Altronics A 4075 User manual

BL2074
A 4075 125W
A 4085 250W
6 Input Mixer Amplifiers
®
www.altronics.com.au
Congratulations on purchasing a REDBACK
Phase 4 Public Address Mixer Amplifier.
Engineered and manufactured to high standards this
unit will provide you with many years of trouble
free use.
A 4075 125 Watt Mixer Amplifier
A 4085 250 Watt Mixer Amplifier
FEATURES:
• Latest design and technology
• Very low noise and distortion
• 70V, 100V and 4-16 Ohm outputs
• 240V AC or 24V DC operation
• Rack mountable
• Thermal overload protection
• Thermally cued forced fan cooling
Inputs and Outputs
Inputs 1-6 can be configured for balanced microphone or line
use as desired. 3 pin XLR and dual RCA sockets are provided
for each of these inputs. Outputs are 600Ω/0dBm 3 pin
balanced XLR or dual RCA sockets for record/tape out.
Input Configuration
Inputs 1-6 include an individual 4 way dip switch enabling
selection of mic or line input operation, adjustable line input
sensitivity (100mV or 1V), Priority/VOX muting for inputs 1-3
(see below for priority details) and phantom power on/off.
Priority/VOX muting is not available on inputs 4-6.
Note, when the Priority/VOX muting function is selected (inputs
1-3) it will operate with the input set for either microphone or
line operation.
Speaker Connections
Speakers with total impedance of 4 to 16 ohms, or speakers fit-
ted with a 70V/100V line transformer may be connected. Always
ensure that the total load of the speakers does not exceed the
rated output of the amplifier ie either 4Ωminimum for the 4-16Ω
terminals or 80Ωminimum at 100V for the A 4075 (125W) and
40 Ωminimum at 100V for the A 4085 (250W). 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.
Power Supply
Ensure power is switched off at the front panel of the amplifier.
Connect either mains power to the IEC socket with the supplied
power lead, or 24V DC to the screw terminals on the rear of the
amplifier. High currents may be drawn (8.5 amps for the A 4075
and 18 amps for the A 4085). Therefore when operating from a
24V DC power supply, confirm the capacity of the DC power
supply used.
Optional Modules
Alert, evacuation and chime tones are available with the
installation of the optional A 2073 tone generator.
Front Panel LED Display
There are six indicators on the front panel, they are ;
1) A ten point LED VU display to indicate output level.
2) A signal LED to indicate any signal present at any of the
inputs (1 to 6).
3) Overtemperature LED indicating if there is a fault such as the
amplifier overheating or a short circuit on the speakers.
4) Peak LED. See below for more details on peak limiting
5) Overload LED indicates when the wattage of connected
speakers exceeds the rated wattage of the amplifier.
6) Power on LED indicates that there is power (24VDC or
mains) to the amplifier.
Operating Instructions

REDBACK A 4075-85
Page 2 BL2074
OPERATION
Remove the mixer from its packaging and inspect for any dam-
age. If the unit appears to be damaged then do not operate as
this may damage the unit further.
1. Prior to installation, set input configurations as desired via
the DIP switches on rear of unit. Table 1 shows the various
settings.
2. Plug in a low impedance microphone into the microphone
input, or a music source (tape or Compact Disc or similar)
into the line input.
3. Turn all controls fully down and then switch the amplifier on.
4. Turn up the level control associated with the input that you
are using to about half way. Talk into the microphone (or
play some music) and adjust the Master level control to
achieve the required volume.
For the best sound performance turn the input level control to a
high setting (say 3/4 ) and use the Master as the volume con-
trol. Use the other input level controls to set the required mixing
ratios. Adjust the bass and treble controls to obtain the desired
sound. For best performance when using long lines between
microphones/mixer and or amplifier use balanced lines. These
reduce noise or hum that may be induced into the cables. Note
that a balanced line uses three wires (two signal wires and one
screened earth wire or shield) where an unbalanced cable uses
only one signal wire and a screened earth. See the connection
details (figure 2) for wiring up plugs etc.
Do not tamper with the unit. Warning Mains Voltage is
Present Inside. Leave servicing to qualified personnel.
OPTIONS AND FEATURES
Vox Muting:
Vox muting is available on inputs 1-3. This is selected by DIP
switches 1-3 (See table 1).
Input 1: When VOX is enabled on input 1 it will override all
other inputs (including alert/evac tone module).
Input 2: When VOX is enabled on input 2 it will override inputs
3 to 6 (alert/evac tone module will mix with this input).
Input 3: When VOX is enabled on input 3 it will override inputs
4 to 6.
Inputs 4-6: No VOX
Alert/Evac Tone Module: VOX is always enabled for the
A 2073. It will override inputs 3 to 6 and mix with input 2.
To adjust VOX sensitivity level for input 1 adjust the trimpot on
the rear panel of the amplifier. To adjust VOX sensitivity level
for inputs 2 & 3 adjust the trimpots inside the amplifier on the
front board (see figure 1).
Switched 24V 1A output and PTT (Push to talk) muting.
When set to “On” via the output DIP switch (see table 1) 24V
DC appears at the “24V DC Switched Out” terminals on the rear
panel, whilst the PTT terminals are shorted together. This is
normally done with the switch of a push to talk microphone. The
switched 24V output could be used to control external devices
like remote volume controls with bypass relays for emergency
paging.
Peak Limiting. This feature is both for the protection and ease
of use of the amplifier
Peak limiting stops the amplifier from exceeding its maximum
output level. Conditions that would cause excessive output are
feedback, volume controls turned to maximum, excessive input
signal level, no speaker connected or very low speaker loading.
All of these conditions are potentially destructive to the amplifi-
er.
Peak limiting is protection for the amplifier under all these condi-
tions.
Under normal usage peak limiting will cut in and prevent tempo-
rary overload conditions such as, yelling into a mic or dropping
it, momentary peaks of music through a radio or CD player.
These conditions would cause distortion or loud and unpleasant
bangs or thumps through the speakers
Peak limiting stops these symptoms from occurring. The Peak
led on the front panel lights whenever peak limiting is active.
Phantom power.10V DC phantom power is available for all
microphone inputs. This is set via rear panel DIP switches.
Check Table 1 for details.
Pre - amp send and return. This allows external effects units,
ie Graphic EQ'S , companders or signal processors to be con-
nected to the amplifier. When not using this feature the send
and return outputs must be linked externally (factory fitted). The
amplifier will not work without this link. Only when an external
effects unit is used can it be removed.
Balanced line output. A 3 pin 600Ω1V balanced XLR output is
provided for passing the audio signal on to other slave ampli-
fiers or to record the output of the amplifier. This output can be
set up to be effected (post master volume) by the master vol-
ume control or unaffected (pre master volume). Factory default
setting disables the preout. Consult table 1 for DIP switch set-
tings regarding this function.
Tape Out Dual RCAʼs provided for recording purposes. This
level is pre master volume.
Remote Volume Overall volume can be adjusted by a remotely
located volume control. This requires a two wire figure 8 type
cable and a 500Ω-1kΩpotentiometer connected as shown in
figure 3. Maximum distance 100m.
IMPORTANT NOTE: Remote volume terminal must be
linked when not using the remote volume feature to ensure
the amplifier performs correctly.
Overload. Limiting has been designed into this amplifier to pro-
tect against incorrect load on the speaker outputs damaging the
unit.
Overtemp. When the amplifier reaches a dangerous tempera-
ture the unit will shutdown, preventing damage. If this occurs,
check for short circuits on the speaker line or objects blocking
the amplifiers air vents.
Battery Backup: Provision has been provided to run the ampli-
fier from a suitably rated 24V battery system in the event of a
mains failure. Using appropriately rated cable, connect the bat-
tery to the “24V DC In” terminals.
Battery Charging: The amplifier is provided with a trickle
charge circuit to maintain the batteries in a charged condition.
The charge rate is ≈300mA. Simply link the terminals marked
“link to charge backup battery” on the rear of the amplifier. A flat
battery will generally take overnight to charge, or even longer
depending on the battery capacity.

REDBACK A 4075-85
Page 3
BL2074
Figure 1 : This is a view of the
Mixer PCB (front board) as you
would view it inside the amplifier.
Note: Only channel 2 & 3 VOX lev-
els are provided inside the amplifier.
Channel 1 VOX level is located on
the rear panel.
Alert/Evac
Level
CH2 Vox
Level
CH3 Vox
Level
Metal Shield
Relay
A 2073 header
24VDC Out
Fuse 1A
Figure 2 : This is a view of the Rear PCB as
you would view it inside the amplifier.
It shows the location of the header for the
A 2073 alert/evac tone module
240V AC
N816
AC Fuse
L
R
Mic 5
Aux 5
DIP 5
L
R
Mic 4
Aux 4
DIP 4
L
R
Mic 3
Aux 3
DIP 3
L
R
Mic 2
Aux 2
DIP 2
L
R
Mic 1
Aux 1
DIP 1
L
R
Mic 6
Aux 6
DIP 6
Send
Return
Preamp Out
Tape Out
DIP 7
L
R
Input 1
Vox Level
Voice
Over Chime Alert /
Evac
AlEv Ch GndCan
24V DC In
+
-
Link to
charge
backup
battery.
4-16Ω70V 100V
Remote
Vol. PTT 24VDC
Switched Out
DC
Fuse
*
†
* Remote Vol. : Link must be fitted when remote volume option is not installed.
† Send/Return RCA: Link must be fitted unless effects unit is used.
A 4075-85 Rear Panel Layout
TABLE 1: DIP SWITCH SETTINGS
Input Switches 1-3
Switch Item On Off
1 Input Type Line Mic
2 Line Level 1V 100mV
3 Priority On Off
4 Phan. Pwr On Off
Input Switches 4-6
Switch Item On Off
1 Input Type Line Mic
2 Line Level 1V 100mV
3- - -
4 Phan. Pwr On Off
Output Switch
Switch Item On Off
1 Switched 24VDC Out Off On
2- - -
3 Preout Pre Master Volume On Off
4 Preout Post Master Volume On Off
IMPORTANT NOTE:
Switches 3 & 4 not to be set to On simultaneously.
All switches are factory set to Off position.
Installer to configure to installation requirements.

REDBACK A 4075-85
Page 4 BL2074
Distributed by Altronic Distributors Pty. Ltd. Perth. Western Australia.
Phone: [phone] Fax: [phone] Internet: www.altronics.com.au
POWER OUTPUTS
A 4075: ...........................125 watts RMS
A 4085: ...........................250 watts RMS
Distortion:......................< 0.5%, @ 1kHz
Output line: ...........70V, 100V or 4 - 16Ω
Line output:...........600Ω 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
Mic inputs: ....> 75dB below rated output
Line inputs:...> 81dB below rated output
OUTPUT CONNECTORS
Speakers: ......................Screw terminals
Line out: ..................................3 pin XLR
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 (inputs 1-3)
CONTROLS
Mic inputs:..................................Volume
Line inputs:.................................Volume
Bass:..............................±10dB @ 100Hz
Treble: ...........................±10dB @ 10kHz
Master:........................................Volume
Power:................................On/off switch
Indicators: ..........Power, fault, VU meter,
signal present, output peak limiting, overtemp
Power Supply:..........240V AC or 24V DC
FUSE PROTECTION
A 4075: ...........................5A AC , 10A DC
A 4085: ........................7.5A AC , 20A DC
Switched 24VDC 1A Internal (both models)
DIMENSIONS
All models:............≈483W x 330D x 88H
WEIGHT
A 4075:.......................................≈14.5kg
A 4085:.......................................≈19.5kg
Colour:............................................Black
*Specifications subject to change without notice
Important Note:
This product warranty covers a period of ten years after the date of manufacture. In the unlikely event that the amplifier develops a
fault condition do not attempt to repair the unit. Return it to an authorised service agent or our own service department for repair,
along with proof of purchase. Our contact details are, Phone: [phone], Fax : [phone]
INSTALLING THE TONE GENERATOR
A 2073:
1. Remove lid from unit
2. Unscrew tone generator plate from rear panel
3. Locate tone generator 10 way header on board
(this is located at the rear of the main board)
4. Connect ribbon cable header to the 10 way header
on the rear board of mixer (see fig 2).
5. The tone generator is held in by way of 2 screws
(supplied) through the rear panel (via the same
holes that the tone generator plate was attached).
6. Refit lid and secure with screws.
NOTE: Tones are operated by closing contacts and
remain operating whilst contacts are closed. The
A 2073 assumes priority 2 when installed
Viewed from the front.
To “remote volume”
terminal on amplifier
rear panel.
500to 1k
potentiometer.
Figure 3 : Remote volume connection. Remove link
from remote volume terminals and connect 500Ω-
1K potentiometer.
Maximum distance from amplifier: 100m
TROUBLE SHOOTING
If the REDBACK Phase 4 amplifier fails to deliver the rated performance,
check the following:
No Power, No Lights
Make sure amplifier power switch is on. Make sure mains power switch is
on at the wall. Check the mains and DC fuse. Replace with only the cor-
rect 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.
4-16Ω, 70V or 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 input DIP switches are set correctly.
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, rat-
ings and if on correct output.
Amplifier Keeps on Cutting In & Out
Make sure that there is adequate ventilation around the amplifier. 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.
No Output Volume
Check the Send/Return link is in place. Ensure the input selector dip switch
is configured correctly for each corresponding input.
Ensure remote volume terminals are linked when no remote volume poten-
tiometer is connected.
When connected, check remote volume control is not turned down.
No Switched 24V DC
Check output switch for correct setting.
Check fuse located on rear PCB is not blown.
SPECIFICATIONS