Redback A 4020B User manual

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Redback® A 4020B 30W PA Amplier
User manual revision number: 1.0 29/04/2022
Operating Manual
A 4020B 30 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.
Distributed by Altronic Distributors Pty. Ltd.
Phone: [phone] Fax: [phone] Internet: www.altronics.com.au

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Redback® A 4020B 30W PA Amplier
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
© 2022 Altronic Distributors

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Redback® A 4020B 30W PA Amplier
OVERVIEW
The amplier features one balanced microphone and two line level (RCA) inputs. VOX muting is included which mutes in-
put 2 when the input 1 microphone or line input is activated. The A 4020B conservatively delivers 30W RMS power with a
frequency response extending from ≈ 50Hz to 10kHz ±3dB at a total harmonic distortion (THD) of less than 0.5% @ 1kHz.
Bass and treble controls and VOX sensitivity are all adjustable.
The amplier operates from 240V AC mains and the output comes standard suitable for a 100V line load.
Thermal overload, over current and overload protection circuitry, and fuses on both AC and the output speaker line pro-
vide excellent fault condition protection and robust performance.
FEATURES
• 1 Balanced microphone input
• 2 Line inputs
• VOX muting on input 1
• Adjustable VOX level sensitivity
• Bass and Treble controls
• Full 30W RMS output (100V)
• 100V output
• Thermal Overload protected
• Over voltage protection
• Over current protection
• Short circuit protection
• Very Low noise and distortion
• 240V AC operation
INPUT CONNECTIONS
The microphone input can be connected via a balanced XLR 3 pin
socket. Refer to gure 1.
The line inputs are connected via standard RCA sockets.
Fig 1
SPEAKER CONNECTIONS
Speakers fitted with 100V line transformers may be connected to the output terminals on the rear of the amplifier. Always
ensure the total load of the fitted speakers does not exceed the rated output of the amplifier (ie 30 watts for the A 4020B
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 such as Altronics Q 2004 is required. Fig 2 lists the imped-
ance at certain loads of speakers fitted with 70V and 100V line transformers. So for a total load of 30 watts using 100V
line transformer fitted speakers, the impedance of the speaker load should be 333Ω.
Fig 2
VOX MUTING
VOX muting is provided on input one, which, when activated, automatically mutes input 2. VOX can be selected ON or
OFF via the internal jumper labelled (Mute). This is factory set in the OFF position. VOX sensitivity is adjusted via the trim-
pot on the rear of the unit.
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 fitted
with line-matching transformers. This is to overcome the effects of connecting
speakers in parallel and cable losses. The amplifier generally has an output
voltage of 100 volts (70 volts is typically used in North America, however
operation is similar). In this configuration the total wattage load on the amplifier
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 amplifier.
Measuring 70/100V Line Speaker Impedance: To measure amplifier 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.
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
Redback Q 2004
From Microphone
Input
Unbalanced
1
2
3
Signal
Shield
XLR Mic
Input
From Microphone
Input
Balanced
Shield
XLR Mic
Input
Signal
12
3
Microphone Connections
Connector Type:..................XLR 3Pin Female
Pin 1: .....................................................Earth
Pin 2: ...............................Signal Inphase (hot)
Pin 3: ......................Signal Out of Phase (cold)
Figure 1.

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Redback® A 4020B 30W PA Amplier
OPERATION
Once all inputs and the output is connected:
1) Turn the bass and treble controls to midway.
2) Turn the volume controls to zero.
3) Turn the power switch on. The power indicator should illuminate.
4) Turn on microphone or auxiliary input source and adjust appropriate volume control to desired level.
Note: Both the mic and auxiliary for input 1 are mixed together. Both the mic and auxiliary input can be run together but
note there is only the one volume control for both of these.
TROUBLESHOOTING
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 fuse. Replace
with only the correct type and rating (800mA M205). 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.
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 4020B - 30 Watts RMS
Distortion:..................................................< 0.5%, @ 1kHz
Output line: ............................................................... 100V
FREQUENCY RESPONSE
Mic input :............................................52Hz - 10kHz, ±3dB
Line inputs: ..........................................40Hz - 10kHz, ±3dB
INPUT SENSITIVITY
Mic inputs: ................................................ 2.6mV balanced
Line inputs:...............................................................150mV
SIGNAL
All volume controls min, typically 72dB below rated output.
All inputs display same S/N ratio
LINE OUTPUT .................. 600Ω balanced, 0dB , 3 Pin XLR
OUTPUT CONNECTORS
Speakers: .................................................. Screw terminals
INPUT CONNECTORS
Mic Input: ............................................ 3 pin XLR balanced
Line inputs: .................... RCA stereo socket, bridged mono
240V AC power: ............................... IEC power connector
MUTING:.......................................... VOX muting (input 2)
CONTROLS
Mic/Line inputs: ...................................................... Volume
Power: .......................................................... On/off switch
Indicators: ................................................................ Power
Bass: ......................................................... ±10dB @ 100Hz
Treble: ....................................................... ±13dB @ 10kHz
POWER SUPPLY: ................................................. 240V AC
FUSE PROTECTION: ........................................ 800mA AC
........................... 3A x 2 (DC internal)
DIMENSIONS .................................. ≈300W x 220D x 74H