Studio Technologies 770 - Manual (Page 18)

Issue 1, October 1997 Model 770 User Guide
Page 18 Studio Technologies, Inc.
Model 770
“ground loops” will be isolated, protecting
the Model 770 and related equipment that
is located inside the vehicle.
The IFB line output was designed to pro-
vide a fully isolated output with decent
sonic performance. It was NOT designed
to drive full level into 600 ohm loads! While
a 600 ohm load can be connected without
damage, a 3-4dB level drop should be
expected. Used with 2k ohm or greater
loads, the IFB line output will provide its
full specified performance.
IFB Monitor Output
The IFB monitor output is designed for
connection to an audio power amplifier
associated with a monitor loudspeaker. In
mobile applications it may prove common
for an amplified speaker, such as from
Fostex, to be connected. The IFB monitor
output is similar to the monitor output
associated with the Model 770’s monitor
section. The difference lies with the signal
source. While the monitor section’s moni-
tor output allows the audio source to be
selected from among five choices, the
audio source for the IFB monitor output is
always the IFB signal. By having two
monitor outputs, an operator can monitor
his or her desired source, while ensuring
that important talent cues will not be
missed.
The IFB monitor output is electronically
balanced, line-level, and can drive a bal-
anced or unbalanced load of 600 ohms
or greater. A ¼-inch 3-conductor phone
jack is utilized for interconnection. Prepare
the mating connector (plug) so that tip is
signal high (+ or high), ring is low (– or
cold), and sleeve is shield. To connect to
an unbalanced load connect the plug’s tip
to high (+ or hot), and both the ring and
sleeve to shield. Whether this output is
wired via a patch bay will depend on the
specific installation.
Intercom Link Output
The ability to have IFB audio available on
an intercom system can be very useful for
smaller broadcast applications. But often
an intercom power supply or user station
with a line-level program input isn’t avail-
able for “injecting” the signal into the
system. The intercom link output is de-
signed expressly to allow the Model 770’s
IFB audio signal to be directly connected
to the bus of an intercom system. The
output is a current source with an imped-
ance of 10k ohms, is DC isolated, and has
a level optimized for RTS/Telex intercom
systems. (Note that RTS/Telex specifies
a nominal audio operating level of 0dBu,
but their equipment performs more like
–10dBu nominal systems.)
It is important to understand that the
intercom link output is a current source,
rather than a voltage source. Most inter-
com systems, such as those from RTS/
Telex, utilize a 200 ohm intercom bus
impedance and expect devices that con-
nect to the bus to maintain a source
impedance of 10k ohms or higher.
Connecting a standard, low-impedance
output circuit directly to an intercom bus
will not provide an acceptable audio
“feed.” An additional problem is that the
output circuit may be damaged by the
DC that is present on the intercom bus.
The Model 770’s intercom link output has
the correct characteristics to meet the
challenge—maintaining the correct imped-
ance and being isolated from DC voltage.
The intercom link output is accessible via
a ¼-inch 3-conductor jack. Prepare the