Studio Technologies AN-2 User Manual

Model 2 Central Controller

and Related Components

User Guide

This User Guide is applicable for Model 2 serial numbers:

M2-00151 and later

Issue 7, November 2001

© 2001 by Studio Technologies, Inc., all rights reserved

5520 West Touhy Avenue

Skokie, Illinois 60077 U.S.A.

Telephone [phone]

Fax [phone]

www.studio-tech.com

[e-mail]

50131-1101, Issue 7

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Table of Contents

Foreword .............................................................................................. 5

Introduction ....................................................................................... 7

What This User Guide Covers...................................................... 7

Model 2 Central Controller ........................................................... 8

Model 22 Access Station ............................................................. 11

Model 32 & Model 33 Talent Amplifiers ....................................... 11

Installation ......................................................................................... 12

Locating the Unit .......................................................................... 12

Mounting ....................................................................................... 13

Program Inputs............................................................................. 13

Auxiliary Audio Input .................................................................... 13

Talent Amplifier Output ................................................................ 14

Line Outputs ................................................................................. 14

Connecting Telephone Lines ....................................................... 15

Access Stations .......................................................................... 16

Monitor Output ........................................................................... 18

Connecting AC Mains Power ..................................................... 18

Operation .......................................................................................... 19

The Model 2’s Front-Panel Controls and Indicators ................. 19

It’s Time to Use the System! ...................................................... 22

Technical Notes ................................................................................ 23

Circuit Descriptions .......................................................................... 29

Model 2 Central Controller ......................................................... 29

Model 22 Access Station ........................................................... 38

Model 32 Talent Amplifier .......................................................... 40

Model 33 Talent Amplifier .......................................................... 41

Troubleshooting ............................................................................... 42

Model 2 Central Controller ......................................................... 42

Model 22, Model 32, & Model 33 ............................................... 43

Specifications ................................................................................... 45

Figure 1 — Model 2 Rear Bracket Mounting Hole Location Diagram
Figure 2 — Model 25A 19-Inch Rack Adapter Diagram
Figure 3 — Model 28A Panel Adapter Diagram
Figure 4 — Model 22 Access Station Diagram

Block Diagrams

Model 2 Central Controller

Model 22 Access Station

Model 32 Talent Amplifier

Model 33 Talent Amplifier

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Issue 7, November 2001 Model 2 User Guide
Page 4 Studio Technologies, Inc.

Foreword

Many people contributed to the creation of the Model 2 and related items. In general, a
good time was had by all—with lots of takeout Chinese food eaten in the process! Jim
Cunningham designed most of the analog circuitry. Mitch Budniak did the logic and
power supply work. Al Lux designed the printed circuit boards. Carrie Loving provided
engineering support and kept track of numerous design changes. Fred Roeck designed
the mechanicals and lobbied hard for the color green on the front panel. Joe Urbanczyk
implemented the computerized testing procedures on our Audio Precision System One.

Studio Technologies is receptive to your comments and questions. Please contact me with
your questions, comments, and suggestions. I can be reached by voice at [phone],
fax at [phone], or via the Internet @ www.studio-tech.com.

Sincerely,

Gordon K. Kapes
President

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Issue 7, November 2001 Model 2 User Guide
Page 6 Studio Technologies, Inc.

Introduction

The IFB Plus Series Model 2 Central
Controller from Studio Technologies is a
highly integrated, two-channel IFB (inter­rupted foldback or interrupted feedback)
system contained in a single rack space
unit. It is expressly designed to provide
talent cueing for ENG, SNG, and mobile
production facilities. The performance
and features of the Model 2 reflect the
needs of contemporary applications. Only
after extensive polling of field production
and engineering personnel was the Model
2’s feature group established. We think
you’ll find the Model 2 a great addition
to your facility.

What This User Guide Covers

This User Guide applies to Studio Tech­nologies, Inc. IFB Plus Series Model 2
Central Controllers with a serial number
of M2-00151 and later. If you are install­ing a Model 2 with a serial number of
M2-00122 or earlier, please contact Studio
Technologies to obtain the appropriate
documentation.

This guide is designed to assist you
when installing, configuring, and using
the Model 2 Central Controller. It also
contains detailed service information
and block diagrams. A separate packet,
provided with the User Guide, contains
the schematic diagrams.

The following items will be covered in this
User Guide:

Model 2 Central Controller

An integrated two-channel IFB unit in­tended for applications where space is at
a premium, yet high performance is still
required. The unit contains everything

required to implement a full-featured
system in a single rack space. Includes
multiple program inputs, integral tele­phone interfaces, monitor amplifier, inter­nal interrupt microphone, among many
other features. The unit is powered by
120 or 220/240V, 50/60Hz.

Model 22 Access Station

Used by a producer or director to access
the Model 2’s IFB channels. Allows con­nection of a Studio Technologies Model
11A gooseneck microphone or a line-level
audio source. Contains two lighted push
button switches which display IFB inter­rupt status. Up to four Model 22s can be
connected to and powered by a Model 2
Central Controller. The Model 25A 19-inch
Rack Adapter allows a Model 22 Access
Station and Model 11A gooseneck micro­phone to be mounted in a single 19-inch
rack space. The Model 28A Panel Adapter
allows a Model 22 and Model 11A goose­neck microphone to be installed in an
opening made in a table, equipment
console, etc.

Model 32 & Model 33 Talent Amplifiers

The Model 32 and Model 33 Talent
Amplifiers are self-contained “belt pack”
units that drive talent ear pieces or head­sets. Up to four Model 32 and/or Model 33
Talent Amplifiers can be connected
to, and powered by, a single Model 2
Central Controller.

The Model 32 is intended for use by on-air
personnel, and contains a source switch,
along with an output level control. Either
IFB channel 1 or IFB channel 2 can be
sent to the talent, along with the desired
audio “volume.”

The Model 33 is unique in that a “mix” of
IFB channels 1 and 2 can be created. Two

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 7

level controls, along with a source select
switch, allows camera and production
personnel to hear IFB cues from either
or both channels. This allows IFB signals
intended for both technician and talent
to be simultaneously monitored.

Model 2 Central Controller

Contained in a single rack space unit is
everything required to implement a two­channel IFB system. Features include
multiple program inputs, telephone inter­faces, voice-operated (VOX) interrupt,
level meters, monitor amplifier, and inter­nal interrupt microphone. Up to four
Model 22 Access Stations can be con­nected to the Model 2, allowing producer
or director positions to access the IFB
channels. In addition, up to four Model 32
or Model 33 Talent Amplifiers can be
connected to a Model 2. The Model 32
and 33 allow personnel access to the IFB
channels using a single standard micro­phone cable.

The Model 2 packs numerous features
into a single, 19-inch rack space.
Standard connectors are used through­out, including 3-pin XLR-type, ¼-inch
2-conductor, 9-position D-subminiature,
and modular telephone (RJ11-type)
jacks. Power is supplied by standard
120 or 220/240V (factory configured),
50/60Hz via a detachable cord.

IFB Channels

The Model 2 contains two independent
IFB channels. Each channel has individual
controls and indicators, including program
source select switches, program level
control, 5-segment LED level meter, and
LED status indicators. We’ll describe one
channel in this paragraph. Six switches
allow the four program inputs and incom-

ing audio from the two telephone inter­faces to be selected as program audio.
A level control allows adjustment of the
program audio level relative to the fixed
interrupt audio level. A 5-segment LED
level meter displays the composite IFB
channel audio level, i.e., program and
interrupt audio level. The meter facilitates
the rapid setting of the program level
control, as well as providing a general
indication of the channel’s signal level.

Each channel’s composite IFB audio
signal (program and interrupt audio) is
sent to four places: line output, talent
amplifier output, telephone interface 2,
and monitor amplifier. The line outputs
provide electronically balanced, line-level
signals that interface with external equip­ment via two XLR-type connectors. The
talent amplifier output provides channel 1
and 2 audio, along with +18Vdc power
on one 3-pin XLR-type connector. Any
combination of up to four Model 32 or 33s
can be connected to the talent amplifier
output.

Program Inputs

The Model 2 contains four program inputs.
Each can be individually assigned to the
two IFB channels, with the ability to assign
multiple program inputs to an IFB channel.
Program signals enter the unit via four
XLR-type connectors on the back panel.
The program inputs are electronically
balanced with a nominal input impedance
of 24k ohms. They feature low noise, low
distortion, and high common mode signal
rejection. Each program input has a trim
potentiometer associated with it. The trim
pots, accessible from the back panel,
allow the nominal +4dBu input level to
be adjusted over a ±8dB range.

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Program audio is muted whenever an
interrupt takes place. A sophisticated
analog switch is used to give a noise-free
mute with absolutely no clicks or pops! If
desired, a program “dim,” rather than a full
mute can be implemented by adding two
resistors to the Model 2’s circuit board.

Compressor/Limiters

Each IFB channel contains a studio-quality
compressor/limiter. The compressing
function evens out variations in the inter­rupt audio signals. The limiting function
smoothly controls peak signal levels.
Together, they make talent cues more
intelligible and prevent abnormally high
signal levels from reaching a user’s ears.
The resulting audio quality is very, very
good.

Signal Routing

In the standard configuration, only inter­rupt audio is routed through the compres­sor/limiter before it is sent to the talent
amplifier output, line output, telephone
interface 2, etc. Program audio is routed,
via the program audio level control and
mute/dim circuit, directly to the talent
amplifier output, line output, etc. Thus
the dynamic range of the program signal
is not altered. Some installations may
benefit from the program audio being
routed through the compressor/limiters.
This “leveling” action can improve intelligi­bility of the program audio, especially in
areas of high ambient noise such as news
remotes or sporting events. Resistor
positions on the Model 2’s circuit board
allow a technician to change the audio
flow, routing program audio via the com­pressor/limiters. The only downside is that
this rerouting greatly limits the ability to
adjust the relative level of the program
audio versus the interrupt audio. This is

because the compressor/limiter function
reduces the dynamic range of the pro­gram audio. As the program level control
is turned “up,” the compressor acts to
reduce the signal level! Also, some users
may find the compressed program signal
more fatiguing due to the higher average
audio level.

Telephone Interfaces

The Model 2 contains two telephone
interfaces. Both interfaces can be used
to bring audio into the Model 2 from the
outside world. These two audio signals
can be independently assigned as pro­gram sources for IFB channels 1 and 2,
as well as being used as an input source
for the voice operated (VOX) interrupt
function. Each telephone interface has
a receive level trim potentiometer that
is accessible via access holes in the front
panel. The large variations one finds in
telephone line signal levels make “on
the fly” level trimming a useful feature.
In addition to receiving audio, telephone
interface 2 can be used to originate an
IFB feed. A switch selects if audio will
be received from the outside world, or
if audio from IFB channel 1 or 2 will be
sent out the interface.

The two telephone interfaces contain
a unique feature which allows two very
different types of telephone “lines” to be
correctly interfaced. Each interface can
be independently set to operate in either
the telephone-line mode or the standard­audio mode. A telephone line has the
profile of being a 2-wire, DC-biased (nor­mally –48Vdc) circuit provided by a local
telephone company. A standard audio
signal could be provided by, for example,
a fax adapter associated with a cellular
telephone.

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Studio Technologies, Inc. Page 9

When an interface is set to the telephone­line mode and a DC-biased telephone line
is connected, full monitoring and control
is implemented. Each interface contains
a switch that allows the telephone line to
be seized (taken off hook) or hung up.
Loop current is monitored when the inter­face is off hook. If a disconnect signal
(a momentary break in loop current) is
detected the interface will automatically
return to the on-hook state. Each interface
contains an LED indicator that lights
whenever loop current is detected. Inter­face 2 also implements an auto answer
function, automatically taking the tele­phone line to the off-hook state when
ringing voltage is detected.

In many cases a “telephone line” is actu­ally provided by a cellular telephone. This
cellular telephone may provide an unbi­ased (no DC loop current) audio output.
The standard audio mode was designed
expressly to interface with this “cell
phone” arrangement. In this mode, the
interface’s loop current-specific features
are disabled, and the interface appears
electrically as a transformer coupled
balanced audio input.

When in the standard audio mode,
an interface’s front-panel switches are
inactive. Also inactive is channel 2’s auto
answer function. An LED associated with
each interface displays when the standard
audio mode is selected. Even during
operation in this mode, the loop current
LEDs remain active, serving as a useful
diagnostic tool. They will display if your
“standard audio signal” is actually a tele­phone line!

Voice Operated (VOX) Interrupt

The Model 2 contains circuitry to allow an
audio signal to serve as both an interrupt

audio source and a control signal. This
eliminates the need for a separate push­to-talk button or contact closure. The VOX
feature allows an audio signal from a
remote source, such as a two-way radio
or telephone line, to serve as the interrupt
source. The VOX function was optimized
for detection of audio signals in the voice
band. As voice detection is quite tricky to
perform, great care was taken when de­signing this function.

Three audio sources can serve as the
VOX input: receive audio from telephone
interface 1, receive audio from telephone
interface 2, or the auxiliary audio input.
The auxiliary audio input is a separate
line-level audio input that serves the VOX
circuit only. A 3-position switch selects
which source will be used. A second 3­position switch selects which IFB channel
the VOX interrupt is assigned to, or if the
function is not active. The VOX function
can be assigned to only one IFB channel
at a time. Each IFB channel contains an
LED indicator light to display when a
voice-activated interrupt is taking place.

Internal Interrupt Microphone

Contained behind the Model 2’s front
panel is an internal interrupt microphone.
Associated with the microphone are two
switches, allowing the internal microphone
to interrupt IFB channel 1, channel 2, or
both.

Monitor Section

The Model 2 contains a simple but excel­lent monitor section. At the core is a 4 watt
audio amplifier designed to drive an 8
ohm (or greater) loudspeaker. Associated
with the monitor amplifier is a 3-position
source select switch and a level control.
The switch selects monitoring of IFB
channel 1 or 2, as well as having an off

Issue 7, November 2001 Model 2 User Guide
Page 10 Studio Technologies, Inc.

position. A click-free analog switch mutes
the monitor output whenever the internal
microphone or a Model 22 Access Station,
if installed and configured, is interrupting
either IFB channel.

Model 22 Access Station

The Model 22 Access Station provides
the capability to add up to four additional
interrupt locations. Model 22s are in­tended to be installed at positions conve­nient to producers, directors, or other
personnel who need to “cue” talent and
related personnel. The unit consists of a
metal chassis containing two lighted push­button switches, unbalanced microphone
and balanced line inputs, and status and
control circuitry.

The two high-quality, back lit push-button
switches provide access to the two IFB
channels. The lights in the switches dis­play when an interrupt is taking place on
its respective channel. When a channel is
idle, the light is lit dimly. An input select
switch allows connection of a Model 11A
gooseneck microphone or a line-level
signal. The electronically balanced line­level input allows interfacing with other
communications equipment, such as an
intercom system.

The Model 22 can be configured to mute
the Model 2’s monitor amplifier output.
This function will prevent acoustic feed­back from occurring when a Model 22
is located close to the Model 2’s monitor
speaker.

Model 22 Access Stations are linked to
the Model 2 Central Controller via 9-pin
D-type female connectors. Each access
station contains two connectors, allowing
a simple daisy-chain installation. The nine
leads carry all signals; audio, control,

status lamp (tally), and power. The Model
2 provides all power required by the
access stations. The Model 25A 19-inch
Rack Adapter is available to mount a
Model 22 and a Model 11A gooseneck
microphone in one space of a 19-inch
rack. The Model 28A Panel Adapter allows
a Model 22 and a Model 11A gooseneck
microphone to be mounted in a panel
opening.

Model 32 & Model 33
Talent Amplifiers

The Model 32 and Model 33 Talent Ampli­fiers are self-contained “belt pack” units
that drive talent ear pieces or headsets.
A single 3-conductor microphone-type
cable links the Model 2 with the talent
amplifiers. Each Model 32 and Model 33
contains both a male and female XLR-type
connector, allowing simple “loop through”
connection of multiple units. Up to four
talent amplifiers can be connected to,
and powered by, a single Model 2 Central
Controller. On each talent amplifier the
audio output signal is provided on a stan­dard ¼-inch 2-conductor phone jack. An
LED on each unit lights whenever power
is present, providing setup assistance and
user confidence. Identical in size, each is
housed in a lightweight, yet rugged, alumi­num housing. A belt clip allows it to be
attached to belts, clipboards, scabbards,
pizza boxes, production assistants, etc.
An optional mounting adapter is available,
allowing a Model 32 or 33 to be installed
in a permanent location.

The Model 32 is intended for use by on-air
personnel, and contains a source switch,
along with an output level control. Either
IFB channel 1 or IFB channel 2 can be
sent to the talent, along with the desired
audio “volume.”

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Studio Technologies, Inc. Page 11

The Model 33 is unique in that a “mix” of
IFB channels 1 and 2 can be created. Two
level controls, along with a source select
switch, allows camera and production
personnel to hear IFB cues from either
or both channels. This allows IFB signals
intended for both technician and talent
to be simultaneously monitored.

Installation

In this section you will be installing a
Model 2 Central Controller in an equip­ment rack. In conjunction with the Model
2, up to four Model 22 Access Stations
can be installed. In addition, wiring can
be installed for up to four Model 32 and
33 Talent Amplifiers.

Internally, the Model 2 has no configura­tion switches or trim pots to set. However,
there are several reasons why you may
need to access the “guts” of the unit:

• The factory-selected AC mains voltage
will be either 120 or 220/240V, depend­ing on the shipping destination. It may
need to be revised for your installation.

Refer to the Technical Notes section for
details on revising these conditions.

In addition to the above situations, you
may want to take a look inside and famil­iarize yourself with the unit on the rare
occasion that it may need service. (The
people here in the marketing department
taught us never to say a unit may need to
be fixed—service is much nicer!) We are
proud of how the “guts” of the Model 2
look and how it is constructed so we
encourage you to take a look!

On a more serious side, removing the
Model 2’s cover with the AC mains cord
connected exposes you to hazardous
voltages.

Warning: Never remove the cover
without disconnecting mains power.
We make the assumption that anyone
gaining access to the inside of our
products meets the requirements for
“qualified service personnel”—includ­ing knowledge of safety precautions.

Locating the Unit

• From the factory, the Model 2 is set to
mute program audio when an interrupt
takes place. If desired, a program “dim”
function, rather than mute function, can
be implemented.

• The standard audio routing for each of
the two IFB channels is for the interrupt
audio to be processed by the compres­sor/limiter circuits. Program audio, with
its dynamic range unmodified, is sent
directly to the output circuitry. For
special applications, the program audio
flow can be changed so that it too is
routed through the compressor/limiters.

Issue 7, November 2001 Model 2 User Guide
Page 12 Studio Technologies, Inc.

Physical access and mechanical noise
are the primary factors when choosing
a mounting location. You don’t want
a cooling fan blowing directly onto the
internal microphone, nor do you want the
microphone at the level of your navel. It
is also a good idea to keep the Model 2
physically separated from other electronic
devices that produce strong electrical
fields. As a device that contains high gain
audio stages, hum and noise pickup is
possible through the chassis and associ­ated cabling. Locating the unit away from
devices such as power amplifiers, power
transformers, and lighting controls will
help to avoid pickup of unwanted signals.

Precautions were taken to limit the Model
2’s bandwidth, minimizing the chance for
RF pickup problems.

Mounting

The Model 2 is intended for rack mount­ing, requiring one 1.75-inch (4.5cm) rack
space. It weighs a bit over 10 pounds
(4.7kg), and operates on either 120 or
220/240V, 50/60Hz. The unit is secured to
the front mounting rails of an equipment
rack using two mounting screws per side.
In addition to the front mounting “ears,”
we encourage you to secure the Model 2
from the back. Provision has been made
for this to be easily accomplished. On
each side of the Model 2’s chassis are
two threaded fasteners intended to secure
user-fabricated mounting bars or brackets.
Use standard 8-32 screws to secure the
mounting brackets to the Model 2’s chas­sis. To prevent damage to the Model 2’s
“guts,” limit the screw length so that the
threads extend into the chassis a maxi­mum of ¼-inch. Refer to Figure 1, located
at the end of this guide, for a mechanical
drawing detailing the fastener locations.
This drawing will assist you in fabricating
the mounting brackets.

Program Inputs

The Model 2 allows four line-level program
audio sources to be connected. The input
circuitry is designed for a nominal input
level of +4dBu. A trim potentiometer is
associated with each input, giving a ±8dB
adjustment range. The trim pots are not
intended for precise calibration, but strictly
to allow the program input signals to be
adjusted to the same relative level. A little
attention to setting the trim pots will give
better operational performance. It will
allow an operator, using the front-panel

program switches, to rapidly change pro­gram inputs, while not giving large changes
in level to users listening to the IFB chan­nel. It is anticipated that the trim pots will be
adjusted only upon initial installation or
during maintenance, and are not consid­ered an operator function. Refer to the
Technical Notes section of this guide for
details on setting the trim pots.

Program audio connections are made via
four 3-pin female XLR-type connectors
located on the back panel. The program
input circuitry on the Model 2 is direct
coupled, electronically balanced with an
input impedance of 24k ohms. External
load resistors must be added if your facility
terminates all audio lines, e.g., with 600
ohms. Studio Technologies discourages
terminating audio lines—but if you have to,
you have to! Prepare the mating connec­tors so that pin 2 is positive (+ or hot), pin
3 is negative (– or cold), and pin 1 is shield.
With unbalanced signals connect pin 2 to
positive, and pins 1 and 3 to shield.

Auxiliary Audio Input

The Model 2 allows an auxiliary line-level
audio source to be connected for use with
the voice operated (VOX) interrupt function.
Identical to the program inputs, the auxil­iary input circuitry is designed for a nominal
signal level of +4dBu. A trim pot is associ­ated with the auxiliary input, giving a ±8dB
adjustment range. The pot is not intended
for precise calibration, but strictly to allow
the AUX input level to be adjusted for cor­rect VOX operation. It is anticipated that
this pot will be adjusted only upon initial
installation or during maintenance, and is
not considered an operator function. Refer
to the Technical Notes section of this guide
for details on setting the trim pot.

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 13

The auxiliary audio connection is made
via a 3-pin female XLR-type connector on
the back panel. The auxiliary audio input
circuitry is direct coupled, electronically
balanced with an input impedance of 24k
ohms. An external load resistor must be
added if your facility terminates audio
lines. Prepare the mating connector so
that pin 2 is positive (+ or hot), pin 3 is
negative (– or cold), and pin 1 is shield.
With unbalanced signals connect pin 2
to positive, and pins 1 and 3 to shield.

The VOX interrupt function is quite special­ized and may not be used regularly in
your facility. For maximum flexibility, it may
be best to terminate the auxiliary audio
input to a patch point in the audio patch
bay. In this way, a variety of audio sources
can quickly be selected as the VOX inter­rupt input source. The VOX feature may
sit unused for months or years, but when
you need it there’s no substitute! The
Model 2’s VOX interrupt works quite well,
better than you may think. (Actually better
than we thought, too, until we tested it!)
Try it out and you may soon find more
applications than you expected.

Talent Amplifier Output

The talent amplifier output is designed to
supply power and audio signals for up to
four Model 32 or 33 Talent Amplifiers. The
talent amplifier output exits the Model 2
via one 3-pin male XLR-type connector.
Pin 1 is common, pin 2 is +18Vdc modu­lated with channel 1 audio, and pin 3 is
channel 2 audio. For convenience, it is
expected that the talent amplifier output
will be wired to a main distribution panel,
along with microphone, camera, and other
various connections. This will allow easy
talent amplifier connection using standard
flexible microphone cable. The distribution

panel does not need multiple talent ampli­fier output connectors which are “multed”
from the Model 2’s talent amplifier output.
Each Model 32 and Model 33 Talent
Amplifier has both a female and a male
3-pin XLR-type connector. This allows the
talent amplifier interconnecting cables to
be “looped” through the talent amplifiers.
This will simplify and, in most cases,
reduce the amount of cabling required
to connect multiple talent amplifiers.

Line Outputs

Associated with each of the two IFB
channels is an electronically balanced
line-level output with a nominal signal level
of +4dBu. The line outputs are capable
of driving balanced or unbalanced, low
or high impedance loads. The line outputs
exit the Model 2 via two 3-pin male XLR­type connectors. Prepare the mating
connectors so that pin 2 is positive (+ or
hot), pin 3 is negative (– or cold), and pin
1 is shield. To connect to an unbalanced
load connect pin 2 to positive (+ or hot)
and pins 1 and 3 to shield.

Some installations may use the line out­puts to drive wireless IFB transmitters. In
other installations they may be used for
special applications, such as feeding a
satellite uplink. For maximum flexibility it
is recommended that the line outputs be
wired via audio patch points, even if you
have a dedicated application.

The Model 2’s audio quality and flexibility
make it a useful tool for non-IFB applica­tions. Not to “toot our own horn,” but the
Model 2’s sonic quality is as good as,
if not better than most audio consoles,
tape recorders, etc. As an example, the
frequency response from program input
to line output is better than ±0.5dB from

Issue 7, November 2001 Model 2 User Guide
Page 14 Studio Technologies, Inc.

20Hz to 20kHz. This makes using one of
the IFB channels as a four input, one
output audio source selector for an uplink
application completely valid. Let the
Model 2 become a useful part of your
facility’s “bag of tricks!”

Connecting Telephone Lines

Words of Caution: As with any product,

installing the Model 2 requires a safety
first approach.

Never install telephone wiring
during a lightning storm. Never

install telephone jacks in wet
locations unless the jack is specifically
designed for wet locations. Never touch
non-insulated telephone wires or terminals
unless the telephone line has been dis­connected at the network interface. Use
caution when installing or modifying
telephone lines.

The Model 2 contains two telephone
interfaces which can be individually con­figured to allow connection to a telephone
line or to a standard audio signal. A tele­phone line is designated as such if it has
a DC bias current associated with it. This
type of signal is sometimes referred to as
a “wet” signal. A standard audio signal
is one that is isolated from any source of
DC voltage. Some fax adapters associated
with cellular telephones provide this type
of “telephone” line. A standard audio
signal is sometimes referred to as a
“dry” signal. While this sounds confusing,
contemporary applications sometimes
refer to both types of signals as “telco.”
To a large production vehicle that pulls up
to do a two-week golf tournament, a telco
line is one provided by the local telephone
company on an RJ11 jack. To a mobile
ENG vehicle, a telco signal might come

from a cellular telephone which in most
cases is a standard audio signal.

Here is a review of the important features
of the Model 2’s telephone interfaces:

Interface 1

• Telephone line or standard audio mode
select switch on back panel

• Used to receive audio only

• Receive audio used as program and/or
VOX source

• Front panel ±8dB receive level trim pot

• Switch allows manual off-hook and
hang-up (telephone line mode)

• Auto disconnect upon break in loop
current (telephone line mode)

• Operating mode and loop current
status LEDs

Interface 2

• Telephone line or standard audio mode
select switch on back panel

• Used to receive or send audio

• Receive audio used as program and/or
VOX source

• Sends audio from either IFB channel

• Automatic answer of “ringing” tele­phone line (telephone line mode)

• Auto disconnect upon break in loop
current (telephone line mode)

• Front panel ±8dB receive level trim pot

• Switch allows manual off-hook and
hang-up (telephone line mode)

• Operating mode and loop current
status LEDs

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 15

Setting the mode switches and connect­ing signals is quite easy. Set the tele­phone interface mode switches, located
on the back panel, to the desired mode—
either telephone line or standard audio
signal. Use modular telephone cables to
mate the Model 2’s modular jacks (RJ11­type) with two more RJ11-type jacks.
Technically, the Model 2’s telco interfaces
use 6-position modular jacks with pins 3
and 4 utilized.

If the telephone line mode is selected,
the telco interfaces should, in most cases,
terminate on an access panel of some
sort. This will make rapid termination with
telephone company-provided lines. Be­cause of the presence of high voltage
ringing signals, it is best not to route tele­phone lines through an audio patch bay.

If the standard audio mode is selected,
a direct connection to the source device
is acceptable, but connecting it via audio
patch points provides better flexibility. In
the standard audio mode the interfaces
look like standard, transformer coupled
audio inputs. Interface 1 has an input
impedance of 2200 ohms. Interface 2 has
an input impedance of 2200 ohms in the
receive mode, and 700 ohms in the send
mode. In standard audio mode, the inter­faces are compatible with balanced or
unbalanced signals. No shield connection
is associated with the telephone inter­faces. Audio signals should be connected
to the telco interfaces, via a modular jack
and cable, using shielded cable, with the
shield wire connected to the appropriate
point at the end opposite of the Model 2.
The shield wire should remain unterminat­ed at the Model 2’s end.

The telco interfaces are designed to
receive and, in the case of interface 2,

send audio signals at nominal levels
that are correct for telephone circuits,
but which are far lower than the typical
+4dBu professional audio standard. The
nominal receive signal level is expected
to be –15dBu, the transmit level is –6dBu.
Trim pots are associated with both inter­faces, allowing the receive level to be
adjusted over a ±8dB range. Special
precautions may need to be taken when
an interface is set for standard audio
mode and +4dBu signals are going to be
connected. These would include the use
of an audio attenuator or “pad” for con­necting receive audio, and the use of a
line amplifier to achieve send gain from
interface 2.

Access Stations

The Model 2 allows the connection of
up to four Model 22 Access Stations. The
Model 22 provides an unbalanced micro­phone input, a balanced line-level input,
two lighted push button switches, and
related circuitry to access the two IFB
channels. Power is provided by the
Model 2, so an external power source
is not required. Nine-pin D-subminiature
connectors link the Model 22 with the
Model 2 Central Controller and, if desired,
another Model 22. A 5-position screw
terminal strip allows connection of a
Studio Technologies Model 11A goose­neck microphone or a line-level signal.

There are three mounting methods appro­priate for the Model 22: the Model 25A
19-inch Rack Adapter, the Model 28A
Panel Adapter, or custom. The Model 25A
19-inch Rack Adapter allows the rapid
installation of a Model 22 and a Model 11A
gooseneck microphone in a single rack
space. Refer to Figure 2 for details on how
the Model 22 is physically positioned in

Issue 7, November 2001 Model 2 User Guide
Page 16 Studio Technologies, Inc.

the rack adapter. Plenty of room remains
on the right side of the rack adapter,
allowing you to add custom switches,
lights, or jacks as your installation may
require.

The Model 28A Panel Adapter allows the
installation of a Model 22 and a Model 11A
gooseneck microphone in a “cut out”
made in a desk, console, or other enclo­sure. Refer to Figure 3 for a mechanical
drawing of the panel adapter and the
required mounting hole size.

A custom Model 22 installation is any
installation where you devise the mounting
method! Refer to Figure 4 for a mechani­cal drawing showing the dimensions of
the Model 22. This will assist you in imple­menting your own mounting method.

Contained on both the Model 2 and the
Model 22 are standard 9-pin D-type fe­male connectors. A “straight through”
cabling scheme links the units together,
with pin 1 connected to pin 1, pin 2 to pin
2, etc. Shielded cable is required as the
two audio buses linking the Model 22s to
the Model 2 are unbalanced. The shield
should be connected to pin 1 on the 9-pin
plugs. For reference, the following chart
displays the signals associated with the
access station connector:

Pin # Function

1 Common/Shield
2 Interrupt Audio, CH1
3 Interrupt Audio, CH2
4 +18Vdc
5 Interrupt Control, CH1
6 Interrupt Control, CH2
7 Lamp Voltage, CH1
8 Lamp Voltage, CH2
9 Monitor Speaker Mute Control

For ease of installation, each Model 22
contains two 9-pin D-type female connec­tors wired in parallel. This allows signals
to be easily “looped through” on their
way to the next Model 22. For short cable
runs, standard 9-pin video monitor exten­sion cables, commonly used with personal
computers, are an inexpensive and readily
available way to link a Model 2 with a
Model 22. Ensure that any cable assem­blies you purchase use shielded cable,
with the shield connected at pin 1 of
both plugs.

For best performance, a maximum total
cable length of 500 feet should be used to
link Model 22s to the Model 2. Minimizing
the cable length reduces the total exposure
the unbalanced audio buses have to noise
pickup, etc. Cable runs longer than 500
feet are possible but should be carefully
checked for correct operation.

The Model 22 Access Station contains
several configuration switches that must
be set. The input select switch allows the
unit to be set for a mic or a line-level input.
In most cases the Model 11 gooseneck
microphone, available from Studio Tech­nologies, will be used with a Model 22.
Setting the switch to the mic position
activates the mic input terminals. The mic
input is configured only for use with unbal­anced electret-type microphones. The +
terminal on the mic input provides current
limited 5Vdc to power the electret micro­phone. Don’t use a dynamic microphone
as damage may occur. The – terminal is
connected to the microphone’s low signal
lead. The connection marked SHLD is
intended for the shield wire of the micro­phone cable; it doesn’t carry signal.

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 17

The Model 11A Gooseneck Microphone
is an unbalanced electret type, requiring
an external source of DC power. The
microphone utilizes a 3-conductor ¼-inch
plug for interconnection. The tip lead
brings DC power to the microphone, as
well as having microphone audio superim­posed on it. The ring lead is microphone
common. The sleeve lead is a shield
connection.

Included with the Model 11A is a mounting
hardware kit. Included with the kit is a
3-conductor ¼-inch jack used to mate
with the microphone’s plug. At the factory
a 3-conductor wiring harness assembly
is attached to the jack. The wiring harness
has a red-colored wire, a black-colored
wire, and a shield wire. One end of the red
wire is attached to the tip connection on
the jack. The other end should be con­nected to the + terminal on the Model
22’s microphone input. One end of the
black-colored wire is attached to the ring
lead of the jack. The other end should be
connected to the – terminal on the Model
22’s microphone input. One end of the
shield connection is attached to the sleeve
of the jack. The other end should be
connected to the SHLD terminal on the
Model 22’s microphone input.

Setting the input select switch to the
line position activates the line input, and
the associated input trim potentiometer.
The line input circuit is electronically
balanced, capacitor coupled, with an
input impedance of 24k ohms. Balanced
or unbalanced signals can be connected.
The input trim pot allows signals with a
nominal level of –15 to +10dBu to be
correctly interfaced. When connecting
balanced signals the audio should con­nect to the + and – terminals. The shield
wire can be connected to the SHLD

terminal associated with the mic input.
Unbalanced signals require a bit more
attention for correct operation. The signal
high lead should be connected to the +
terminal. The signal low/shield wire should
connect to both the – terminal and the
SHLD terminal. Failure to make this con­nection can result is large amounts of hum
being induced into the interrupt signal.

If you have connected a signal to the line
input terminals, set the trim pot only after
installing the entire IFB system. Refer to
the Technical Notes section of this guide
for details on setting the trim pot.

The Model 22 contains a monitor mute
function, which is intended to prevent
acoustical feedback if the access station
is located close to the monitor loud­speaker associated with the Model 2
Central Controller. When the monitor mute
switch is set to the ON position, the moni­tor output is muted whenever an interrupt
occurs from that access station.

Monitor Output

The Model 2 contains a 4 watt monitor
amplifier which is intended to drive a
small, efficient loudspeaker. A switch on
the front panel selects whether IFB chan­nel 1 or 2 will be monitored. The monitor
output is accessible from the back panel
using a ¼-inch 2-connector jack. The
output can drive 8 ohm or greater loads,
and is quite “hi-fi.” Ensure that both con­ductors of the speaker wiring are “floating”
(isolated) from ground. This will prevent
ground loops that could cause oscillation
or other strange audio gyrations. We
recommend using a good quality loud­speaker. If you do so we think you’ll find
the monitor output sounds quite nice. In
our lab, we tested the monitor amp by
connecting it to a JBL three-way speaker

Issue 7, November 2001 Model 2 User Guide
Page 18 Studio Technologies, Inc.

cabinet, with a compact disc acting as our
program source. The amp, within reason,
really “kicked some tail!”

Connecting AC Mains Power

The Model 2 is factory configured to
operate from AC mains power of either
120 or 220/240V, 50/60Hz. In most cases,
units shipped to North America are factory
selected for 120V operation and are sup­plied with an internal 0.5A, 5 x 20mm fast­acting fuse. Most units shipped outside
North America are factory selected for
220/240V operation and are supplied
with a 0.25A, 5 x 20mm fast-acting fuse.
Before connecting the Model 2 to mains
power, determine the actual mains voltage
and confirm that the Model 2 has been
configured correctly, as an incorrect
setting could seriously damage the unit.
Should it be necessary to change the
unit’s operating voltage refer to the Tech­nical Notes section of this guide. Because
the Model 2 contains no power switch it
will start operating as soon as mains
power is connected.

The Model 2 uses an IEC standard con­nector to mate with the AC mains cord.
Normally the cord supplied has a North
American standard plug at one end and
an IEC connector at the other. In non­North American applications the appropri­ate plug must be attached. The wire colors
in the mains cord, in most cases, will
conform to the internationally recognized
CEE color code and should be wired
accordingly:

Connection Wire Color

Neutral (N) Light Blue
Live (L) Brown
Earth/Ground (E) Green/Yellow

Operation

The Model 2’s Front-Panel
Controls and Indicators

If you value equipment by the number
of switches and lights per rack space,
the Model 2 is really a good deal—there
is more stuff crammed onto the front panel
than we thought possible! Seriously, the
designers had the difficult problem of
getting maximum functionality into a
single rack space. We had heated argu­ments about the feature list, what to in­clude, what to delete. In the end, we feel
that all important features were included.
Once you understand all the functions, we
think you’ll find the Model 2 quite power­ful, yet easy and intuitive to use.

Looking at the Model 2’s front panel from
the left to the right, you should note the
functional groups: internal interrupt micro­phone, channel 1-related items, channel
2-related items, voice activated (VOX)
interrupt, telephone interface 1, telephone
interface 2, monitor amplifier, and power
LED. We’ll discuss these groups in the
following sections.

Internal Interrupt Microphone

The Model 2 contains an internal micro­phone which can be used to access
either, or both, of the IFB channels. Two
momentary action push button switches
are located on the left end of the front
panel and are labeled IFB 1 and 2. Press­ing either switch mutes (or optionally
dims) program audio, mutes the monitor
speaker output, and connects the micro­phone to the selected IFB channel(s). The
IFB status LED associated with each chan­nel will light whenever its corresponding
interrupt button is pressed. Notice that

Model 2 User Guide Issue 7, November 2001
Studio Technologies, Inc. Page 19