Studio Technologies 47 - Manual (Page 11)

Model 47 User Guide Issue 1, August 2010
Studio Technologies, Inc. Page 11
4-Wire Line Inputs
As previously mentioned, each of the
Model 47’s two interfaces 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-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 47’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 47’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 remov-
ing the shield connection from pin 1 can
eliminate the issue; “floating” pin 1 will
remove a potential ground current path
from the Model 47’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 neces-
sary, 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 47’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 47’s front panel, con-
trol the level of both the line outputs and
the line inputs. The 4-wire line outputs are
capable of driving inputs that have imped-
ances as low as 600 ohms, however con-
necting to loads of 2 k ohms or greater is
preferred. The line outputs are connected
by way of 3-pin male XLR connectors which
are located on the Model 47’s back panel.
Refer to Figure 1 for a detailed view.
The mating connectors (females) should
be prepared so that signal high (+ or hot)
is expected on pin 2. Signal low (– or cold)
should be expected on pin 3. A cable’s
shield can be connected to pin 1. How-
ever, in order to minimize the chance that
ground-interaction problems will arise, pin
1 on each of the line output connectors
is isolated from all Model 47 circuitry and
ground points. “Floating” pin 1 virtually
eliminates the chance that a “ground loop”
problem will occur.