REDBACK
A 4075-85
Page 2
BL2074
O
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.
O
PTIONS AND
F
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
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 600
Ω
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 RCA
ʼ
s 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 500
Ω
-1k
Ω
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.
