Studio Technologies 45A - Manual (Page 15)

Model 45A User Guide Issue 2, November 2011
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
connected 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
operation. (Approximately 500 milliam-
peres of this current is used for the 2-wire
party-line intercom power source feature.)
Included with each Model 45A is a univer-
sal mains input/24 volt DC output power
supply. The power supply’s DC output
cable has been terminated with a Switch-
craft® 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 important, 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-type
inlet connector. 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-type connector on
the other. Units intended 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 Con-
figuration 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 belt packs the Model 45A
is a power “hog,” requiring the aforemen-
tioned 175 milliamperes of DC current for
operation. The other requirement is that