1-3
These inputs can be either a balanced XLR input with sensitivities of 500mV or dual RCA line inputs with a 1V
input sensitivity. The line input dual RCA connectors are internally mixed to produce a mono input signal.
5 Tape Out
Dual RCA’s provided for recording purposes. This is a line level output.
6 Optional Plugin
This connection is to be used when the optional A 4373 Digital Volume Board if tted inside the amplifer. This
provides remote volume when used in conjunction with a 1K potentiometer wired to these terminals.
7 24VDC IN
Battery Backup: Provision has been provided to run the amplier from a suitably rated 24V battery system in the
event of a mains failure. Using appropriately rated cable, connect the battery to the “24V DC In” terminals.
Observe correct polarity when connecting. (see Fig 5 for more details)
8 DC Resettable fuses
This fuse protect the internal power supply. If the fuse is tripped it is easily reset by pressing the small button on
the fuse.
240V AC @ 50Hz
RISK OF ELECTRIC SHOCK
OPEN BY QUALIFIED
PERSONNEL ONLY !
CAUTION
Tape Out Line 1 Mic 3 Mic 2 Mic 1
12
3
1 • Shield
2 • Hot
3 • Cold
MIc XLR
wiring
Conguration
Line 2
Line 3
L
R
L
R
L
R
Output
125W
Fuse
5 Amp
7.5 Amp
250W
AC Fuse (M 205)
DC FuseOutput
125W 10 Amp
20 Amp
250W
Resettable
DC Fuse
100V
OUT L
R
Optional
Plugin
- +
+_
24V
DC IN
Made in Australia by
Altronic Distributors Pty Ltd
www.redbackaudio.com.au
- +
+_
1
45
2
6
7
8
2 1
3
2 1
3
2 1
3

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Redback® 125/250Watt Mixer Ampliers
SPEAKER CONNECTIONS
Speakers fitted with 100V line transformers may be connected to the output terminals on the rear of the amplifer.
Always ensure the total load of the fitted speakers does not exceed the rated output of the amplifier (ie 125 watts for the
A 4377A and 250 watts for the A 4387A amplifier) otherwise damage may result. When fitting speakers with line
transformers the impedance of the load cannot be measured using a standard multimeter. An impedance meter is
required. Fig 3 lists the impedance at certain loads of speakers fitted with 70V and 100V line transformers. So for a total
load of 125 watts using 100V line transformer fitted speakers, the impedance of the speaker load should be 80Ω.
Fig 3
AUDIO CONNECTIONS
The amplier has three balanced XLR audio inputs, three dual RCA line inputs which are internally mixed
to create mono signals and a front mounted Music Input for portable devices. This input when connect-
ed, over-rides the rear channel 3 audio sources and is adjusted via the volume 3 level control.
A VOX function is also included which when enabled will allow input 1 to mute inputs 2 and 3, or input
2 to mute input 3. The VOX circuitry is selected by internal switches as shown in gure 5. The VOX1
switch when set to ON will allow input 1 to mute inputs 2 & 3. The VOX2 switch when set to ON will
allow input 2 to mute input 3. The VOX sensitivity is adjusted by the trimpots located on the front of the
amplier.
Fig 4 shows a typical install where the A 4377A has a balanced microphone connected to input 1 and a
Line level source connected to input 2. If the VOX1 switch is set to “ON”, the microphone will VOX mute
the CD player connected to input 2.
Fig 4
i
Wiring speakers in parallel for 70/100V line: Where several speakers are to
be used at one time, on one circuit, it becomes necessary to use speakers tted
with line-matching transformers. This is to overcome the effects of connecting
speakers in parallel and cable losses. The amplier generally has an output
voltage of 100 volts (70 volts is typically used in North America, however
operation is similar). In this conguration the total wattage load on the amplier
is derived from adding all the line transformer primary tap ratings together. For
example, 70 one watt speakers will have a total speaker load of 70 watts. Or
alternatively, it is conceivable to connect 100 one watt speakers to a 100 watt,
100 volt line amplier.
Measuring 70/100V Line Speaker Impedance: To measure amplier system
load, you must use an impedance meter in order to measure the ac resistance
of the connected speaker network. Impedance cannot be measured with a
standard multimeter, as this measures the dc resistance. Use the Altronics
Q 2001 or similar impedance meter.
About 70V & 100V Line Speaker Systems
Load 70V 100V
0.5W 9.4kΩ 20kΩ
0.66W 7.12kΩ 15kΩ
1W 4.7kΩ 10kΩ
1.25W 3.76kΩ 8kΩ
2W 2.35kΩ 5kΩ
2.5W 1.88kΩ 4kΩ
3W 1.56kΩ 3.3kΩ
5W 940Ω 2kΩ
7.5W 626Ω 1.3kΩ
10W 470Ω 1kΩ
15W 313Ω 666Ω
20W 235Ω 500Ω
30W 156Ω 333Ω
40W 117Ω 250Ω
60W 78Ω 166Ω
100W 47Ω 100Ω
125W 37Ω 80Ω
250W 19Ω 40Ω
500W 9.4Ω 20Ω
240V AC @ 50Hz
RISK OF ELECTRIC SHOCK
OPEN BY QUALIFIED
PERSONNEL ONLY !
CAUTION
Tape Out Line 1 Mic 3 Mic 2 Mic 1
12
3
1 • Shield
2 • Hot
3 • Cold
MIc XLR
wiring
Conguration
Line 2
Line 3
L
R
L
R
L
R
Output
125W
Fuse
5 Amp
7.5 Amp
250W
AC Fuse (M 205)
DC FuseOutput
125W 10 Amp
20 Amp
250W
Resettable
DC Fuse
Voice Chime Alert
Over & Evac
EV
COM
CAN
CH
AL
100V
OUT L
R
Optional
Plugin
- +
+_
24V
DC IN
Made in Australia by
Altronic Distributors Pty Ltd
www.redbackaudio.com.au
- +
+_
Speakers tted with
100V line transformers.
CD
REDBACK
2 1
3
2 1
3
2 1
3
12
3
1 • Earth/Shield
2 • Signal Hot
3 • Signal Cold
MIc XLR
wiring
Conguration

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Redback® 125/250Watt Mixer Ampliers
PHANTOM POWER
All three microphone inputs have DIP switch selectable phantom power. When enabled 15V DC will be connected to the
Hot and Cold pins of the corresponding XLR. To access the DIP switches, rst disconnect power from the unit and then
remove the lid. The location of the DIP switches is shown in gure 5.
The Phantom power DIP switch settings are:
DIP 1 enables the phantom power to the XLR connector on input 1.
DIP 2 enables the phantom power to the XLR connector on input 2.
DIP 3 enables the phantom power to the XLR connector on input 3.
DIP 4 is not used.
VOX MUTING
Vox muting is provided on inputs one and two, which, when activated, automatically mutes the other inputs.
The VOX1 switch when set to ON will allow input 1 to mute inputs 2 & 3. The VOX2 switch when set to ON will allow
input 2 to mute input 3.
The VOX sensitivity is adjusted by the trimpots located on the front of the amplier (see gure 1).
REMOTE VOLUME (Optional)
It is possible to control the master volume with the addition of the A 4373 Digital Remote volume board and a 1kΩ
potentiometer (or Altronics A 2280B wall plate) tted across the terminals labelled “Optional Plugin” on the rear of the
amplier. The plugin board is tted inside the amplier in the location shown in gure 5.
NOTE: Take special care with the orientation of the board and remove power from the amplier before tting.
Fig 5
PHANTOM POWER
DIP SWITCHES
1=MIC1
2=MIC2
3=MIC3
VOX1 VOX2
ON
OFF
ON
OFF
EARTH
LIFT
SWITCH
EARTH
LIFT
PLUGIN
PLUGIN

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Redback® 125/250Watt Mixer Ampliers
POWER SUPPLY
The amplier operates on 230V AC or primarily for battery backup operation a 24V DC supply. Ensure power is switched
OFF at the front panel before connecting either mains power to the IEC socket or 24V DC to the screw terminal input. As
high currents may be drawn when operating from a 24V DC supply conrm the capacity of the DC power supply used.
TROUBLESHOOTING
If the REDBACK Phase 4 amplier fails to deliver the rated performance, check the following:
No Power, No Lights
Make sure amplier power switch is on. Make sure mains power switch is on at the wall. Check the mains and DC fuse.
Replace with only the correct type and rating. Over rated fuses with invalidate warranty.
Distorted Output
Check that the speaker type is correct for the output that you are using (ie. 100V line). Check for any short circuits on the
speaker line.
Very Low Output Volume
Make sure that the input is the correct level (check for shorted connectors). Check for any short circuits on the speaker
line.
Check if signal LED on the front panel is lit to indicate there is signal. If it is not lit there is no signal present.
Continually Blows Fuses
Make sure that the speaker line is not shorted. Check speaker types, ratings and if on correct output.
Amplier Keeps on Cutting In & Out
Make sure that there is adequate ventilation around the amplier. Check the vent slots on the front,top and sides are not
covered or blocked and the fan on the rear is functioning correctly. Check also speaker types, ratings and for any short
circuits on the speaker line.
* Specications subject to change without notice
All Australian made Redback products are covered by a 10 year warranty.
Should a product become faulty please contact us to obtain a return authorisation number. Please ensure you have all the
relevant documentation on hand. We do not accept unauthorised returns. Proof of purchase is required so please retain
your invoice.
SPECIFICATIONS
POWER OUTPUTS
Power: ........................................A 4377A -125 watts RMS
..................................... A 4387A - 250 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)
CONTROLS
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
WEIGHT: ................................................. A 4377A ≈ 11kg
.............................................. A 4387A ≈ 15.5kg
CURRENT DRAW:
A 4377A ....................................... Min ≈ 300 mA
........................................... Max ≈ 9.6A
A 4387A ....................................... Min ≈ 350 mA
............................................ Max ≈ 20A