Studio Technologies Model 47A Dual 2-Wire to 4-Wire Interface

Dual 2-Wire Analog Audio to 4-Wire Analog Audio Interface with Dual-Pin Power

The Model 47A is designed to interface 2-wire full-duplex party-line (PL) intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Other specialized audio system interfacing applications can also be supported. The Model 47A provides two independent full-featured 2-channel interfaces. Each interface contains two hybrid circuits which include automatic nulling capability. The analog circuitry, under software control, provides excellent audio quality and high return-loss. The interfaces are compatible with powered and unpowered 2-wire party-line circuits. They are capable of supplying DC power to devices such as user beltpacks and user stations. Independent power sources are provided for both channels (pins 2 and 3) of each interface, allowing direct support for broadcast source assignment panel (SAP) applications. Configuration settings allow the 2-wire and 4-wire interface circuitry to be compatible with a range of nominal signal levels. Audio level meters provide user confirmation of system performance during setup and operation. Applications for the Model 47A include mobile and fixed television facilities, theme park and theater installations, and industrial testing environments. Standard audio connectors are used for all input and output signals. The Model 47A mounts in one space (1U) of a standard 19-inch rack enclosure and requires 100-240 volts, 50/60 Hz for operation.

2-Wire Interfaces
The Model 47A's 2-wire interfaces are optimized for direct connection with 2-channel party-line intercom circuits. In addition, single-channel party-line intercom circuits can also be connected. Many broadcast applications use the 2-channel TW-Series from RTS, including their popular BP325 beltpack. Other industry-standard single- and 2-channel PL intercom systems, including those from Clear-Com, are also directly compatible. To provide optimal signal matching and interface performance the nominal level of the Model 47A's 2-wire interfaces can be selected. Using DIP switches, accessible on the front panel, the nominal levels can be selected to be either -10 or -14 dBu, settings that should allow compatibility with virtually all party-line systems.

The Model 47A's 2-wire interfaces can correctly function with powered ("wet") or unpowered ("dry") intercom circuits. Powered circuits have a DC voltage present, typically provided by power supplies such as the RTS PS20. This DC power, normally 30-32 volts, provides energy for connected devices such as user stations or beltpacks. In this type of application the Model 47A is configured to operate in its external 2-wire power source mode. In this mode the Model 47A's circuitry maintains the required high-impedance load and, as in all cases, draws no power from the party-line circuit. An auto-terminate function ensures that should a "wet" circuit not be connected, the Model 47A's interface circuitry will remain stable. This unique feature makes certain that objectionable audio signals, including oscillations and "squeals," will infrequently be sent to the connected 4-wire device.

A significant capability of the Model 47A's 2-wire interfaces is their ability to supply DC power and 200 ohm AC termination to both channels (pins 2 and 3) of the connected intercom circuits. Referred to as the Model 47A's internal 2-wire power source mode, the 30 volt outputs can power devices such as user stations and beltpacks. With independent power sources provided for both pins 2 and 3 of each interface, applications that include flexible party-line intercom channel routing will be directly supported. As such, in applications that include both source assignment panel (SAP) and Model 47A units the need for external intercom power supplies can be eliminated. Besides reducing total system cost, this capability may also lower system weight, reduce required mounting space, and decrease the mains energy requirements.

With the Model 47A's 2-wire interfaces able to supply up to 315 milliamperes (mA) of current on each channel, a typical broadcast application that uses four sets of three BP325 beltpacks can easily be supported. And the sophisticated 30 volt DC intercom power sources ensure that applications that require long intercom cable runs will function correctly. The circuitry's output regulation is such that little change in the output voltage will occur over its entire rated output current. Also, the unique design of the power supply circuitry virtually eliminates the noise and "hiss" associated with typical intercom power supply performance. Under software control each of the four DC power sources is monitored for over-current and short-circuit conditions. This allows protective shut-down of individual DC outputs, as well as providing an alert by way of a visual indicator.

Features:

• Two 2-channel party-line intercom interfaces
• Four analog hybrids with auto null capability
• Input and output level metering
• Excellent audio quality
• 2-channel intercom power sources
• Direct support for broadcast SAP panel applications
• Standard audio connectors
• Universal input mains powered