Studio Technologies 41 User Manual

User Guide

Issue 1, October 2004

This User Guide is applicable for serial numbers:

M41-00151 and later

Copyright © 2004 by Studio Technologies, Inc., all rights reserved

www.studio-tech.com

50012-1004, Issue 1

Table of Contents

Introduction ................................................................... 5

Installation ..................................................................... 8

Post-Installation ............................................................. 12

Operation ...................................................................... 13

Troubleshooting ............................................................ 15

Technical Notes ............................................................. 17

Specifications ................................................................ 20

Appendix A .................................................................... 21

Block Diagram

Model 41 User Guide Issue 1, October 2004
Studio Technologies, Inc. Page 3

This page intentionally left blank.

Issue 1, October 2004 Model 41 User Guide
Page 4 Studio Technologies, Inc.

Introduction

The Model 41 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 41 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 41’s audio quality is excellent;
little hiss, hum, or other artifacts are pres­ent. To ensure optimal operation, the unit
provides extensive resources for visually
and audibly monitoring the audio and DC
output signals.

Installation of the Model 41 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 interrupt­ible foldback. On its own, the term fold­back is an alternate way of describing a
cue or monitor function. Adding “interrupt­ible” 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 +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. The Model 41 imple­ments wet IFB circuits. As such, in this
user guide the term IFB will always repre­sent this type of circuit.

Model 41 Front Panel

Model 41 Back Panel

Model 41 User Guide Issue 1, October 2004
Studio Technologies, Inc. Page 5

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 41 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 41 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 41’s
audio inputs are compatible with standard
line-level audio signals virtually any analog
source can be connected.

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 “program­with-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 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 41 design goal—the
hiss, hum, and noise associated with
typical IFB circuits 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 signal.

Four Independent IFB Circuits

The Model 41 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 +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 feed user cue signals

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 41
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 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

Issue 1, October 2004 Model 41 User Guide
Page 6 Studio Technologies, Inc.

The Model 41’s IFB circuits provide DC

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.

Monitor Section

To help ensure proper installation and
operation, the Model 41 includes a sophis­ticated monitor section. Two 5-segment
LED meters provide an indication of the
IFB audio levels as they appear directly on
the output connectors. This unique feature
makes it simple to adjust and maintain the
correct level of the audio sources so as to
provide optimal IFB performance. A head­phone output is also provided, allowing
“real world” checking of IFB audio quality.
In addition to being able to manually
select the IFB circuit to be monitored by
the meters and headphones, an “auto
scan” mode is included. This allows each
of the four IFB circuits to be monitored in
a continuously repeating sequence.

The DC output voltage present on pin 2
of each IFB circuit is also monitored. Four
LED indicators, one for each IFB circuit,
will “flash” if the voltage on its associ­ated IFB circuit falls below the acceptable
value. Over-current or short-circuit condi­tions will no longer fall “below the radar,”
causing problems for IFB device users
with little chance of early detection.

Compatibility

The Model 41 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 41’s audio inputs.
With the Model 41’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 41 the intercom system’s audio
quality can be maintained all the way to
the IFB users.

The Model 41’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 41 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 41’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

Model 41 User Guide Issue 1, October 2004
Studio Technologies, Inc. Page 7

be supported. Each of the four Model 41
IFB circuits will support up to six Model 35
Talent Amplifiers.

Installation

In this section you will be installing
and interconnecting the Model 41. The
one-rack-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 41’s 3-pin IEC
320 C14-type inlet connector.

System Components

minimize cable length. In general, shorter
cables will lead to more reliable and
consistent system performance. It’s also
helpful if a technician can readily view and
access the monitor section that is located
on the right side of the Model 41’s front
panel. The output status LEDs and levels
meters can serve important roles in ensur­ing correct IFB circuit operation. Access
to the headphone output jack and level
control can also be useful.

Mounting the Model 41

Once the desired mounting location has
been selected, the Model 41 will require
one space (1.75 vertical inches) in a stan­dard 19-inch (48.3 cm) equipment rack.
Secure the unit into the equipment rack
using two mounting screws per side.

The shipping carton contains the Model
41 Interface and associated user guide.
Units destined for North America and
Japan also include an AC mains cord.
Your dealer or distributor should provide
an AC mains cord for other destinations.

Locating the Model 41

The Model 41’s IFB circuits provide DC
power and unbalanced audio to operate
external IFB user devices. These devices
are often IFB “belt packs,” broadcast
announcer consoles, or other “talkback
boxes.” The Model 41’s mounting loca­tion will dictate the length of the cable
runs needed to link the unit with the con­nected devices. In some cases the loca­tion choice is already established. For
example, in field broadcast applications
the Model 41 will almost always be located
in a production truck or trailer. But in fixed
applications it may be possible to select
the Model 41’s mounting location so as to

Audio Input Connections

The Model 41 has eight line-level audio
inputs, arranged as four 2-channel pairs.
Each pair serves one of the four IFB cir­cuits. Each IFB circuit, along with its two
associated audio inputs, is completely
independent. Literally any audio source
with a nominal operating level of +4 dBu
can be successfully connected. Trans­former coupled, the inputs are compat­ible with balanced or unbalanced signals.
In many applications the analog outputs
from digital matrix intercom systems will
be connected to the Model 41.

For on-air television applications the IFB
sources are generally configured to pro­vide a single- or dual-channel cue “feed”
to talent personnel. In such cases channel
one of a pair is generally designated as
the “interrupt” channel while channel two
is the “program” channel. For other broad­cast applications, such as live radio, it’s
possible that a stereo cue source will be

Issue 1, October 2004 Model 41 User Guide
Page 8 Studio Technologies, Inc.