Studio Technologies 750 - Manual (Page 12)

Issue 3, May 1997 Model 750 User Guide
Page 12 Studio Technologies, Inc.
Model 750
electronically balanced, have a nominal
level of +4dBu, and are capable of driving
balanced or unbalanced loads of 600
ohms or greater. Main Output 3 is trans-
former balanced, with its output level
selectable, using a front-panel button, for
microphone or line level. It is capable of
driving full level into balanced or unbal-
anced loads of 2k ohms or greater.
Main Output 1 and 2
Main Output 1 and 2 are intended for
connection to devices located within the
vehicle. It is recommended that either
Main Output 1 or 2 be used as the “on-air”
source. Each output utilizes two ¼-inch
3-conductor phone jacks for interconnec-
tion. Prepare the mating connectors
(plugs) so that tip is signal high (+ or hot),
ring is low (– or cold), and sleeve is shield.
Whether these outputs are wired via the
patch bay will depend on the specific
installation.
Note that while the electronically-balanced
output circuitry is capable of driving loads
of 600 ohms or greater, the output level
will drop slightly as the load impedance
approaches 600 ohms. A 0.5dB difference
in output level can be expected as the
load impedance changes from 10k ohms
to 600 ohms.
While balanced operation is preferred,
unbalanced operation is not a problem
for the electronically-balanced output
circuitry. To connect to an unbalanced
load connect the tip to high (+ or hot),
and both the ring and sleeve to shield. For
optimal unbalanced operation, it is impor-
tant to connect both the ring and sleeve
together on the plug that mates with the
Model 750.
microphone or line-level signals. To mini-
mize noise and other problems, it is rec-
ommended that the mic/line signals aren’t
wired by way of points on the patch bay.
Stereo Line Inputs
The Model 750 contains two stereo line-
level input channels. They are intended
for connection to sources located within
the vehicle, specifically the audio output
channels from videotape machines. The
direct-coupled, electronically-balanced
circuitry has extremely low noise, high
common-mode rejection, but no special
protection from overvoltage or static.
(Don’t get us wrong—the stereo line input
circuitry is better than what’s found on
most audio mixers available today—
they’re just not as “tough” as the mic/line
inputs!) The stereo line input circuitry is
intended for connection to balanced, line-
level signals with a nominal operating level
of +4dBu.
Each stereo line input channel uses two
3-pin female XLR-type connectors. Pre-
pare the mating connectors (males) so
that pin 2 is signal high (+ or hot), pin 3 is
low (– or cold), and pin 1 is shield. With an
unbalanced source connect pin 2 to high
(+ or hot), and pins 1 and 3 to shield. If
connecting to an unbalanced source in
this manner results in hum or noise, con-
nect pin 2 to high (+ or hot) and pin 3 to
shield; leave pin 1 unterminated. For
flexibility of use it is recommended that the
stereo line input connections be routed
through points on the patch bay.
Main Outputs
The Model 750 contains three sets of
stereo outputs associated with the main
audio bus. Main Outputs 1 and 2 are