42
User Guide
Issue 1, July 2004
This User Guide is applicable for serial numbers:
M42-00151 and later
Copyright © 2004 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50125-0704, Issue 1
Table of Contents
Introduction .................................................................. 5
Installation .................................................................... 7
Operation ..................................................................... 11
Troubleshooting ........................................................... 11
Technical Notes ........................................................... 13
Specifications .............................................................. 16
Appendix A .................................................................. 17
Block Diagram
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Introduction
The Model 42 is designed to create
broadcast-standard IFB circuits from linelevel audio sources. The unit’s primary
application is to interface analog outputs
associated with digital matrix intercom
systems with broadcast IFB user devices.
The Model 42 provides four independent
IFB circuits. Each IFB circuit provides DC
power and two analog audio signals to
support the connected IFB user devices.
The Model 42’s audio quality is excellent;
little hiss, hum, or other artifacts are
present. Installation is very simple. Audio
input connections are made using a
25-pin D-subminiature connector. The
IFB output circuits interface using standard
3-pin XLR-type connectors. The compact,
one-rack-space package is constructed
using heavy-gauge steel components.
The unit’s mains power input can range
from 100 to 230 volts, 50/60 hertz. This
“universal input” ensures correct operation
virtually anywhere in the world.
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, both in 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
line-level audio circuit with a +4dBu
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 –10dBu. A
Model 42 Front Panel
Power present
LED
Model 42 Back Panel
AC mains
connection
Model 42 User Guide Issue 1, July 2004
Studio Technologies, Inc. Page 5
IFB output
circuit connections
Audio input
connections
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 support 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 performance can be obtained. In addition, the
Model 42 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 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 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-withinterrupt.” 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 acceptable. The Model 42 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.
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 milliamperes. A major strength of the Model 42
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 less-than-ideal
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circuit topology, a unique IFB circuit was
developed by Studio Technologies to
achieve the desired performance goals.
The result is a major improvement in
effectively supporting IFB user devices
over a wide range of conditions. Connected devices can draw up to the full
rated 200 milliamperes of current with
little drop in DC voltage. This output voltage stability is the key—whether drawing
50, 100, or 200 milliamperes, the output
will remain close to 30 volts. In practical
terms this means that reliable IFB-based
cue systems can now be deployed in
more stadiums, concert halls, or motor
racing facilities than was previously
possible; longer cable runs, more user
devices, excellent performance.
Compatibility
The Model 42 is compatible with virtually
every digital matrix intercom system,
including those from Clear-Com®, Drake,
RTS™, and Riedel Communications.
Interfacing requires only the connection
of analog output ports from the intercom
system to the Model 42’s audio inputs.
With the Model 42’s excellent audio and
power delivery performance it’s an ideal
alternative to the interface devices offered
by the intercom system vendors. Using the
Model 42 the intercom system’s audio
quality can be maintained all the way to
the IFB users.
The Model 42’s IFB circuits allow virtually
every IFB user device to be supported.
These include the Model 30-series listenonly belt packs and Model 200-series
announcer console products from Studio
Technologies. The 200-series units combine a variety of microphone control,
headphone monitoring, IFB and intercom
system interfacing, and related functions
into compact desktop units. Industrystandard listen-only belt packs from RTS,
including the 4020 and 4030, can also be
directly supported.
Alternate Applications
In addition to broadcast intercom applications, the Model 42 can be used to create
high-performance stereo headphone cue
systems. Stereo line-level signals coming
from audio consoles, routing switchers, or
off-air receivers can be connected to the
Model 42’s audio inputs. The IFB circuits
can be connected to listen-only belt packs,
several models of which are available
from Studio Technologies. For example,
the Model 35 Talent Amplifier will allow
one or two pairs of stereo headphones to
be supported. Each of the four Model 42
IFB circuits will support up to six Model 35
Talent Amplifiers.
Installation
In this section you will be installing and
interconnecting the Model 42. The onerack-space unit will be mounted in an
equipment rack. Audio input connections
will be made by way of a 25-pin D-subminiature connector. IFB circuits will be
interfaced using four 3-pin XLR-type
connectors. AC mains power is connected
by means of a detachable cord set that is
compatible with the Model 42’s 3-pin IEC
320 C14-type inlet connector.
System Components
The shipping carton contains the Model 42
Interface and associated user guide. Units
destined for North America and Japan
also include an AC mains cord. Your
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