Filter
Top Products
Model 45 User Guide Issue Preliminary 2, March 2009
Studio Technologies, Inc. Page 15
External 24 Volts as the Power Source
As previously discussed, the Model 45 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 requirement for the
external source is nominally 24 volts, correct
operation will take place over a 20 to 28 volt
range. The Model 45 requires 750 milliam-
peres for correct operation. (Approximately
500 milliamperes of this current is used for
the 2-wire party-line intercom power source
feature.)
Included with each Model 45 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 45’s
24V DC IN jack. The locking feature is im-
portant, allowing the external power source
to be securely attached to the Model 45.
A detachable mains cord is used with the
power supply’s 3-pin IEC 320 C14-type
inlet connector. Included with each Model
45 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 desti-
nations require that the appropriate cord set
be obtained from the dealer or distributor.
Using the Connected 2-Wire Party-Line
Circuit as the Model 45’s Power Source
The connected 2-wire party-line intercom
circuit can be used to provide the Model
45’s operating power. The acceptable volt-
age range is 24 to 32 volts DC, with a re-
quired current draw of 175 milliamperes.
Note that for the Model 45 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 45 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 45
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
45’s 2-wire (PL) connectors. Whether the
connected party-line intercom circuit can
provide this much energy will depend on
the characteristics of a specific installation.
The relevant factors include the capacity
of the intercom power supply, the number
and type of connected user devices, and
the length and type of the interconnecting
cables.
The capacity of the intercom power sup-
ply must meet or exceed the needs of the
connected user devices, including the
Model 45. It’s a good idea to perform a
calculation of the total maximum current
draw prior to attempting to install and use
the unit. As a real-time confirmation often
these power supplies have status indica-
tors that can provide a direct indication of
their ability to supply the connected loads.
In many cases the length and type
(gauge) of the interconnecting cable will
be the limiting factor as to whether the
intercom circuit can provide adequate
power for a Model 45. This is because the
intercom circuit’s DC voltage will drop in
direct relation to the length of the intercon-
necting cable. And with the Model 45’s
relatively large current draw this voltage