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Issue Preliminary 2, March 2009 Model 45 User Guide
Page 14 Studio Technologies, Inc.
pin 3 of the Model 45’s 2-wire party-line
intercom interface, will be utilized. Pin 2,
the Model 45’s audio channel 1, will only
be used for connecting DC power to the
connected devices. While the audio resourc-
es provided by channel 1 will not be used,
the Model 45 can still be used to supply DC
power on pin 2. As previously mentioned,
the maximum current draw on the 30 volt
DC output is 300 milliamperes. Alternatively,
an external intercom power supply can
support the connected devices.
In some single-channel 2-wire party-line
intercom system applications it may be
desirable to take full advantage of the two
channels associated with the Model 45’s in-
terface. The Model 45 can certainly be used
in this fashion, but an adapter will need to
be prepared. The recommended connection
method is to create an adapter that “splits”
Model 45’s 2-wire (PL) intercom connector
into two 3-pin XLR connectors, one for each
audio channel. The adapter should use one
female and two male connectors. Pin 1 of a
female 3-pin XLR intended to mate with the
Model 45 will connect to pin 1 of both 3-pin
male XLR connectors. Pin 2 of the female
XLR will go to pin 3 of the male XLR desig-
nated as channel 1. Pin 3 of the female XLR
will go to pin 3 of the male XLR designated
as channel 2. Refer to Figure 5 for details.
Using this adapter the Model 45 can be
directly interconnected with two Clear-Com
intercom circuits. However, power for the
connected devices must be provided by ex-
ternal power sources. The Model 45’s ability
to supply intercom power will not be utilized.
Note: It’s critical that the correct configura-
tion settings be made when using the Model
45’s interfaces to support two independent
intercom circuits. Specifically, the 2-wire
power source configuration DIP switch 2
must be set to its off (down) position. In
addition switch 4, auto terminate disable,
must be placed in its on (up) position.
Refer to the Configuration section of this
user guide for details.
Model 45 Power Source
The Model 45 requires power for operation
of its internal circuitry. This can be provided
by an external source of 24 volts DC or
by way of the connected 2-wire party-line
circuit. As you might expect, if the Model
45 is to serve as the 2-wire party-line power
source an external source of 24 volts DC
must be connected.
When a 24 volt DC power source is
connected it always takes priority. And,
depending on how the Model 45 is con-
figured, the Model 45 can automatically
switch from using the external 24 volt
source to using power from the 2-wire
party-line circuit. While this action can
occur, it is not designed as a power-fail
back-up function. A “seamless” switch
over from using the external 24 volt DC
input to the 2-wire party-line circuit is not
guaranteed. The Model 45 might have a
momentary power outage (approximately
one second) before again going through
the start-up process. Only after this process
has completed will operation again
commence.
Figure 5. Adapter cable wiring diagram