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Using A Constant Voltage Speaker System - continued
The same principle is applied in constant voltage
audio systems where a transformer is connected to the
amplifier's output to step up the voltage while lowering
the output current, which allows you to use long runs of
smaller gauge wire to connect to a series of speakers with
step down transformers. For further cost savings, the 70
volt standard was adopted in the US since UL requires the
use of conduit on lines over 100 volts peak. In addition
to 70 volt operation, the ZM Series amplifiers can also
operate 100 volt systems which is a standard in Europe.
Commercial sound systems, like those installed in schools,
office buildings and restaurants, commonly make use
of constant voltage distributed sound systems when a
large number of ceiling speakers are used to cover several
different sound zones.
Today, there are a large number of installation speakers
available from various manufacturers that include
onboard transformers for constant voltage systems.
Many of these models, like the Samson dB300i, include
selectable power taps on the transformer allowing you
to distribute the power efficiently through the number
of installed speakers and also adjust some speakers to
different output levels. The ZM Series amplifiers have built
in transformers on each channel that step up the output
voltage and reduce the current allowing you to connect
to a series of speakers with step down transformers over
long cable runs. Constant voltage systems can use 14 to
18 gauge wire, while smaller gauge (larger diameter) cable
should be used for longer runs.
A simple way to think about using constant voltage is to
divide the total watts available by the number of speakers
you want to use. You could also add up the speaker's step
up transformer wattage to equal 100 watts or less. For
example, if you want to use ten ceiling speakers on one
channel of the ZM Series amplifier, use a ceiling speaker
with a 12-watt transformer tap (120 watts divided by 10
speakers equals 12-watts per speaker).
Typical ceiling speaker with onboard transformer and six
power taps. These power taps also control volume level for
sound balancing.
Designing an Installation Plan
Another example is connecting four of the Samson
dB300i with the transformers wired for 25 watts to
each channel of the ZM Series amplifier.
Following the wiring diagram on the rear of the
dB300i, connect the ground to Common, the Hot lead
to 70 volt input, and finally, run a jumper from 8 ohms
to the 25 watt connection as shown in the diagram
below.
Set up each of the dB300i they same way so that the
four connected speakers equal 100 watts.
The dB300i's rear panel is configured for 70 volt 25 watt
operation.
Now connect the four speakers to each of the
ZM125's output as shown in the diagram below.
7
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