www.redbackaudio.com.au
Redback® Proudly Made In Australia
6
Redback® A 4377/87
Four Input Public Address Amplifier
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 125 watts for the A 4377
and 250 watts for the A 4387 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 3 lists the
impedance at certain loads of speakers fitted with 70V and 100V line transformers. So for a total load of 125 watts using
100V line transformer fitted speakers, the impedance of the speaker load should be 80Ω.
Fig 3
AUDIO CONNECTIONS
The amplifier has three balanced XLR audio inputs, three dual RCA line inputs which are internally mixed
to create mono signals and a front mounted Music Input for portable devices. This input when connect-
ed, over-rides the rear channel 3 audio sources and is adjusted via the volume 3 level control.
A VOX function is also included which when enabled will allow input 1 to mute inputs 2 and 3, or input
2 to mute input 3. The VOX circuitry is selected by internal switches as shown in figure 5. The VOX1
switch when set to ON will allow input 1 to mute inputs 2 & 3. The VOX2 switch when set to ON will
allow input 2 to mute input 3. The VOX sensitivity is adjusted by the trimpots located on the front of the
amplifier.
Fig 4 shows a typical install where the A 4377 has a balanced microphone connected to input 1 and a
Line level source connected to input 2. If the VOX1 switch is set to “ON”, the microphone will VOX mute
the CD player connected to input 2.
Fig 4
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. Use the Altronics
Q 2001 or similar impedance meter.
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
240V AC @ 50Hz
RISK OF ELECTRIC SHOCK
OPEN BY QUALIFIED
PERSONNEL ONLY
!
CAUTION
Tape Out
Line 1
Mic 3
Mic 2
Mic 1
1
2
3
1 • Shield
2 • Hot
3 • Cold
MIc XLR
wiring
Configuration
Line 2
Line 3
L
R
L
R
L
R
Output
125W
Fuse
5 Amp
7.5 Amp
250W
AC Fuse (M 205)
DC Fuse
Output
125W
10 Amp
20 Amp
250W
Resettable
DC Fuse
Voice Chime Alert
Over
& Evac
EV
CO
M
CAN
CH
AL
100V
OUT
L
R
Optional
Plugin
- +
+ _
24V
DC IN
Made in Australia by
Altronic Distributors Pty Ltd
www.redbackaudio.com.au
- +
+ _
Speakers fitted with
100V line transformers.
CD
REDBACK
2
1
3
2
1
3
2
1
3
1
2
3
1 • Earth/Shield
2 • Signal Hot
3 • Signal Cold
MIc XLR
wiring
Configuration
