Studio Technologies 45A - Manual (Page 12)

Issue 2, November 2011 Model 45A User Guide
Page 12 Studio Technologies, Inc.
Attach the 3-position socket to the 3-pin
header located on the main printed circuit
board adjacent to the back panel. Ensure
that the three pins of the header align with
the three openings in the socket. Reattach
the top panel, securing it to the chassis
with the four screws and lock washers. If
required for mounting clearance, remove
the “bump on” protectors from the bottom
of the chassis.
Mounting the dual-unit rack-mount panel
follows the same procedure but applies
to two Model 45A units. Store both of the
removed standard front panels for pos-
sible later use. Note that on the front-panel
graphics one unit is designated as A while
the other is designated as B. This is pro-
vided so that each can be easily identified
during installation, troubleshooting, and
operation.
Once the desired one or two Model 45A
units have been installed in a rack-mount
front panel, the assembly can be mounted
into the designated equipment rack. One
space (“1U” or 1.75 vertical inches) in
either a standard 19-inch or a special
10.5-inch equipment rack is required.
Secure the unit into the equipment rack
using two mounting screws per side.
4-Wire Audio Inputs and
Outputs
Two audio line input and two audio line
output signals are associated with the
4-wire interface section of the Model 45A.
Connections are made using standard
3-pin male and female XLR connectors.
Refer to Appendices A, B, and C for de-
tails on interconnecting with RTS, Riedel,
and Clear-Com matrix intercom systems.
4-Wire Line Inputs
As previously mentioned, the Model 45A’s
4-wire interface allows two analog line-
level audio sources to be connected. The
source for these signals will typically be
ports on a matrix intercom system. It’s
also possible that the signals will come
from other devices, such as a fiber optic
or copper-based audio transmission sys-
tem. The 4-wire input circuitry is balanced,
capacitor coupled, transformer isolated,
and has an impedance of 13 k ohms. The
line inputs are optimized for signals that
have a nominal level of +4 dBu.
Audio sources are connected to the
line inputs by way of 3-pin female XLR-
type connectors which are located on the
Model 45A’s back panel. Refer to Figure 4
for a detailed view.
Prepare the mating connectors (males)
so that XLR pin 2 is signal high (+ or hot),
pin 3 is low (– or cold), and pin 1 is shield.
If connecting a source in this manner
results in hum or noise it’s possible that
removing the shield connection from pin
1 can eliminate the issue; “floating” pin 1
will remove a ground current path from the
Model 45A’s chassis ground point through
the shield of a cable. (Pin 1 on each of the
two input connectors is internally con-
nected to the Model 45A’s earth/chassis
ground point.) Also, if a hum or noise is-
sue does arise be certain to confirm that,
unless absolutely necessary, the mating
connector’s “shell” isn’t connected to the
cables’ shield or pin 1. Termination of this
“fourth” pin of a 3-pin XLR connector is
often the cause of seemingly inexplicable
noise issues.
With an unbalanced source connect XLR
pin 2 to signal high (+ or hot) and both
pins 1 and 3 to shield. If connecting an