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User Guide
Issue 1, July 2004
This User Guide is applicable for serial numbers:
M43-00151 and later
Copyright © 2004 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50020-0704, Issue 1
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Table of Contents
Introduction ................................................................... 5
Setup ............................................................................. 7
Operation ...................................................................... 10
Troubleshooting ............................................................ 10
Technical Notes ............................................................. 12
Specifications ................................................................ 14
Appendix A .................................................................... 16
Block Diagram
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Issue 1, July 2004 Model 43 User Guide
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Introduction
The Model 43 is designed to create a
broadcast-standard IFB circuit from two
line-level audio sources. The unit will find
use in on-air and production broadcast
applications, as well as specialized applications such as post-production, recording
studio, and equipment test and maintenance. The Model 43 is a unique and versatile product, providing the resources to
easily create a high-performance “wet” IFB
circuit in a compact, easy-to-use package.
The Model 43’s audio inputs are compatible
with standard line-level audio sources, including analog outputs associated with digital matrix intercom systems. The unit’s IFB
circuit provides DC power and two analog
audio signals to support a range of IFB user
devices. The audio quality is excellent—little
hiss, hum, or other artifacts are present. The
Model 43 is housed in a rugged aluminum
enclosure, making it suitable for permanent
or temporary applications. All inputs and
outputs interface using industry-standard
3-pin male and female XLR-type connectors. The connectors are manufactured by
Neutrik® and feature gold-paled contacts
and metal housings. A source of 24 volts
DC is required for operation. Included with
each unit is an external wall-mount 24 volt
DC power source.
View showing left and right audio inputs
There may be persons not familiar with
the term IFB. That’s not unreasonable as
it’s a somewhat obscure acronym for interrupted foldback. (It can also be known
as interruptible foldback.) On its own, the
term “foldback” is an alternate way of describing a cue or monitor function. Adding
“interrupted” before it means that the cue
source can be temporarily replaced with
an audio signal originating from a producer, director, or other production personnel. IFB circuits are often used in the
broadcast industry for talent cueing applications, in both studio and field settings.
Both “dry” and “wet” IFB circuits can be
deployed and their characteristics are
worth reviewing. The term “dry” IFB typically refers to a transformer-balanced linelevel audio circuit with a +4 dBu nominal
level. This is essentially a standard audio
circuit that is commonly used to interconnect audio equipment. The term “wet” IFB
refers to a circuit that combines DC power
and one or two channels of analog audio.
The audio is unbalanced with a typical
nominal level of –10 dBu. A wet IFB circuit
is the type implemented by the Model 43.
As such, in this user guide the term IFB
will always indicate a wet circuit.
IFB circuits provide an effective means
View showing 24 volt DC input and IFB circuit
connections
Model 43 User Guide Issue 1, July 2004
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of delivering power and two channels
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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 support user
devices such as listen-only belt packs and
announcer’s consoles with no external
power source required. Whether the distance from the source to the user device is
100 or 1000 feet, reliable operation can be
provided.
In many cases, the Model 43 Interface will
be used in on-air television applications.
No matter if a unit is installed in a fixed
location or as part of a remote facility,
excellent performance can be obtained.
In addition, the Model 43 is applicable for
non-broadcast applications. For example,
audio recording and post-production
facilities can also effectively use the unit.
Combined with stereo or mono listenonly belt packs, also available from Studio
Technologies, a variety of headphone
cue systems can easily be deployed.
Maintenance facilities and test benches
will appreciate having a Model 43 available to provide assistance during the
testing and repair of IFB user devices. As
the unit’s audio inputs are compatible with
standard line-level audio signals virtually
any analog source can be connected.
from matrix intercom systems. If this is the
case, two sources are typically designated
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 “program.” 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 43’s audio inputs can
be connected to one or two monaural
sources, or alternately, to a 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 43 design goal—the
hiss, hum, and noise associated with
typical IFB circuits was simply not acceptable. The Model 43 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 signal.
IFB Circuit
The Model 43 supplies one circuit that
incorporates two audio inputs and a
“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 onair television broadcast applications the
audio sources will often be analog outputs
43’s IFB circuit provides 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 milliamperes. A major
strength of the Model 43 is the IFB circuit’s
ability to effectively deliver DC power over
a variety of conditions. Unlike other interface devices that use a common but lessthan-ideal circuit topology, a unique IFB
Issue 1, July 2004 Model 43 User Guide
Page 6 Studio Technologies, Inc.
As previously covered briefly, the Model