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M120
Installation
Using a constant voltage system – continued
The same principle applies to constant voltage audio systems. A transformer connected to the output of the amplifier
increases the voltage and reduces the output current, allowing the use of long, smaller-diameter cables to link multiple
speakers with step-down transformers. For economy, the 70V standard was adopted in the United States because
electrical conduit is required on lines with voltages greater than 100V peak-to-peak. Commercial sound systems, such as
those installed in schools, office buildings and restaurants, often use a constant voltage distribution system when
multiple loudspeakers are connected in different areas.
Many loudspeakers with transformers are produced by various manufacturers. Most of these loudspeakers provide tap
points on the transformer to allow power to be distributed to the loudspeakers and their levels to be adjusted
separately. Quest Commercial mixer amplifiers have a built-in transformer to step up the output voltage and step down
the current so that multiple speakers (with transformers) can be connected using long cables. Constant tension systems
allow the use of cables from 1 to 1.6 mm in diameter, depending on their length (long cables must be larger in
diameter).
A simple way to represent a constant voltage is to divide the power in Watts of the amplifier by the number of
loudspeakers used. For example, to connect ten loudspeakers to the output of an M120 amplifier, use a loudspeaker
whose transformer provides a tap point of approximately 10 Watts. 120 Watts divided by 10 speakers gives 12 Watts per
loudspeaker, but we must always keep a cushion of about 15 to 20% of the power of the amp to make sure not to
overload the amp.
Connecting speakers
Connect the speakers to the terminal block output connectors on the rear. Never turn on the amplifier when the
speakers are not connected to the outputs. When using the 4 Ohm output, you must connect speakers with a minimum
impedance of 4 Ohms (4 Ohms or more).
For 70V operation, connect the speaker's positive input to the 70V terminal, and the negative input to the COM (ground)
terminal. Then connect the other speakers one after the other in parallel.
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