Studio Technologies Model 46A Dual 2-Wire to 4-Wire Interface

Dual 2-Wire Analog Audio to 4-Wire Analog Audio Interface

The Model 46 is designed to interface 2-wire full-duplex party-line intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Other specialized audio system interfacing applications can also be supported. The Model 46 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, allowing direct operation of devices such as user belt packs. 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 46 include television sports and special event broadcasting, theme park and theater installations, corporate events, and industrial testing environments. Standard audio connectors are used for all input and output signals. The Model 46 mounts in one space of a standard 19-inch rack enclosure and requires 100-240 volts, 50/60 Hz for operation.

2-Wire Interfaces
The Model 46's 2-wire interfaces are optimized for direct connection with dual-channel party-line (PL) intercom circuits. In addition, single-channel party-line intercom circuits can also be connected. Many broadcast applications use the dual-channel TW-series from Telex/RTS, including their popular BP325 belt pack. Other industry-standard single- and dual-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 46'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. For example, for applications that use equipment from RTS the -10 dBu setting is appropriate. For other equipment, such as that from Clear-Com, the -14 setting is correct.

The Model 46'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 PS31 or Clear-Com PS-232. This DC power, normally 30-32 volts, provides energy for connected devices such as user stations or belt packs. In this type of application the Model 46 is configured to operate in its external 2-wire power source mode. In this mode the Model 46'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 46'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 46's 2-wire interfaces is their ability to supply DC power and 200 ohm AC termination to the connected intercom circuits. Referred to as the Model 46's internal 2-wire power source mode, the 30 volt output can power devices such as user stations and belt packs. In many applications this will eliminate the need for external intercom power supplies. Besides reducing total system cost, this feature can also lower system weight, reduce required mounting space, and decrease the mains energy requirement.

With each 2-wire interface's ability to supply up to 300 milliamperes of current, a typical broadcast application that uses two sets of three BP-325 belt packs can easily be supported. Each interface's 30 volt DC intercom power source ensures that systems requiring 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 the output of the DC power supplies are monitored for over-current and short-circuit conditions. This allows protection shut-down of the output DC, 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
• Integrated intercom power sources
• Standard audio connectors
• Transformer-coupled 4-wire inputs and outputs
• "Universal input" mains powered