Studio Technologies Gen II User Manual

Model 2 Central Controller
and Related Components
User Guide
This User Guide is applicable for Model 2 serial numbers:
M2-01361 and later
© 2005 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50131-1205, Issue 8
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Table of Contents
Introduction .......................................................................................... 5
What This User Guide Covers ........................................................ 5
Model 2 Central Controller .............................................................. 6
Model 22 Access Station ................................................................. 8
Model 32 & Model 33 Talent Amplifiers ........................................... 8
Installation ............................................................................................. 9
Locating the Unit ............................................................................. 10
Mounting ......................................................................................... 10
Program Inputs ............................................................................... 10
Auxiliary Audio Input ....................................................................... 10
Talent Amplifier Output ................................................................... 11
Line Outputs .................................................................................... 11
Connecting Telephone Lines .......................................................... 12
Access Stations ............................................................................ 13
Monitor Output .............................................................................. 15
Connecting AC Mains Power ........................................................ 15
Operation ............................................................................................ 16
The Model 2’s Front-Panel Controls and Indicators ..................... 16
It’s Time to Use the System! ......................................................... 19
Technical Notes ................................................................................... 20
Circuit Descriptions ............................................................................. 24
Model 2 Central Controller ............................................................ 25
Model 22 Access Station .............................................................. 32
Model 32 Talent Amplifier ............................................................. 34
Model 33 Talent Amplifier ............................................................. 35
Troubleshooting .................................................................................. 36
Model 2 Central Controller ............................................................ 36
Model 22, Model 32, & Model 33 ................................................. 37
Specifications ...................................................................................... 38
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,
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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
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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.
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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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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.
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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
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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
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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
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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
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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:
Pin # Function
1 Common/Shield 2 Interrupt Audio, CH1 3 Interrupt Audio, CH2 4 +18 Vdc 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
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
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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
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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.
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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
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