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

Product Code: ST-M46A

Key Features
The Model 46A is designed to interface 2-wire full-duplex party-line (PL) intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Other specialised audio system interfacing applications can also be supported. The Model 46A 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 beltpacks. Configuration settings allow the 2-wire and 4-wire interface circuitry to be compatible with a range of nominal signal levels. Audio level metres provide user confirmation of system performance during setup and operation. Applications for the Model 46A include television sports and special event broadcasting,
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Studio Technologies Model 46A Dual 2-Wire to 4-Wire Interface

2-Wire Interfaces

The Model 46A's 2-wire interfaces are optimised 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 46A'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 46A'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 V, provides energy for connected devices such as user stations or beltpacks. In this type of application the Model 46A is configured to operate in its external 2-wire power source mode. In this mode the Model 46A'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 46A'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 46A'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 46A's internal 2-wire power source mode, the 30 V output can power devices such as user stations and beltpacks. 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 315 milliamperes (mA) of current, a typical broadcast application that uses two sets of three BP325 beltpacks can easily be supported. Each interface's 30 V 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.

Analog Hybrids with Auto Nulling

A key reason that the Model 46A's interfaces achieve excellent audio performance is the design of the 2-wire-to-4-wire hybrid circuits. They provide low noise and distortion, good frequency response, and high return-loss ("nulling"), even when presented with a wide range of 2-wire conditions. Unlike telephone-line ("POTS") oriented DSP-based hybrid circuits, the Model 46A'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 circuits.

A hybrid's ability to isolate the transmit signal from the receive signal in the 2-wire-to-4-wire interface is critical. The quality of this isolation, technically known as return-loss or trans-hybrid loss, is measured in dB. A high value is important, especially in applications where multiple 2-wire-to-4-wire interfaces are used together. Remote sports broadcast applications are especially sensitive to this requirement. The Model 46A's sophisticated auto nulling function uses analog circuitry under microprocessor control to achieve significant trans-hybrid loss. This return-loss "null" is achieved by making a series of adjustments to account for the resistive, inductive, and capacitive conditions that are present on the connected 2-wire party-line circuit. The party-line's conditions are the sum of the impact made by the type and quantity of cable, the connected user-devices, and the intercom power source.

Warranty

We offer a 3 year warranty on this product from its date of purchase. For more information regarding our support, repair and warranty, please download our Warranty Guide here.

Trade Terms
The above item is non-returnable, unless defective. Please ensure part numbers and descriptions are as required before placing this order. If any confirmation or information is required please contact AV Sales on 1800 00 77 80.
General Audio:
Frequency Response: ±2 dB 100 Hz to 8 kHz
Distortion (THD N): less than 0.5%, measured at 1 kHz, 4-wire input to 2-wire interface pin 2
Signal-to-Noise Ratio: greater than 55 dB, measured at 1 kHz, 4-wire input to 2-wire interface pin 2
Connectors:
Inputs from 4-Wire: 3-pin female XLR
Outputs to 4-Wire: 3-pin male XLR
2-Wire Party-Line Intercom: 3-pin male XLR
Remote Control: 10-pin header, requires optional 10-pin ribbon connector assembly
AC Mains: 3-blade, IEC 320 C14 (mates with IEC 320 C13)
2-Wire Party-Line Intercom Interfaces: 2
Type: 2-channel party-line (PL), unbalanced (pin 1 common; pin 2 channel 1 audio or DC with channel 1 audio; pin 3 channel 2 audio)
Compatibility: single- and 2-channel intercom systems such as from RTS® and Clear-Com®
Impedance, External Power Mode: >10 k ohms
Impedance, Internal Power Mode: 200 ohms
Nominal Level: –10 or –14 dBu, selectable
"Mic Kill" Signal: square wave, 24 kHz, ±1%
Internal Power Source: 30 Vdc nominal, 315 mA maximum
Hybrids: 4, 2 per interface
Topology: 3-section analog circuitry compensates for resistive, inductive, and capacitive 2-wire party-line loads
Nulling Method: automatic upon user initiation, processor implements digital control of analog circuitry; null settings stored in non-volatile memory
Nulling Line Impedance Range: 120-350 ohms
Nulling Cable Length Range: 0-3500 feet, typical
Trans-Hybrid Loss: greater than 40 dB, typical at 800 Hz

4-Wire Inputs: 4, 2 per interface
Type: transformer-coupled, capacitor isolated
Impedance: 13 k ohms
Nominal Level: 0, 4, 6, or 8 dBu, selectable in tandem with nominal output level
Maximum Level: 22 dBu
4-Wire Outputs: 4, 2 per interface
Type: transformer-coupled, capacitor isolated
Impedance: 50 ohms nominal
Nominal Level: 0, 4, 6, or 8 dBu, selectable in tandem with nominal input level
Maximum Level: 20 dBu into 2 k ohms
Meters: 8
Function: displays level of 4-wire inputs and outputs
Type: 5-segment LED, modified VU ballistics
Remote Control Inputs: 3
Type: optically coupled
Input: 3-32 Vdc; 2 mA minimum for operation, 20 mA maximum
Functions: auto null interface 1, auto null interface 2, and "mic kill"
AC Mains Requirements: 100-240 V (–15/ 10%), 50/60 Hz, 34 watts maximum
Dimensions (Overall):
19.0 inches wide (48.3 cm)
1.72 inches high (4.4 cm)
8.4 inches deep (21.3 cm)
Mounting: one space (1U) in a standard 19-inch rack
Weight: 4.6 pounds (2.1 kg)

Specifications subject to change without notice.

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