Studio Technologies 770 - Manual (Page 9)

Model 770 User Guide Issue 1, October 1997
Studio Technologies, Inc. Page 9
Model 770
audio level is displayed by a 5-segment
LED meter, while interrupt activity is dis-
played by an LED indicator.
Unique to the Model 770 is the ability to
use each of the IFB section’s seven pos-
sible audio sources as a program or an
interrupt source. A voice-operated (VOX)
circuit monitors the interrupt bus for signal
activity. Whenever a signal meets the
requisite parameters, it is connected to
the IFB output. Using a carefully designed
fast-attack/slow-release circuit results in
very good interrupt audio performance.
Whenever interrupt is active, the program
source can be configured to either fully
mute, or be reduced in level (“dimmed”)
by 10dB. While a full mute is normally
desired, the “dim” mode can serve special
applications, such as sports events.
The IFB section doesn’t take a “back seat”
when it comes to audio quality. Sophisti-
cated “ramping” analog switches are used
to ensure “click-free” audio. Studio-quality
limiter/compressor circuits serve the inter-
rupt audio signal and the gooseneck
microphone. These circuits help to mini-
mize level variations, making talent cues
more intelligible and reducing the risk of
abnormally high signal levels from reach-
ing the talent’s ears.
Audio Sources
Seven audio signals can be selected to
serve as IFB program or interrupt sources:
the mixer section’s main and AUX bus,
four external line-level inputs, and an
internal telephone interface. More than
one input can be simultaneously selected
to create a mix of signals for program or
interrupt audio. Without external patching
or connections, the Model 770’s main and
AUX audio buses can be directly assigned
as program or interrupt sources. Four
external line-level inputs allow a variety of
audio sources to be connected. For assis-
tance during installation, input level trim
pots, located on the back panel, allow the
nominal “+4” input level to be adjusted
over a ±8dB range.
Telephone Interface
The Model 770 contains a telephone
interface that, using an 8-bit micro-control-
ler integrated circuit, is powerful yet simple
to use. Overall, the telephone interface is
designed to receive audio signals for use
by the IFB section, or to send out audio
from the IFB or mixer sections. A front-
panel switch selects if receive audio will
serve as a program or interrupt source,
or if the telco interface will send audio.
The receive level of the telephone interface
is adjustable using a trim pot located on
the front panel. DIP switches, located on
the back panel, allow the selection of main
bus, AUX bus, or IFB audio as the send
source. For operator assistance, a push-
button switch allows voice signals from
the gooseneck microphone to be sent out
the telephone interface. This “talk-to-telco”
function is extremely useful, especially
when an IFB connection is initially being
established with a remote facility.
The telephone interface is unique in that it
allows two very different telephone “lines”
to be correctly interfaced, meeting the
needs of contemporary installations. The
two operating modes make the interface
compatible with telephone lines or stan-
dard audio signals. When set to the telco
mode, the interface is compatible with
2-wire loop-start DC-biased (“wet”) tip-
and-ring circuits. When set to the standard
audio mode, the interface is directly com-
patible with audio signals provided by
many cellular or satellite telephones.