Manual

Model 45A User Guide Issue 3, August 2015
Studio Technologies, Inc. Page 15
Model 45A Power Source
The Model 45A requires power for opera-
tion 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 45A 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 con-
nected it always takes priority
. And,
depending on how the Model 45A is
configured, the Model 45A can automati-
cally 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 45A might have a
momentary power outage (approximately
one second) before again going through
the start-up process. Only after this pro-
cess has completed will operation again
commence.
External 24 Volts as the Power Source
As previously discussed, the Model 45A
can be powered by a source of 24 volts
DC. A “locking” 2.1 x 5.5 mm coaxial
power jack is located on the back panel
of the unit. The center pin of the jack is the
positive (+) connection. While the require-
ment for the external source is nominally
24 volts, correct operation will take place
over a 20 to 28 volt range. The Model 45A
requires 750 milliamperes for correct op-
eration. (Approximately 500 milliamperes
of this current is used for the 2-wire party-
line intercom power source feature.)
Included with each Model 45A is a universal
mains input/24 volt DC output power supply
.
The power supply’s DC output cable has
been terminated with a Switchcraft® S760K
coaxial power plug. This “locking” type of
plug correctly mates with the Model’s 45A’s
24V DC IN jack. The locking feature is im-
portant, allowing the external power source
to be securely attached to the Model 45A.
A detachable mains cord is used with the
power supply’s 3-pin IEC 320 C14 inlet con-
nector. Included with each Model 45A is a
mains cord with a North-American (NEMA
15L) standard plug on one end and an IEC
320 C13 connector on the other. Units in-
tended for use in other destinations require
that the appropriate cord set be obtained
from the dealer or distributor.
Using the Connected 2-Wire Party-Line
Circuit as the Model 45A’s Power Source
The connected 2-wire party-line intercom
circuit can be used to provide the Model
45A’s operating power. The acceptable
voltage range is 24 to 32 volts DC, with a
required current draw of 175 milliamperes.
Note that for the Model 45A to be powered
by the connected 2-wire intercom circuit
configuration DIP switch 1 must be in its on
(up) position. Please refer to the Configura-
tion section of this user guide for additional
details.
Before blithely going ahead and powering
the Model 45A with a party-line circuit, it’s
important to review the possible pitfalls of
this arrangement. First of all, compared to
most intercom beltpacks the Model 45A
is a power “hog,” requiring the aforemen-
tioned 175 milliamperes of DC current for
operation. The other requirement is that
the supplied voltage must be 24 volts or
greater as measured directly at the Model