Studio Technologies 45A - Manual (Page 10)

Issue 2, November 2011 Model 45A User Guide
Page 10 Studio Technologies, Inc.
the use of standard 3-pin XLR-type audio
connectors, enabling rapid installation and
troubleshooting in any locale. The inclusion
of LED level meters allowed continuous
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 45A 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 45A’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 specifying
a convenient “1/2-rack” form factor which
would be excellent for “thrown-down” use.
And by creating three “1U” rack-mount
options, it would be possible to install one
or two Model 45A units in one space of
a 19-inch rack or one unit in a special
10.5-inch rack space.
Installation
In this section you will be preparing the
Model 45A for use. Since the standard unit
is housed in a self-contained enclosure,
getting it ready for use in portable applica-
tions requires only making a few intercon-
nections. 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 applications an
external source of 24 volts DC will be con-
nected using the supplied power adapter.
For permanent installations one or two
Model 45A units can be mounted in one
of the optional rack panel adapters. The
resulting one-rack-space unit will be
mounted in either a 19-inch or a special
10.5-inch equipment rack.
Shipping Carton Contents
The shipping carton contains a Model
45A Interface, a universal input/24 volt DC
output power supply, 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 45A
The location of the Model 45A 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
cables will help to ensure more reliable
and consistent intercom system perfor-
mance. The differential (“balanced”) 4-wire
circuits are typically not impacted by the