Individual Circuit Controls; Power Distribution - Pro Intercom MS300 Instructions

Individual Circuit Controls

Each circuit has a control section on the front panel like the one illustrated above. Unless the
Link Switch (see previous section) is in use, each circuit operates completely independently
of the others.
The rotary control marked Local Level controls the volume of the audio on that circuit as
heard in the MS300 user's headset. It does not affect the level that anyone else on that
circuit hears. Each remote station controls its own level.
The Signal button lights the signal lamps on all stations connected to that circuit. Those
stations can also signal the MS300 operator. In both cases the bright yellow LED next to
the button is lit. The Talk button functions momentarily by simply pressing and releasing it.
Tapping it quickly will lock it ON while another tap turns it OFF.

Power Distribution

The MS300 contains a powerful and sophisticated power supply. The upper limit of its
ability to supply current is determined by the toroidal transformer that is at its heart, and its
associated rectifier. The transformer is able to supply (after rectification to DC) 2.4 Amps
@24VDC. This is roughly enough current to drive 80 belt packs with their signal lamps
constantly lit.
Each of the three circuits has its own regulator and is regulated at 1.0A. This means that if
all 3 circuits were loaded to draw their full output. The total would exceed the transformer's
capability by 0.6A. In this event the circuitry would simply begin to reduce the voltage
available from 24VDC down towards 18VDC. The system would not fail and 18VDC is sufficient
to provide beltpack performance close to normal. However, common sense suggests that
any one circuit should be limited to 0.8A. (2.4/3) This represents about 27 beltpacks or 8
LS3 loudspeaker stations. In the very unlikely circumstance that a greater load than this is
required, the stations could be spread across 2 circuits and the link switch used to put them
in communications with one another.
The fact that each circuit has its own regulator means that each circuit can be monitored
separately and that a fault in one circuit will not affect the others.
The Power Supply components are mounted on a massive heat sink and a temperature
sensitive cooling fan starts up if the power supply section gets warm.
In conclusion:
A huge intercom system can be built around an MS300 without fear of
failure.
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