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REDBACK A 4075-85

PERATION

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.

PTIONS AND

EATURES

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

Page 2

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 600Ω 1V 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-1kΩ potentiometer 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.

BL2074