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Model 46 User Guide Issue 2, September 2007
Studio Technologies, Inc. Page 11
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 trans-
mission system. The 4-wire input circuitry
is balanced, capacitor coupled, transform-
er 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 switches,
located on the Model 46’s front panel, al-
low the circuitry to be adjusted to match
the connected nominal level. The switches
work in tandem to control both the input
and output nominal levels.
Audio sources are connected to the line
inputs by way of 3-pin female XLR-type
connectors 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 46’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 46’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 cables’ shield or pin 1.
Termination of this “fourth” pin of a 3-pin
XLR connector is often the cause of seem-
ingly 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 46’s two interfaces
provides two analog line-level audio out-
puts. These outputs are intended to be
connected to inputs on the devices asso-
ciated with the 4-wire audio signals. The
outputs are capacitor coupled, transform-
er balanced with a nominal level of 0, +4,
+6, or +8 dBu. As previously mentioned,
the 4-wire nominal level configuration
switches, located on the Model 46’s front
panel, control the level of both the line
outputs and the line inputs. The 4-wire line
Figure 1. Detail of back panel showing line inputs and outputs