User Guide Issue Preliminary 2, March 2009 This User Guide is applicable for serial numbers M45-00151 and later Copyright © 2009 by Studio Technologies, Inc., all rights reserved www.studio-tech.
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Table of Contents Introduction ................................................................... 5 Installation ..................................................................... 10 Configuration ................................................................ 16 Operation ...................................................................... 19 Technical Notes ............................................................. 24 Specifications ...............................................................
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Introduction The Model 45 is designed to interface 2-wire full-duplex party-line (PL) intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Applications for the Model 45 include television sports and live-event broadcasting, theme park and theater installations, corporate AV, and industrial testing environments. The unit provides one full-featured twochannel 2-wire-to-4-wire interface. The interface features hybrid circuitry that includes automatic nulling capability.
2-Wire Party-Line Interface The Model 45’s two-channel 2-wire partyline interface is optimized for direct connection with a dual-channel party-line intercom circuit. In addition, single-channel partyline intercom circuits can also be connected. Many broadcast applications use the dual-channel TW-series from RTS®, which includes their popular BP325 belt pack. The Model 45’s 2-wire interface is configured for a –10 dBu nominal level, exactly matching the level of the TW-series.
of its 2-wire-to-4-wire hybrid circuits. Each of the two independent circuits provides low noise and distortion, good frequency response, and high return-loss (“nulling”), even when presented with a wide range of 2-wire party-line conditions. Unlike telephone-line (“POTS”) oriented DSP-based hybrid circuits, the Model 45’s analog circuitry provides extended frequency response.
of only 2 dB is required. The RTS ADAM™ series of matrix intercom systems has a nominal level of +8 dBu. This level also applies to their RVON-I/O VoIP products. As such, reducing their nominal input and output levels by 4 dB will ensure optimal compatibility. The Model 45 contains four 5-segment LED level meters with two displaying the level of the signals being received on the 4-wire inputs and two displaying the level being sent out the 4-wire outputs.
audio quality, advanced users might need to disable it. This would allow full control over the Model 45’s two hybrid circuits, enabling them to be used in a completely independent manner. Simple Installation The Model 45 uses standard 3-pin XLRtype connectors, allowing convenient 2-wire party-line and 4-wire interconnection in broadcast and general audio environments. For flexibility, access to the 2-wire party-line intercom interface can be made using either a male or female XLR connector.
The next step was to identify resources that would improve the installation process and make operation more reliable. This led to the use of standard 3-pin XLR-type audio connectors, enabling rapid installation and troubleshooting in any locale. The inclusion of LED level meters allowed continuous monitoring of the input and output signals. Additional status LEDs were also deemed to be valuable. Configuration DIP switches would allow crucial operating modes to be selected.
cables will help to ensure more reliable and consistent intercom system performance. The differential (“balanced”) 4-wire circuits are typically not impacted by the length of their interconnecting cables. A final location criterion is to provide access to the Model 45’s front panel. An optimal location will allow convenient use of the auto null pushbutton and easy observation of the level meters and status LEDs.
Once the desired one or two Model 45 units have been installed in a rack-mount front panel, the assembly can be mounted into the designated equipment rack. One space (“1U” or 1.75 vertical inches) in a standard 19-inch equipment rack is required. Secure the unit into the equipment rack using two mounting screws per side. 4-Wire Audio Inputs and Outputs Two audio line input and two audio line output signals are associated with the 4-wire interface section of the Model 45.
unbalanced source in this manner results in hum or noise, connect XLR pin 2 to high (+ or hot) and pin 3 to shield; leave pin 1 unterminated. 4-Wire Line Outputs The Model 45’s dual-channel interface provides two analog line-level audio outputs. These outputs are intended to be connected to inputs on the devices associated with the 4-wire audio signals. The outputs are capacitor coupled, transformer balanced with a nominal level of +4 dBu.
pin 3 of the Model 45’s 2-wire party-line intercom interface, will be utilized. Pin 2, the Model 45’s audio channel 1, will only be used for connecting DC power to the connected devices. While the audio resources provided by channel 1 will not be used, the Model 45 can still be used to supply DC power on pin 2. As previously mentioned, the maximum current draw on the 30 volt DC output is 300 milliamperes. Alternatively, an external intercom power supply can support the connected devices.
External 24 Volts as the Power Source As previously discussed, the Model 45 can be powered by a source of 24 volts DC. A “locking” 2.1 x 5.5 mm coaxial power jack is located on the back panel of the unit. The center pin of the jack is the positive (+) connection. While the requirement for the external source is nominally 24 volts, correct operation will take place over a 20 to 28 volt range. The Model 45 requires 750 milliamperes for correct operation.
drop can become appreciable in situations where belt pack operation wouldn’t normally be impacted. Performing accurate calculations in this scenario is a bit more difficult but might be required to ensure a reliable installation. Initial Operation As soon as a source of power is applied the Model 45 will begin its power-up sequence. As a “boot-up” indication the input power, status, and meter LEDs will light, one at a time, in a “walk-through” sequence.
external source of 24 volts is going to be connected switch 1 should be placed in its off (down) position. This ensures that a failure of the connected 24 volt DC source won’t cause the Model 45 to automatically revert to pulling power from the intercom circuit. Some additional details might be helpful. Be certain to allow only the connected intercom circuit to supply power (switch 1 on) if it’s fully able to do so.
interface to be auto nulled at approximately the same time. The dual auto null mode allows a single “tap” of the button to initiate nulling of both hybrid circuits. single-channel intercom circuit are connected to the Model 45. In this latter case only one of the Model 45’s audio channels will be used. When configuration DIP switch 3 is in its on (up) position the independent auto null mode is selected.
the Model 45’s 2-wire-to-4-wire converter circuitry. These audio artifacts will not cause any damage but will be sent out of the 4-wire line outputs. Users of the 4-wire equipment may be less than pleased with what they hear! 4-Wire Mute during Auto Null As part of the auto nulling process audio tones are generated and sent out the 2-wire intercom interfaces. These tones, depending on the nulled state of the hybrid circuits, will also appear on the outputs of the 4-wire interface circuits.
are fully isolated from the 2-wire intercom circuit. In this situation the Model 45’s only function is to route, by way of the hybrids, the 2-wire interface’s audio signals to and from the 4-wire outputs and inputs. In this mode of operation the Model 45 acts as a typical user station on the connected intercom circuit. The author is aware that user intercom devices almost always draw power from pin 2 rather than pin 3.
pin 2 falls below 24 volts for a continuous 1- second interval. The hardware and software responds to this condition by turning off the power source to pin 2 and flashing the pin 2 LED as a warning. After a 5-second “cool-down” interval the output returns to the same condition as upon initial power up. Power is again applied to pin 2, the pin 2 status LED will light, and monitoring won’t begin for another five seconds.
device’s nominal level matches the Model 45’s level setting its actual nominal level may be significantly different. With a digital matrix intercom system this problem could be due to an incorrect configuration having been made to a specific channel or port. For example, the RTS ADAM system has a published nominal level of +8 dBu, but using its configuration software it’s possible to set panels or ports to a level different than nominal.
An auto null sequence begins with the muting of the 4-wire input and output signal paths associated with the channel being nulled. This is followed by a short period of 24 kHz signal that is sent out the 2-wire party-line intercom interface channel. This will turn off microphones on those connected user devices that are compatible with the RTS TW-series “mic kill” protocol. The actual auto nulling process is performed next. A series of tones will be sent out the 2-wire interface.
readily apparent. The front-panel LEDs will continue to display the DC power status of pins 2 and 3. But whether or not either or both LEDs are lit, the Model 45 will never apply 200 ohm terminations to pins 2 or 3. For the hybrid circuits to remain stable termination impedances must be provided by the connected circuits. If these are not present one might find the hybrid circuits generating very unpleasant audible noise.
Major Release Number Release Sub-Number O 4 .4 O O 3 .3 O 2 .2 O 1 .1 O Figure 8. Detail of front panel showing the status LEDs that display the software version. In this example, the software version is 1.3. Note that while it’s easy to determine which software version is loaded into the Model 45 a trip back to the factory is required to update it. The 8-bit microcontroller that provides the unit’s logic “horsepower” also includes internal FLASH memory.
unit. Power can be provided by the connected intercom circuits or by way of an external source of 24 volts DC. The final step to achieve correct performance is for the auto null function on each Model 45 to be activated. Refer to Figure 9 for details. Figure 9. Two Model 45 units connected as a universal 2-wire-to-2-wire bridge Issue Preliminary 2, March 2009 Page 26 Model 45 User Guide Studio Technologies, Inc.
Specifications General Audio: Meters: 4 Function: displays level of 4-wire inputs and outputs Frequency Response: ±2.5 dB 100 Hz to 8 kHz Type: 5-segment LED, modified VU ballistics Distortion (THD+N): <0.
Appendix A Interfacing RTS® Matrix Intercom Systems with the Model 45 Interface ADAM™ Matrix Intercom System Analog Ports to Model 45 Interface RVON-I/O I/O Connections to Model 45 Interface Issue Preliminary 2, March 2009 Page 28 Model 45 User Guide Studio Technologies, Inc.
Appendix B Interfacing Riedel® Artist™ Matrix Intercom System Analog Ports with the Model 45 Interface Model 45 User Guide Studio Technologies, Inc.
Appendix C Interfacing Clear-Com® Matrix Intercom System Analog Ports with the Model 45 Interface Issue Preliminary 2, March 2009 Page 30 Model 45 User Guide Studio Technologies, Inc.
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