User Guide Issue 3, August 2015 This User Guide is applicable for serial numbers M45A-00151 and later Copyright © 2015 by Studio Technologies, Inc., all rights reserved www.studio-tech.
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Table of Contents Revision History ............................................................ 4 Introduction ................................................................... 5 Installation ..................................................................... 10 Configuration ................................................................ 16 Operation ...................................................................... 20 Technical Notes .............................................................
Revision History Issue 5, August 2015: 1. Minor corrections and adds figures for clarity. Issue 2, November 2011: 1. Minor corrections and enhancements. Issue 1, April 2011: 1. Initial release. Issue 3, August 2015 Page 4 Model 45A User Guide Studio Technologies, Inc.
Introduction The Model 45A is designed to interface 2wire full-duplex party-line (PL) intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Applications for the Model 45A include television sports and live-event broadcasting, theme park and theater installations, corporate AV, and industrial testing environments. The unit provides one full-featured two-channel 2-wire-to-4-wire interface. The interface features hybrid circuitry that includes automatic nulling capability.
2-Wire Party-Line Interface The Model 45A’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 BP-325 beltpack. The Model 45A’s 2-wire interface is configured for a –10 dBu nominal level, exactly matching the level of the TW-series.
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 45A’s analog circuitry provides extended frequency response. With a pass band of 100 Hz on the low end and 8 kHz on the high end natural-sounding voice signals can be sent to, and received from, the 2-wire party-line circuit.
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 45A 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. During installation and setup the meters are invaluable in helping to confirm that proper operation is taking place.
Simple Installation The Model 45A uses standard 3-pin XLR 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 on the back panel or a male XLR connector on the front panel. In many applications the Model 45A will be powered by an external source of 24 volts DC.
the use of standard 3-pin XLR 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.
length of their interconnecting cables. A final location criterion is to provide access to the Model 45A’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. Protecting the Enclosure The Model 45A is shipped as a selfcontained unit suitable for portable use. Installed on the bottom of the chassis are screw-on “bump on” protectors.
front of the rack panel using the two 4-40 Philips-head screws. Attach the 3-position socket to the 3-pin header located on the main printed circuit board adjacent to the back panel. Ensure that the three pins of the header align with the three openings in the socket. Reattach the top panel, securing it to the chassis with the four screws and lock washers. If required for mounting clearance, remove the “bump on” protectors from the bottom of the chassis.
Figure 4. Detail of back panel showing line inputs and outputs 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 45A’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.
Dual-Channel Intercom Systems If compatibility with RTS TW-series is desired the mating connector (one male or one female) should be wired so that common is on pin 1, DC with channel 1 audio is on pin 2, and channel 2 audio is on pin 3. This wiring scheme applies whether the connected devices are to be powered by an external source or by the Model 45A’s internal 2-wire intercom power source.
Model 45A Power Source The Model 45A requires power for operation of its internal circuitry. This can be provided by an external source of 24 volts DC or by way of the connected 2-wire party-line circuit. As you might expect, if the Model 45A is to serve as the 2-wire party-line power source an external source of 24 volts DC must be connected. When a 24 volt DC power source is connected it always takes priority.
45A’s 2-wire (PL) connectors. Whether the connected party-line intercom circuit can provide this much energy will depend on the characteristics of a specific installation. The relevant factors include the capacity of the intercom power supply, the number and type of connected user devices, and the length and type of the interconnecting cables. The capacity of the intercom power supply must meet or exceed the needs of the connected user devices, including the Model 45A.
It’s important to remember that if an external source of 24 volts DC is connected it will always be used as the Model 45A’s power source. Even if switch 1 is in its on (up) position, power will be drawn from the connected intercom circuit only if the external source of 24 volts DC is not present.
The independent auto null mode allows the auto null function to be initiated for each channel as desired. A single “tap” will start the auto null routine for channel 1; two “taps” will start the routine for channel 2. that uses source assignment panels. The “SAP” panels would be used to route multiple intercom channels to various sets of user devices as desired. In this case, the two channels associated with the Model 45A’s interface will often end up not routed to the same user device.
“loops” of single-channel beltpacks, such as units from Clear-Com, need to be connected. In this case the intercom circuit’s DC power will not be connected to the Model 45A, but only to the user devices. In this scenario, a DC voltage won’t be present on pin 2 or pin 3. Another example of this might be where adapter boxes with DC blocking are used to interconnect intercom circuits with the Model 45A.
Operation Upon power-up the Model 45A will always go through a short initialization sequence before normal operation will begin. The LEDs will light sequentially and, upon completion, the applicable input power LED will light. The null settings for the two hybrid circuits are recalled and used, having been previously stored in nonvolatile memory. Significant user intervention is typically not required during normal Model 45A operation.
indication that an active intercom circuit is connected. In this case the 200 ohm termination is expected to be provided elsewhere, typically as part of the external power supply, and the Model 45A’s termination is “lifted.” When the Model 45A is Serving as the 2-Wire Intercom Power Source When configuration DIP switch 2 is set so that the Model 45A provides 2-wire (PL) power its interface supplies 30 volts DC on pin 2 of the 2-wire (PL) intercom connectors.
lit, indicating that power in excess of 20 volts is detected on pin 2. The pin 3 LED will also light if the same condition is present on pin 3. Level Meters The Model 45A contains four 5-segment LED level meters. These meters are provided as a support aid during installation, configuration, operation, and troubleshooting. The meters represent the strength of the signals coming in from, and going out to, the 4-wire connections.
on the same circuit, will cause a “doubletermination” condition. This leads to a nominal 100 ohm line impedance which will result in a level drop of at least 6 dB. Removing the unwanted termination is really the only valid means of correcting the problem. Auto Null The Model 45A contains circuitry to automatically null the two 2-wire-to-4-wire interfaces.
to mute any active microphones. While the automatic “mic kill” signal will apply to many user devices it may not apply to all. Muting microphones is significant as obtaining a “deep” null requires that no extraneous signals be present on the intercom circuit. Auto Terminate Disable As previously discussed in this user guide, the auto terminate function can come into play when the 2-wire party-line interface is configured to not supply power.
the nulling process take place. But unless there’s a really good reason, configuration DIP switch 5 should always remain in its off (down) position. Technical Notes Software Version Display A special Model 45A power-up sequence allows the unit’s software version number to be displayed. This is useful when working with factory personnel on application support and troubleshooting situations. The five “from” 4-wire LEDs are used to display the major release number with a range of 1 through 5.
operating software (“firmware”). Re-programming this memory requires using a specialized programming unit. While not outrageous in price, it still costs in the range of US$500. The programmer uses a ribbon cable and socket to interface with a 6-pin “header” on the Model 45A’s printed circuit board. And, as you would guess, once connected reprogramming takes only a matter of seconds. But unfortunately the programmer is not something that would be found in a typical “field shop” or repair facility.
Specifications General Audio: 4-Wire Outputs: 2 Frequency Response: ±2.5 dB 100 Hz to 8 kHz Type: transformer-coupled, capacitor isolated Distortion (THD+N): <0.
Appendix A Interfacing RTS® Matrix Intercom Systems with the Model 45A Interface ADAM™ Matrix Intercom System Analog Ports to Model 45A Interface RVON-I/O I/O Connections to Model 45A Interface Issue 3, August 2015 Page 28 Model 45A User Guide Studio Technologies, Inc.
Appendix B Interfacing Riedel® Artist™ Matrix Intercom System Analog Ports with the Model 45A Interface Model 45A User Guide Studio Technologies, Inc.
Appendix C Interfacing Clear-Com® Matrix Intercom System Analog Ports with the Model 45A Interface Issue 3, August 2015 Page 30 Model 45A User Guide Studio Technologies, Inc.
Appendix D Model 45A Interface Front-Panel Configuration DIP Switch Settings 2-wire (PL) input power switch settings Auto terminate switch settings 2-wire (PL) power source switch settings 4-wire mute during auto null switch settings Auto null button switch settings Model 45A User Guide Studio Technologies, Inc.
