Studio Technologies 42 - Manual (Page 5)

Issue 1, July 2004 Model 42 User Guide
Page 6 Studio Technologies, Inc.
wet IFB circuit is the type implemented
by the Model 42. As such, in this user
guide the term IFB will always represent
this type of circuit.
IFB circuits provide an effective means
of delivering power and two channels
of audio to user devices by means of
standard audio cables. These cables,
ubiquitous to the audio industry, interface
using 3-pin male and female XLR-type
connectors. With IFB circuits and standard
audio cables it’s a simple matter to sup-
port user devices such as listen-only belt
packs and announcer’s consoles with no
external power source required. Whether
100 or 1000 feet apart, reliable operation
can be provided.
In many cases, the Model 42 Interface will
be used in on-air television applications.
Whether installed in a fixed location or as
part of a remote facility, excellent perfor-
mance can be obtained. In addition, the
Model 42 is applicable for non-broadcast
applications. For example, audio record-
ing and post-production facilities can also
effectively use the unit. Combined with
stereo or mono listen-only belt packs,
also available from Studio Technologies,
a variety of headphone cue systems can
easily be deployed. As the Model 42’s
audio inputs are compatible with standard
line-level audio signals virtually any
analog source can be connected.
Four Independent IFB Circuits
The Model 42 supplies four independent
IFB circuits. Each circuit consists of two
audio inputs and a “wet” IFB output circuit.
The audio inputs are transformer coupled,
have a nominal level of +4dBu, and are
compatible with balanced or unbalanced
sources. In on-air television broadcast
applications the audio sources will often
be analog outputs from matrix intercom
systems. Two sources are typically desig-
nated to feed user cue signals to stereo
or monaural headsets or headphones.
Generally one source is configured in
the matrix intercom system as “interrupt”
while the other is configured as “pro-
gram.” An alternate term often used for
the “interrupt” channel is “program-with-
interrupt.” This may be more descriptive
as the function is actually a program
source that gets interrupted with talkback
audio. The “program” channel is typically
a continuous source of program audio.
An alternate term is “program-only.” For
other applications, the Model 42’s audio
inputs can be connected to a 2-channel
or stereo audio source. This configuration
may prove useful in radio broadcasting,
audio-with-picture, or recording studio
applications.
Maintaining excellent audio performance
was a major Model 42 design goal—the
hiss, hum, and noise associated with
typical IFB circuits was simply not accept-
able. The Model 42 meets those require-
ments with audio that is “on-air” quality:
low distortion, high signal-to-noise ratio,
and ample headroom. On-air talent and
guests, production personnel, and techni-
cians will all appreciate the clean, quiet
cue signal.
The Model 42’s IFB circuits provide DC
power and two channels of unbalanced
audio over a single 3-conductor output.
The DC output is nominally 30 volts with
a maximum rated current of 200 milliam-
peres. A major strength of the Model 42
is the IFB circuit’s ability to effectively
deliver DC power over a variety of condi-
tions. Unlike other interface devices
that use a common but less-than-ideal