Studio Technologies IFB Plus Series User manual

Copyright © 2015 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50142-0315, Issue 2
User Guide
Issue 2, March 2015
This User Guide is applicable for serial numbers
M2A-03451 and later

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Model 2A User Guide Issue 2, March 2015
Studio Technologies, Inc. Page 3
Table of Contents
Revision History ........................................................... 4
Introduction ................................................................... 5
Installation .................................................................... 12
Operation ...................................................................... 24
Configuration ................................................................ 29
Technical Notes ............................................................ 31
Specifications ............................................................... 33
Appendix A–IFB Plus Series Mechanical Drawings ..... 37
Appendix B–IFB Plus Series Optional Accessories ...... 42

Issue 2, March 2015 Model 2A User Guide
Page 4 Studio Technologies, Inc.
Revision History
Issue 2, March 2015:
1. Documented revised telco interface new capabilities and connection details:
- Added the ability to connect both sources using jack 1.
- Also added switched output connections.
Issue 1, October 2013:
1. Initial release.

Model 2A User Guide Issue 2, March 2015
Studio Technologies, Inc. Page 5
Introduction
The IFB Plus Series Model 2A Central Con-
troller from Studio Technologies is a highly
integrated, 2-channel IFB (interruptible fold-
back) unit. It is the main component of the
IFB Plus Series which is expressly designed
to provide talent cueing for ENG, SNG, OB,
and mobile production facilities. It can also
find use in fixed installations that need a
compact but feature-rich stand-alone IFB
system. The performance and features of
the Model 2A, along with its companion
accessories, reflect the needs of contem-
porary applications. Only after extensive
polling of field production and engineering
personnel was the Model 2A’s feature group
established. We think you’ll find it to be a
great addition to your facility.
What This User Guide Covers
This guide is designed to assist you when
installing, configuring, and using the Model
2A Central Controller and related accesso-
ries. The following items will be covered in
this User Guide:
Model 2A Central Controller
The Model 2A Central Controller is an inte-
grated 2-channel IFB unit intended for ap-
plications 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 space
(1U) of a 19-inch rack enclosure. The unit’s
resources include multiple program inputs,
integral telephone interfaces, monitor ampli-
fier output, internal interrupt microphone,
and support for additional talk locations.
The unit’s power input can range from 100
to 240 volts, 50/60 hertz. This “universal
input” ensures correct operation virtually
anywhere in the world.
Model 22 Access Station
The Model 22 Access Station is used by a
producer or director to access the Model
2A’s two IFB channels. It allows connec-
tion of a Studio Technologies’ Model 11A
Gooseneck Microphone or a line-level audio
source. The unit contains two lighted push-
button switches which display IFB interrupt
status. Up to four Model 22 units can be
connected to and powered by a Model 2A
Central Controller. The Model 25A 19-Inch
Rack Adapter allows a Model 22 Access
Station and Model 11A Gooseneck Micro-
phone to be mounted in a single space (1U)
of a standard 19-inch rack. 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. The Models 11A, 22, 25A, and
28A are purchased separately.
Figure 1. Model 2A Central Controller Front and Back Views

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Model 24 Access Station
The Model 24 Access Station allows broad-
cast personnel to access the four IFB chan-
nels associated with two Model 2A units.
The Model 24 contains five lighted pushbut-
ton switches, four of which are used to ac-
tivate and display the status of the four IFB
channels and one that provides an “all call”
function. The Studio Technologies’ Model
11A Gooseneck Microphone or a line-level
audio source can be connected. Up to four
Model 24 units can be connected and sup-
ported by two Model 2A units. The Model
27A 19-Inch Rack Adapter allows a Model
24 and a Model 11A Gooseneck Micro-
phone to be mounted in a single space of
a 19-inch rack enclosure. The Models 11A,
24, and 27A are purchased separately.
Model 32A and Model 33A Talent
Amplifiers
The Model 32A and Model 33A Talent
Amplifiers are self-contained “beltpack”
units that support connection of talent ear-
pieces or headsets. Purchased separately,
a total of up to six of these talent amplifiers
can be connected to, and powered by, a
single Model 2A Central Controller.
The Model 32A is intended for use by on-
air and production support personnel. It
connects to the Model 2A’s talent amplifier
output by way of a standard audio cable
that uses 3-pin XLR connectors. A “loop
through” 3-pin XLR connector is provided
on the Model 32A for easy interconnection
with additional talent amplifier units. The
Model 32A contains a power active LED
indicator light and 2-position source
switch, along with an output level control.
For user convenience, both ¼-inch and
3.5 mm monaural output jacks are provid-
ed. Either IFB channel 1 or 2 can be
selected, amplified, and sent to the output
jacks with the level adjusted as desired.
The Model 33A is similar to the Model 32A
but allows creation of a “mix” of IFB chan-
nels 1 and 2. Two level controls, along with
a source select switch, allows camera and
production personnel to hear cues from
either or both IFB channels. This allows
IFB signals intended for support person-
nel and on-air talent to be simultaneously
monitored. For user convenience, ¼-inch
and 3.5 mm monaural output jacks are
provided.
Model 2A Central Controller
Mounted in a single space of a 19-inch
rack, the Model 2A provides everything
required to implement a 2-channel IFB
system. Features include multiple program
inputs, telephone interfaces, voice-oper-
ated (VOX) interrupt, level meters, monitor
amplifier output, and an internal interrupt
microphone. In addition, up to four Model
22 or Model 24 Access Stations can be
connected to a Model 2A, allowing pro-
ducer or director positions to access the
IFB channels. In addition, up to six Model
32A or Model 33A Talent Amplifiers can be
connected to a Model 2A. These portable
“beltpack” units interconnect with a Model
2A using standard microphone cables.
Both DC power and two channels of audio
are supplied on just one 3-conductor ca-
ble, providing personnel with convenient,
reliable access to the two IFB channels.
The Model 2A packs numerous features
into a rugged yet lightweight single-rack-
space (1U) enclosure. Standard con-
nectors are used throughout, including
3-pin XLR, ¼-inch 2-conductor, 9-position
D-subminiature, and modular telephone
(RJ11) jacks. A source of 100-240 volts,

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Studio Technologies, Inc. Page 7
50/60 hertz is connected via a detachable
mains cord and provides power for the
Model 2A.
IFB Channels
The Model 2A contains two independent
IFB channels. Each channel has individual
controls and indicators, including program
source select switches, program level con-
trol, 5-segment LED level meter, and LED
status indicators. The features of one of
two identical channels will be highlighted
in this paragraph. Six switches allow the
four program audio inputs and audio com-
ing from the two telephone interfaces to
be selected as program audio sources. A
rotary level control allows adjustment of
the program audio level relative to that of
the non-adjustable interrupt audio level. A
5-segment LED meter displays the level of
the composite IFB audio signal. (The com-
posite audio signal is the combination of
the selected program audio source(s) and
the interrupt audio source(s).) The level
meter facilitates the rapid setting of the
program level control, as well as providing
a general indication of the IFB channel’s
signal level.
Each channel’s composite IFB audio signal
(a mix of program and interrupt audio)
is sent to four places: a line-level output,
the talent amplifier output, telephone in-
terface 2, and the monitor output section.
Each line output provides an electronically
balanced, line-level signal that interfaces
with external equipment via a 3-pin XLR
connector. The talent amplifier output
provides IFB channel 1 and 2 audio, along
with 24 volts DC power on one 3-pin XLR
connector. Any combination of up to six
Model 32A or Model 33A units can be con-
nected to the talent amplifier output. For
application flexibility, the talent amplifier
output provides 200 ohm line impedances
on both of its output channels. This allows
direct connection of not just listen-only
devices, such as the Models 32A and 33A,
but party-line (PL) user beltpacks as well.
In this way popular PL beltpacks, from
suppliers such RTS® and Clear-Com®,
can be connected and used to create a
small PL intercom system that includes IFB
listen. A selector switch associated with
telephone interface 2 can be used by an
operator to send either IFB channel 1 or 2
out the connected phone line. The monitor
output section allows loudspeaker moni-
toring of audio from either IFB channel 1
or 2. (An optional external loudspeaker is
required.)
Program Inputs
The Model 2A contains four line-level
program inputs. Each can be individu-
ally 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 3-pin XLR connec-
tors located on the unit’s back panel. The
program inputs are electronically balanced
and feature low noise, low distortion, and
high common mode signal rejection. Each
program input has a trim potentiometer as-
sociated with it. The trim pots, accessible
from the back panel, allow source signals
with a nominal level of –10 to +8 dBu to be
correctly utilized.
Program audio is muted whenever inter-
rupt activity is taking place. Solid-state
circuitry is used to provide noise-free audio
switching with essentially no “clicks” or
“pops” added. If desired, a program “dim”
rather than a full mute can be implemented
by adding two resistors to the Model 2A’s
circuit board.

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Compressor Circuits
The two IFB channels contain studio-quality
compressor circuitry to control the dynamic
range of the interrupt audio. These play an
important role in how the Model 2A main-
tains high audio quality, specifically evening
out level variations presented by the talk
signals associated with various IFB users.
The compressors make talent cues more
intelligible and prevent abnormally high
signal levels from reaching user’s ears. The
resulting audio quality is very, very good.
Telephone Interfaces
The Model 2A contains two telephone
interfaces. Both interfaces can be used
to bring audio into the Model 2A 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 audio source for the
voice operated (VOX) interrupt function.
Each telephone interface has a receive-lev-
el trim potentiometer that is accessible via
a small hole in the front panel. The large
level variations that can be presented by a
telephone line can make “on the fly” level
trimming a useful feature. In addition to re-
ceiving audio, telephone interface 2 can be
used to originate an IFB “feed” (IFB output).
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 telephone interfaces contain a unique
feature which allows two very different
types of telephone “lines” to be correctly
interfaced. Each interface can be indepen-
dently set to operate in either a telephone
line mode or a standard audio mode. A
telephone line has the profile of being a 2-
wire, DC-biased (normally –48 volts) circuit
provided by a local telephone company,
long-distance carrier, or private telephone
system. A standard audio signal could be
provided by, for example, a “dry” (no DC
voltage provided) fax adapter associated
with a cellular telephone.
When an interface is set to the telephone
line mode and a telephone line with DC
voltage is connected, full monitoring and
control is implemented. Each interface con-
tains a switch that allows the telephone line
to be answered (taken “off hook”) or hung
up (placed “on hook”). DC loop current is
monitored when the interface is active (off
hook). If a telco-provided disconnect signal
(a momentary break in loop current) is de-
tected the interface will automatically return
to its idle (on-hook) state. Telephone inter-
face 1 contains an LED status indicator that
lights whenever loop current is detected.
Telephone interface 2 has a status LED that
“flashes” when a ringing signal is detected
and lights continuously when loop current
is detected. Interface 2 also implements an
auto answer function which can automati-
cally take the telephone line to the answer
(off-hook) state when a ringing signal is
detected.
In many cases a “telephone line” in a mo-
bile broadcast application is actually pro-
vided by a cellular telephone. This cellular
telephone may provide a “dry” (no DC loop
current) audio output signal. The standard
audio mode was designed expressly to
interface with this “cell phone” arrange-
ment. In this mode, the interface’s loop
current-specific features are disabled, and
the interface appears electrically as a trans-
former-coupled balanced audio interface.
When an interface has been set for the
standard audio mode its front-panel line
status switch is inactive as is its loop status
LED. Also inactive in the standard audio

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switches, allowing the internal microphone
to interrupt IFB channel 1, channel 2, or
both channels 1 and 2.
Monitor Output
The Model 2A contains a simple but excel-
lent monitor output section. At the core is
a 4 watt high-performance audio amplifier
designed to drive an 8 ohm (or greater)
loudspeaker. (The speaker is optional
and is provided as part of an installation.)
Associated with the monitor output are a
3-position source select switch and a level
control. The switch selects whether IFB
channel 1 or IFB channel 2 will be moni-
tored, as well as having an off position. A
click-free circuit mutes the monitor output
whenever the internal microphone or a
Model 22 or Model 24 Access Station is
interrupting either IFB channel.
Model 22 Access Station
The Model 22 Access Station and related
accessories (all purchased separately)
provides the capability for adding up to
four additional interrupt locations. Model
22 units are intended to be installed at
positions convenient to producers, direc-
tors, 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.
mode is telephone interface 2’s auto an-
swer function. An LED associated with
each telephone interface displays when
the standard audio mode is selected.
Voice Operated (VOX) Interrupt
The Model 2A contains circuitry to allow
an audio signal to serve as both an inter-
rupt audio source and a control signal.
This eliminates the need for a separate
push-to-talk button or contact closure. The
VOX feature allows an audio signal from
a remote source, such as a 2-way radio
or telephone line, to serve as the interrupt
source. The VOX function was optimized
for detecting audio signals in the voice
band. As voice detection is not a trivial
task, great care was taken when designing
the circuitry to support this function.
Three signals can serve as the audio
source for the VOX interrupt function:
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 is only associated with the VOX
interrupt function. A 3-position switch se-
lects which source will be used. A second
3-position switch is used to select which
IFB channel is to respond to the VOX inter-
rupt function. The VOX interrupt function
can be assigned to only one IFB channel
at a time or it can be disabled. Each IFB
channel contains an LED indicator light
to display when a VOX (voice-activated)
interrupt is taking place.
Internal Interrupt Microphone
Contained behind the Model 2A’s front
panel is an internal interrupt microphone.
Associated with the microphone are two Figure 2. Model 22 Access Station Front View

Issue 2, March 2015 Model 2A User Guide
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The two high-quality backlit pushbutton
switches provide access to the Model 2A’s
two IFB channels. The lights in the switch-
es display when an interrupt is taking place
on its respective channel; lighting brightly
when IFB is active and dim when IFB is
idle. An input select switch allows con-
nection of a Model 11A Gooseneck Micro-
phone or external line-level signal source.
The electronically balanced line-level input
allows interfacing with other communica-
tions equipment, such as “hot mic” signals
from an intercom user station.
The Model 22 can be configured to mute
the Model 2A’s monitor amplifier output.
This function will prevent acoustic feedback
from occurring when a Model 22 is located
close to the Model 2A’s monitor speaker.
Model 22 Access Stations are linked to the
associated Model 2A Central Controller via
9-pin D-subminiature female connectors.
Each access station contains two connec-
tors, allowing a simple daisy-chain installa-
tion. The nine leads carry all signals; audio,
control, status lamp (tally), and power. The
Model 2A 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 Mi-
crophone in one space (1U) of a standard
19-inch rack. The Model 28A Panel Adapter
allows a Model 22 and a Model 11A Goose-
neck Microphone to be mounted in a panel
opening. Refer to Appendix B for details on
these optional accessories.
Model 24 Access Station
The Model 24 is similar to the Model 22
with the exception that it works with two
Model 2A units. In this way production
personnel can access all four of the IFB
channels associated with the two Model
2A units. Up to four Model 24s can be con-
nected to each Model 2A. A Model 24 unit
consists of a metal chassis that holds five
lighted pushbutton switches, audio and
control circuitry, and microphone and line
input connectors.
Figure 3. Model 22 Access Station shown mounted in optional Model 25A 19-Inch Rack Adapter with
optional Model 11A Gooseneck Microphone
Each of the four IFB channel pushbutton
switches display when an interrupt is taking
place on its respective channel. A fifth but-
ton is specified as “all call” and lights when
pressed. The Model 24 supports connec-
tion of an optional Model 11A Gooseneck
Microphone or a line-level signal. The latter
is transformer-balanced, allowing compat-
ibility with virtually any line-level source. A
switch is used to select the interrupt audio
Figure 4. Model 24 Access Station Front View