Studio Technologies 47A - Manual (Page 11)

Model 47A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 11
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-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 compatible with signals that
have a nominal level of 0, +4, +6, or +8
dBu. Configuration DIP switches, located
on the Model 47A’s front panel, allow the
circuitry to be adjusted to match the con-
nected nominal level. The DIP switches
work in tandem to control both the line
input and line output nominal levels.
Audio sources are connected to the line
inputs by way of 3-pin female XLR con-
nectors which are located on the unit’s
back panel. Refer to Figure 1 for a detailed
view. Note that pin 1 of these connectors
is internally connected to the Model 47A’s
earth/chassis ground point.
Prepare the mating connectors (males)
so that 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 potential ground current
path from the Model 47A’s earth/chassis
ground point through the shield of a cable.
Also, if a hum or noise issue does arise be
certain to confirm that, unless absolutely
necessary, the mating connector’s “shell”
isn’t connected to the cable’s shield or pin
1. The 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
pin 2 to signal high (+ or hot) and both
pins 1 and 3 to shield. If connecting an
unbalanced source in this manner results
in hum or noise, connect pin 2 to high
(+ or hot) and pin 3 to shield; leave pin 1
unterminated.
4-Wire Line Outputs
Each of the Model 47A’s two interfaces pro-
vides two analog line-level audio outputs.
These outputs are intended to be connect-
ed to inputs on the devices associated with
the 4-wire audio signals. The outputs are
capacitor coupled, transformer balanced
with a nominal level of 0, +4, +6, or +8
dBu. As previously mentioned, the 4-wire
nominal level configuration DIP switches,
located on the Model 47A’s front panel,
control the level of both the line outputs
Figure 1. Detail of back panel showing line inputs and outputs