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 8, December 2005 Model 2 User Guide
Page 4 Studio Technologies, Inc.
Introduction
The IFB Plus Series Model 2 Central Controller from Studio Technologies is a highly
integrated, 2-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
M2-01361 and later. If you are installing a
Model 2 with a serial number of M2-01360 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.
Schematic diagrams are available upon
request.
The following items will be covered in this
User Guide:
among many other features. The unit is
powered by 120 or 220/240 V, 50/60 Hz.
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 pushbutton
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.”
Model 2 Central Controller
An integrated 2-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,
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 5
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.
Model 2 Central Controller
Contained in a single rack space unit is everything required to implement a 2-channel
IFB system. Features include multiple program inputs, telephone interfaces, voiceoperated (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 220/240 V (factory
configured), 50/60 Hz 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 incoming 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 +22 Vdc
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 XLRtype connectors on the back panel. The program inputs are electronically balanced with
a nominal input impedance of 24 k 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
+4 dBu input level to be adjusted over a
±8 dB range.
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 Circuits
Each IFB channel contains a studioquality compressor circuit. This serves to
even out variations in the interrupt audio signals and smoothly control peak signal levels. They make talent cues more intelligible
Issue 8, December 2005 Model 2 User Guide
Page 6 Studio Technologies, Inc.
and prevent abnormally high signal levels
from reaching a user’s ears. The resulting
audio quality is very, very good.
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 telephoneline mode or the standard-audio mode. A
telephone line has the profile of being a
2-wire, DC-biased (normally –48 Vdc) 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.
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 currentspecific 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.
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 7
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 3-position 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 voiceactivated 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 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 pushbutton
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 line-level 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.
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Page 8 Studio Technologies, Inc.
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.”
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 220/240 V, depend ing on the shipping destination. It may
need to be revised for your installation.
• 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.
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.
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 9
Locating the Unit
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 rack space. It
weighs a bit over 10 pounds (4.7 kg), and
operates on either 120 or 220/240 V, 50/60
Hz. 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 +4 dBu. A trim potentiometer is associated with each input, giving a ±8 dB 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 24 k ohms. 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 +4 dBu. A trim pot is associated with the auxiliary input, giving a ±8 dB
adjustment range. The pot is not intended
for precise calibration, but strictly to allow
Issue 8, December 2005 Model 2 User Guide
Page 10 Studio Technologies, Inc.
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.
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 24 k ohms.
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 +22 Vdc 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 linelevel output with a nominal signal level of
+4 dBu. 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 XLR-type 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 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 11
Model 2’s sonic quality is as good as many
audio consoles, tape recorders, etc. As an
example, the frequency response from program input to line output is better than
±0.5 dB from 20 Hz to 20 kHz. 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 ±8 dB 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 ±8 dB receive level trim pot
• Switch allows manual off-hook and
hang-up (telephone line mode)
• Operating mode and loop current status
LEDs
Setting the mode switches and connecting signals is quite easy. Set the telephone
Issue 8, December 2005 Model 2 User Guide
Page 12 Studio Technologies, Inc.
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 (RJ11-type) 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 tele-phone 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 unterminat-ed
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 +4 dBu professional audio
standard. The nominal receive signal level is
expected to be –15 dBu, the transmit level
is –6 dBu. Trim pots are associated with
both interfaces, allowing the receive level
to be adjusted over a ±8 dB range. Special
precautions may need to be taken when an
interface is set for standard audio mode and
+4 dBu 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
pushbutton 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 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
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 13
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.
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.
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:
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
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 5 Vdc 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.
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
Issue 8, December 2005 Model 2 User Guide
Page 14 Studio Technologies, Inc.
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 24 k ohms. Balanced or unbalanced
signals can be connected. The input trim
pot allows signals with a nominal level of
–15 to +10 dBu 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
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 220/240 V, 50/60 Hz. In most cases,
units shipped to North America are factory
selected for 120 V operation and are supplied with an internal 0.500 A, 5 x 20 mm
fast-acting fuse. Most units shipped outside North America are factory selected for
220/240 V operation and are supplied with a
0.250 A, 5 x 20 mm 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
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 15
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 non-North 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
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 pushbutton 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 chan-nel will light whenever its
corresponding interrupt button is pressed.
Notice that sound enters the microphone via
the small openings in the front panel above
and slightly to the right of the switches.
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.
Issue 8, December 2005 Model 2 User Guide
Page 16 Studio Technologies, Inc.
Program Select, Level Adjustment, and
Indicators
Two identical sets of controls and indicators
serve IFB channels 1 and 2. Each channel
contains six program select switches, two
status LEDs, a program level control, and a
5-segment LED level meter. The six switches
are used to select which of the four program
inputs, and the receive audio from the two
telephone interfaces, will serve as the program audio source(s). The switches were
chosen to allow more than one source to be
selected at a time. The ability to simultaneously depress and lock multiple buttons is
not a defect, but is a feature which can be
useful in special circumstances.
The red LED, labeled IFB, is lit any time program audio is being interrupted. There are
three ways an interrupt can take place: by
the internal microphone being activated, by
a Model 22 Access Station being used, or
via a control signal from the voice operated
(VOX) interrupt function. The yellow LED,
labeled VOX, is lit any time interrupt is
caused by the VOX function.
The program level control allows the program audio signal to be adjusted relative to
the interrupt audio level. The interrupt level
is internally fixed and serves as the reference. The gain structure was configured
so that the level control set for 50 percent
of rotation (12 o’clock) will give a program
level approximately equal to the interrupt
level. This statement is made under the assumption that a +4 dBu program signal is
selected and its associated input trim pot is
correctly set.
The 5-segment LED level meter displays the
internal level of the composite (program and
interrupt) IFB signal. The three green LEDs
are lit with signals in the normal operating
range. The yellow LED lights with a signal
slightly higher than average. The red LED
lights when signal levels are in the “headroom” area. The ballistics of the meter are
a cross between that of a VU meter and a
peak (PPM) meter. (We affectionately refer to
it as a “PU” meter!) The meter should prove
useful during installation and maintenance,
as well as during normal operation.
A typical interrupt signal will light the green
LEDs, with peaks lighting the yellow LED.
The internal compressor circuits will keep
most interrupt signals from lighting the red
LED. When an interrupt is not taking place,
the level meter will reflect the level of the
program audio source. Setting the program
level control to occasionally light the yellow
LED will give a program level approximately
equal to the interrupt level.
Voice Operated (VOX) Interrupt
The Model 2 contains a specialized function
that allows an audio signal to automatically
interrupt the program signal. By contrast,
using the Model 2’s internal microphone
requires an explicit action by the operator,
i.e., pressing a button to cause an interrupt.
In some cases, this explicit action is simply
not possible. An example would be a director giving cues via a two-way radio or a
telephone line. The VOX circuitry creates an
interrupt control signal by detecting energy
in the voice band. This control signal acts
on the selected IFB channel, interrupting
program audio and routing VOX audio in its
place. The VOX interrupt can be assigned
to either IFB channel 1 or 2, but not to both
simultaneously.
The VOX interrupt function is only sophisticated from an internal-circuitry stand point.
Operation is quite simple, with only two
switches to set. The input switch allows one
of three audio sources to be connected to
the VOX input: audio from the auxiliary audio
input, receive audio from telephone interface
1, or receive audio from telephone interface 2. The output switch is used to select
whether the VOX interrupt function is off (not
used), or is assigned to interrupt IFB channel 1 or 2. VOX operation can commence
as soon as the output is assigned to one of
the channels. VOX interrupt activity can be
noted by observing the yellow VOX LED associated with the assigned IFB channel.
Telephone Interface 1
Two status LEDs, one switch, and one trim
potentiometer are associated with telephone
interface 1. The yellow LED, labeled STD, is
lit whenever the interface is set for the standard audio mode by the switch on the back
Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 17
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