Issue 2, December 2013
Model 42A User Guide
Page 6
Studio Technologies, Inc.
30 to 32 volts. The audio is unbalanced
with a typical nominal level of –10 dBu. The
Model 42A implements “wet” IFB outputs.
As such, in this user guide the term IFB will
always indicate this type of circuit.
IFB outputs provide an effective means of
delivering power and two channels of audio
to user devices by means of standard au-
dio cables. These cables, ubiquitous to the
audio industry, interface using 3-pin male
and female XLR connectors. Using IFB
outputs and standard audio cables it’s a
simple matter to support user devices such
as listen-only beltpacks and announcer’s
consoles with no external power source
required. Whether the IFB source and user
devices are 100 or 1000 feet apart, reliable
operation can almost always be provided.
In many cases, the Model 42A Interface will
be used in on-air television applications.
Whether installed in a fixed location or as
part of a mobile facility, the unit is capable
of providing excellent performance. In
addition, the Model 42A can be used for
non-broadcast applications. For example,
audio recording and post-production facili-
ties can also effectively use the Model 42A.
Combined with stereo or mono listen-only
beltpacks, also available from Studio Tech-
nologies, a variety of headphone cue sys-
tems can easily be deployed. And since the
Model 42A’s audio inputs are compatible
with standard line-level audio signals virtu-
ally any analog source can be connected.
Four Independent IFB Outputs
The Model 42A supplies four independent
IFB outputs. Each circuit consists of two
audio inputs and a 2-channel “wet” IFB
output. The audio inputs are transformer
coupled, have a nominal level of +4 dBu,
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 typi-
cally designated to serve as a 2-channel
user cue signal. Generally one source is
configured in the matrix intercom system
as “interrupt” while the other is configured
as “program.” An alternate term often used
for the “interrupt” channel is “program-
with-interrupt.” This may be more descrip-
tive 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 42A’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 re-
cording studio applications. The specific
application will dictate whether both cue
signals will be utilized by the end user.
In on-air sports broadcast situations a
“double-muff” (stereo) headset will provide
a user with both audio channels, one for
each ear. In interview or news-gathering
applications it’s common to use a single
“earpiece” to provide a user with only
program-with-interrupt audio.
Maintaining excellent audio performance
was a major Model 42A design goal—the
hiss, hum, and noise associated with typi-
cal IFB outputs was simply not acceptable.
The Model 42A meets those requirements
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 technicians will
all appreciate the clean, quiet cue signals.
