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Issue Preliminary 2, March 2009 Model 45 User Guide
Page 10 Studio Technologies, Inc.
The next step was to identify resources
that would improve the installation process
and make operation more reliable. This
led to the use of standard 3-pin XLR-type
audio connectors, enabling rapid installa-
tion and troubleshooting in any locale. The
inclusion of LED level meters allowed con-
tinuous monitoring of the input and output
signals. Additional status LEDs were also
deemed to be valuable. Configuration DIP
switches would allow crucial operating
modes to be selected.
A subtle but critical requirement was the
need for the Model 45 to receive its oper-
ating power from either an external 24 volt
DC source or the connected 2-wire party-
line intercom circuit. It also turned out that
in many applications only a small number
of user devices, such as belt packs, were
typically connected to a 2-wire party-line
circuit. So by adding a DC power source
to the Model 45’s 2-wire interface the need
for an external intercom power supply
could often be eliminated.
The final step was to create a physical
package that would provide significant
resources in a format that allowed simple
and reliable integration with other equip-
ment. This was accomplished by speci-
fying a convenient half-rack form factor
which would be excellent for “thrown-
down” use. And by creating two “1U”
rack-mount options, it would be possible
to install one or two Model 45 units in one
space of a 19-inch rack.
Installation
In this section you will be preparing the
Model 45 for use. Since the standard unit
is housed in a self-contained enclosure,
getting it ready for use in portable appli-
cations requires only making a few inter-
connections. These include 4-wire audio
input, 4-wire audio output, and 2-wire
party-line intercom connections that use
3-pin XLR-type connectors. In many ap-
plications an external source of 24 volts
DC will be connected using the supplied
power adapter.
For permanent installations one or two
Model 45 units can be mounted in one
of the optional rack panel adapters. The
resulting one-rack-space unit will be
mounted in an equipment rack.
Shipping Carton Contents
The shipping carton contains a Model
45 Interface, a universal input/24 volt DC
output power supply, one set of self-stick
protective bumpers, and a user guide. A
North-American standard mains power
cord will be provided for use with the
power supply. If necessary, the dealer or
distributor will provide an AC mains cord
that is appropriate for your location. If a
rack-mount front panel is going to be used
as part of the installation it will typically be
shipped in a separate carton.
Locating the Model 45
The location of the Model 45 will dictate
the length of the cable runs needed to link
the unit with the other required intercom
devices. This factor really only relates to
the 2-wire party-line intercom circuit.
These circuits carry unbalanced audio
which can be susceptible to interference
and crosstalk issues. And since party-line
intercom circuits typically carry DC power
a voltage drop due to resistive loss can
become an issue. In general, minimizing
the length of the 2-wire party-line intercom