REDBACK A 4235A PA Mixer Amplifiers User Manual
- June 10, 2024
- redback
Table of Contents
A 4235A PA Mixer Amplifier
Product Information
The Redback A 4235A, A 4245A, and A 4255A are mixer public address amplifiers with power outputs of 30W, 60W, and 100W respectively. The amplifiers have different inputs, including a balanced XLR input, dual RCA line input, and front-mounted 3.5mm jack. The A 4235A/45A/55A range of amplifiers have a set of options that are enabled via the DIP switches 1-8. The amplifiers also have a 100V output to connect to speakers fitted with a 100V line transformer.
Product Usage
- Connect the amplifier to a 220-240V AC @ 50Hz power source using the 240V AC input.
- Connect speakers fitted with a 100V line transformer to the 100V output. Ensure that the total load of the speakers does not exceed the rated output of the amplifier.
- Adjust the input sensitivity for each input as needed using DIP switches 1-6. Input 1 also has adjustable input sensitivity via DIP switch 7.
- Select the desired input using the rotary switch on the front of the unit. Input 2 has three dual RCA inputs and a front-mounted 3.5mm jack.
- Adjust the volume for each input using the corresponding volume pot on the front of the unit.
- If using Input 1 for mic or line input operation, adjust the input sensitivity using DIP switch 7 for the dual RCA line input and adjust the volume using the Input 1 volume pot on the front of the unit.
- If using Vox sensitivity, set it to ON via DIP switch 8. Input 2 will be muted when audio at Input 1 is present. Adjust the sensitivity of the Vox circuit via the trimpot.
- If using auxiliary RCA inputs on Input 2, adjust the input sensitivity using DIP switches 4-6.
- If powered from 24V DC, use the resettable DC fuse to protect the unit. Press the red button to reset the fuse.
OVERVIEW
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 a 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.
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
- Overvoltage limiting
- On-demand fan cooling (60W and 100W versions only)
- Temperature shut down protection
- Dual input connectors
- Variable input sensitivities
- 240V ac / 24V dc operation
- Australian designed & manufactured
REAR PANEL
-
240V AC Input
Connect to a 220-240V AC @ 50Hz power source. -
100V Output
Speakers fitted with a 100V line transformer may be connected. Always ensure that the toal load of the speakers does not exceed the rated output of the amplifier ie 333Ω minimum at 100V for the A 4235A (30W), 166Ω minimum at 100V for the A 4245A (60W) and 100Ω minimum at 100V for the A 4255A (100W). 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 connections to the wrong terminals. Refer to Fig 2 and Fig 3 for more details about the impedance of speakers and how to check the impedance. -
Input 2
Input 2 consists of 3 sets of Dual RCA inputs and a front-mounted 3.5mm jack. Each of these inputs has an adjustable input sensitivity of either 300mV or 1V set by DIP switches 4-6. The input is selected by the rotary switch on the front of the unit which has four positions. Three of the positions select the three RCA inputs and the fourth position selects the music input on the front of the unit. Volume is adjusted by the Input 2 volume pot on the front of the unit. -
DIP Switch Settings
The A 4235A/45A/55A range of amplifiers have a set of options that are enabled via the DIP switches 1-8.
Switch 1-3 Not used
Switch 4-6 sets the input sensitivity for the Auxiliary RCA inputs on Input 2 to either 1V or 300mV.
Switch 7 sets the input sensitivity for the Dual RCA line input to either 1V or 300mV.
Note: this only affects the line input.
Switch 8 Input 1 can be set to Vox Input 2 and is switched on via DIP 8. -
Vox Sensitivity
When the VOX is set to “ON” via DIP 8, Input 2 is muted when audio at Input 1 is present. The sensitivity of the VOX circuit is adjusted via this trimpot. -
Input 1
Input 1 can be used for mic or line input operation. The dual RCA line input has an adjustable line input sensitivity of either 300mV or 1V (Set by DIP switch 7). The balanced XLR input has an adjustable input sensitivity from 3mV up to 2V. Phantom power is available on the balanced XLR input. Volume is adjusted via the Input 1 volume pot on the front of the unit. -
Resettable DC Fuse
Used to protect the unit when powered from 24V DC. This fuse is resettable by pressing the red button. -
24V DC Input
Battery Backup: Provision has been provided to run the amplifier 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.
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 30 watts
for the A 4235A, 60 watts for the A 4245A and 100 watts for the A 4255A
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 2 lists the impedance at
certain loads of speakers fitted with 70V and 100V line transformers. So for a
total load of 60 watts using 100V line transformer fitted speakers, the
impedance of the speaker load should be 166Ω.
TROUBLESHOOTING
If the REDBACK amplifier fails to deliver the rated performance, check the following:
No Power, No Lights
Make sure the amplifier power switch is on. Make sure the mains power switch
is on at the wall. Check the mains and DC fuse. Replace with only the correct
type and rating. Overrated fuses with invalidated 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 and check the
speaker line impedance. Note you must use an impedance meter for this such as
Redback Q 2004 Impedance Meter.
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 input DIP switches are set correctly.
Continually Blows Fuses
Make sure that the speaker line is not shorted. Check speaker types, ratings
and if on correct output.
The amplifier Keeps Cutting In & Out
Make sure that there is adequate ventilation around the amplifier. Check the
vent slots on the top and sides are not covered or blocked and the fan is
functioning correctly. Check also speaker types, ratings and for any short
circuits on the speaker line.
SPECIFICATIONS
POWER OUTPUTS
A 4235A: ………………………………………………30 watts RMS
A 4245A: ………………………………………………60 watts RMS
A 4255A: …………………………………………….100 watts RMS
Distortion:…………………………………………..< 0.5%, @ 1kHz
FREQUENCY RESPONSE
Mic input:……………………………………….50Hz – 12kHz, -3dB
Line input: ……………………………………..50Hz – 15kHz, -3dB
SENSITIVITY
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
Input1: …………………………..3 pin XLR balanced or 2 x RCA
Input2: …………………………………..3 x RCA and 3.5mm Jack
24V DC power: ……………………………………Screw terminals
240V AC power: …………………………. IEC power connector
WEIGHT
A 4235A: ………………………………………………………. ≈4.5kg
A 4245A: ………………………………………………………. ≈5.5kg
A 4255A: ………………………………………………………. ≈6.0kg
DIMENSIONS: ……………………………≈ 483W x 210D x 44H
References
Read User Manual Online (PDF format)
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