www.redbackaudio.com.au
Redback® Proudly Made In Australia
7
Redback® A 4270/80
Four Zone Paging PA Amplifier
9.0 REMOTE VOLUME (Optional)
It is possible to control the master volume with the addition of the A 4373 Digital Remote volume board and a 1k
Ω
potentiometer (or Altronics A 2280B wall plate) fitted across the terminals labelled “Optional Plugin” on the rear of the
amplifier. The plugin board is fitted inside the amplifier in the location shown in figure 4.
NOTE: Take special care with the orientation of the board and remove power from the amplifier before fitting.
Fig 4
Fig 5
PHANTOM POWER
DIP SWITCHES
1=MIC1
2=MIC2
3=MIC3
VOX1
VOX2
ON
OFF
ON
OFF
EARTH
LIFT
SWITCH
EARTH
LIFT
PL
UGIN
PL
UGIN
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 2003 or similar impedance meter.
About 70V & 100V Line Speaker Systems
Load 70V 100V
0.5W 9.4kΩ 20k Ω
0.66W 7.12kΩ 15k Ω
1W 4.7kΩ 10k Ω
1.25W 3.76kΩ 8k Ω
2W 2.35kΩ 5k Ω
2.5W 1.88kΩ 4k Ω
3W 1.56kΩ 3.3k Ω
5W 940Ω 2k Ω
7.5W 626Ω 1.3k Ω
10W 470Ω 1k Ω
15W 313Ω 666 Ω
20W 235Ω 500 Ω
30W 156Ω 333 Ω
40W 117Ω 250 Ω
60W 78Ω 166 Ω
100W 47Ω 100 Ω
125W 37Ω 80 Ω
250W 19Ω 40 Ω
500W 9.4Ω 20 Ω
