Datasheet

Studio Technologies, Inc. Model 41 Interface, Issue 3, Page 2
In many cases, the Model 41 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 41 can be used
for non-broadcast applications. For example, audio recording
and post-production facilities can also effectively use the Model
41. Combined with stereo or mono listen-only beltpacks, also
available from Studio Technologies, a variety of headphone
cue systems can easily be deployed. And since the Model
41’s audio inputs are compatible with standard line-level audio
signals virtually any analog source can be connected.
Four Independent IFB Outputs
The Model 41 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 typically 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 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 41’s audio inputs can be con
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nected to a 2-channel or stereo audio source. This configuration
may prove useful in radio broadcasting, audio-with-picture,
or recording 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
41 design goal—the hiss, hum, and noise associated with
typical IFB outputs was simply not acceptable. The Model 41
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.
The Model 41’s IFB outputs provide power and two channels
of unbalanced audio over a single 3-conductor output. The
output power is 30 volts DC with a maximum current of 220
milliamperes. A major strength of the Model 41 is the IFB
output’s ability to effectively deliver DC power over a variety
of conditions. Unlike other interface devices that use a com-
mon but less-than-ideal circuit topology, a unique IFB output
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 maximum
220 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.
Audio Monitoring
To help confirm proper installation and ensure correct
operation, the Model 41 includes a full-featured audio moni
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tor section. Two 5-segment LED meters provide an indication
of the audio levels as they appear directly on the IFB output
connectors. This capability makes it simple to adjust and
maintain correct audio levels so that optimal IFB performance
can be achieved. A headphone output is also provided, allow
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ing “real world” checking of IFB audio quality. In addition to
being able to manually select the IFB output to be monitored
by the meters and headphone output, an “auto scan” mode is
also included. This allows each of the four IFB outputs to be
monitored in a continuously repeating sequence.
DC Monitoring and Fault Shut Down
To prevent possible damage to the Model 41’s output circuitry
and connected user devices, the DC output voltage present on
pin 2 of each IFB output is continually monitored. If the voltage
on an IFB output falls below 24 volts its associated LED will
“flash” as an error indication. If this under-voltage condition
continues for more than four seconds a shut down mode will be
entered, turning off power to the IFB output. After a 10-second
interval the output will again become active.
Compatibility
The Model 41 is compatible with virtually every digital matrix
intercom system, including those from Clear-Com®, RTS®,
and Riedel®. Interfacing requires only the connection of analog