Studio Technologies Model 47 Interface Details
Studio Technologies Model 47 Interface 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. Studio Technologies Model 47 Interface 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 Studio Technologies Model 47 Interface 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. Studio Technologies Model 47 Interface mounts in one space (1U) of a standard 19-inch rack enclosure and requires 100-240 volts, 50/60 Hz for operation.
Studio Technologies Model 47 Interface'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 RTSÂ®, including their popular BP325 beltpack. Other industry-standard single- and dual-channel PL intercom systems, including those from Clear-ComÂ®, are also directly compatible. To provide optimal signal matching and interface performance the nominal level of Studio Technologies Model 47 Interface's 2-wire interfaces can be selected. Using DIP switches, accessible on the front panel, the nominal levels can be selected to be either â?"10 or â?"14 dBu, settings that should allow compatibility with virtually all party-line systemss.
Studio Technologies Model 47 Interface'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 Studio Technologies Model 47 Interface is configured to operate in its external 2-wire power source mode. In this mode Studio Technologies Model 47 Interface'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, Studio Technologies Model 47'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 Studio Technologies Model 47 Interface'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 Studio Technologies Model 47 Interface's internal 2-wire power source mode, the 30 volt output 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 Studio Technologies Model 47 Interface units the need for external intercom power supplies can be eliminated. 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 BP325 beltpacks can easily be supported. And the sophisticated 30 volt DC intercom power sources ensure 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 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 Studio Technologies Model 47 Interface'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, Studio Technologies Model 47 Interface'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. Studio Technologies Model 47 Interface'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.
Whenever a user presses one of Studio Technologies Model 47 Interface's "auto null" buttons digital circuitry adjusts the analog hybrids to rapidly achieve their maximum return-loss. The nulling process takes less than 10 seconds for each channel of an interface. However, it's important to note that while the nulling process is automatic, it only takes place upon user request. This can lead to more stable and consistent audio performance when a hybrid is exposed to the varying 2-wire conditions often found in broadcast applications. The parameters obtained during the nulling process are stored in non-volatile memory; mains power interruptions won't require the auto nulling function to again be performed.
A sine-wave audio tone is generated for use during the auto nulling process. The frequency is software-controlled to maximize the ability of the hybrid circuits to reach a "deep" null. In addition, at the beginning of each auto null sequence a short period of 24 kHz tone is sent to the associated 2-wire party-line interface. This serves as a microphone disable ("mic kill") signal for user devices such as the RTS BP325. By automatically disabling "open" microphones the auto nulling process can achieve better performance.
Associated with the 4-wire portion of the Model 47's interfaces are analog line-level inputs and outputs. These are intended to interconnect with a variety of 4-wire devices, including matrix intercom systems, audio-over-fiber transmission systems, and other specialized audio equipment. The input and output circuitry is transformer-coupled to minimize the chance of hum, noise, or ground "loop" issues. A key characteristic of Studio Technologies Model 47 Interface's design is the ability to select the 4-wire input and output nominal levels. This helps to ensure compatibility with virtually all audio equipment. Front-panel-accessible DIP switches allow the nominal levels to be configured from among four choices: 0, +4, +6, or +8 dBu. The 0 dBu setting was specifically provided for compatibility with Clear-Com matrix intercom systems. The +4 dBu setting allows "standard" audio signals to be directly connected. Digital matrix intercom systems from RiedelÂ® can be effectively connected using the +6 dBu setting. And the +8 dBu setting allows proper level matching with the popular ADAMÂ® series of matrix intercom systems from RTS. This setting also applies to the related RVON-I/O VoIP product.
Studio Technologies Model 47 Interface contains eight 5-segment LED level meters. Four of the meters are provided for each interface, with two displaying the level of the signal being received from the 4-wire source and two displaying the level being sent to the 4-wire output. During installation and setup the meters are invaluable in helping to confirm that the nominal level DIP switch settings have been properly made. During normal operation the meters offer rapid confirmation of audio signal flow in and out of the unit. Additional LED status indicators are also provided, offering a clear view of the 2-wire DC power and auto null functions.
Pro Audio Quality
Studio Technologies Model 47 Interface's audio circuitry was designed in the spirit of professional audio equipment, rather than that found in typical party-line intercom gear. High-performance components are used throughout, providing low-distortion, low-noise, and high headroom. Using passive and active filters, the frequency response is limited to approximately 100 Hz to 8 kHz. This range was selected to provide excellent performance for human speech, while maximizing the ability of the hybrids to create substantial "nulls." When Studio Technologies Model 47 Interface's internal DC power sources are selected to provide 2-wire party-line intercom power, enhanced audio performance can also be expected. The quality of the DC supply circuits is excellent, with very little noise, hum, or "hiss" being added to the 2-wire connections.
Attention to detail is a hallmark of Studio Technologies Model 47 Interface's design. For example, during the brief auto nulling process an interface channel's 4-wire input and output signal is muted, preventing unwanted audio from reaching the connected equipment. Associated with the 2-wire interfaces is circuitry that, under software control, applies 200 ohm terminating impedances to the 2-wire party-line circuits. This, along with other circuitry that monitors DC voltages present on the 2-wire circuits, ensures that audio instability associated with unterminated circuits will rarely occur. As previously mentioned Studio Technologies Model 47 Interface's 2-wire DC power sources offer a unique level of performance. Their ability to deliver power while maintaining audio quality is simply unmatched.
While Studio Technologies Model 47 Interface is designed to directly integrate into typical applications, it's ready to support the "one-in-a-million" situations too. To accomplish this DIP switches, accessible on the back panel, allow some of the automatic features to be disabled. For example, one switch allows the auto-terminate feature to be disabled. While this feature can help maintain audio quality, advanced users might need to disable it. This would allow full control over Studio Technologies Model 47 Interface's four hybrid circuits, enabling them to be used completely independently. A second DIP switch changes the way in which the front-panel auto null pushbutton switches operate. Normally pressing one of the buttons begins the process of auto nulling both channels associated with an interface. The alternate switch mode allows each auto null sequence to be activated independently. One tap of the auto null button will begin the auto null process for interface one. Two taps of the button will begin the auto null process for channel two. For installer-selected applications, three opto-coupled inputs allow selected Studio Technologies Model 47 Interface features to be remotely controlled. These features include remote auto nulling for each interface and remote "mic kill" activation.
Studio Technologies Model 47 Interface uses standard 3-pin XLR-type connectors to allow convenient interconnection in most broadcast and general audio environments. For flexibility, access to the 2-wire party-line intercom interfaces can be made using the connectors provided on both the front and back panels. In permanent installations the back-panel connectors will typically be utilized. In other settings, such as field television production, front-panel access allows intercom beltpacks to be rapidly connected, without requiring access to the inside of a rack enclosure or necessitating the use of a secondary input/output (I/O) panel.
Studio Technologies Model 47 Interface is housed in a rugged steel enclosure that is designed to be "road tough." It mounts in one space of a standard 19-inch rack enclosure. The mains input source can range from 100 to 240 volts, 50/60 Hz allowing direct operation virtually anywhere in the world. A switch-mode power supply, contained within Studio Technologies Model 47 Interface's enclosure, provides conversion of the mains input power into the DC voltage required by the intercom power supply circuits. Also contained within the unit is a DC-to-DC converter that creates the voltages required by the analog and digital circuitry. These efficient power supplies help to ensure cool, reliable operation in a variety of settings.
While the "bits and pieces" that make up Studio Technologies Model 47 Interface have been described in conventional terms, the real strength of the unit rests in how it integrates and performs in the "real world." Before beginning Studio Technologies Model 47 Interface's design process, conversations with industry experts quickly made it apparent that installing and configuring existing 2-wire-to-4-wire interface units was invariably a time-consuming, aggravating process that required the talent of an expert to achieve reasonable results. And even under those constraints the resulting audio performance was often mediocre. Any new design had to look at the application in a different way. This led to the over-riding Studio Technologies Model 47 Interface design goal: create a "new breed of cat," fundamentally changing how broadcast 2-wire-to-4-wire interface equipment fit into actual applications.
An important first step was to eliminate the requirement that a senior technician, along with a screwdriver, be present during every installation. (It was universally acknowledged that their time can be better spent elsewhere!) The need to adjust trim potentiometers, fabricate special cabling and connector straps, use nulling earpieces, etc. had to be eliminated. For example, in virtually all instances, input and output levels fall within just a few dB of their nominal values and, as such, could be supported with a limited number of configurable choices. In addition, it was acknowledged that in this application analog audio circuitry was capable of providing excellent audio performance, but that the required manual nulling process was operationally taxing. By adding digital control to the analog circuitry, automatic nulling could be performedâ?"the best of both worlds!
The next step was to identify resources that would improve the installation process and make operation more reliable. This led to the inclusion of multiple LED level meters, allowing continuous monitoring of the input and output signals. It also turned out that in many applications only a small number of user devices, such as beltpacks, are typically connected to 2-wire party-line circuits. But power on both pins 2 and 3 of each interface was necessary for compatibility with SAP panel applications. By adding DC power sources to Studio Technologies Model 47 Interface's 2-wire interfaces, the need for external intercom power supplies could often be eliminated.
The final step was to create a physical package that would provide significant resources in a form that allowed simple and reliable integration with other equipment. This was accomplished by including two 2-channel interfaces in a 1U enclosure. Using standard 3-pin XLR-type audio connectors would enable rapid installation and troubleshooting. And by making Studio Technologies Model 47 Interface "universally" powered, installation in any locale could be directly supported.
Studio Technologies Model 47 Interface Interface Features
- Two 2-channel party-line intercom interfaces
- Four analog hybrids with auto null capability
- Input and output level metering
- Excellent audio quality
- Dual-Channel intercom power sources
- Direct support for broadcast SAP panel applications
- Standard audio connectors
- "Universal input" mains powered
Studio Technologies Model 47 Interface Specifications
- Manufacturer: Studio Technologies
- Product: Model 47 Interface
- Frequency Response: Â±2 dB, 100 Hz to 8 kHz
- Distortion (THD+N): <0.5%, measured at 1 kHz, 4-wire input to 2-wire interface pin 2
- Signal to Noise Ratio: >55 dB, measured at 1 kHz, 4-wire input to 2-wire interface pin 2
2-Wire Party-Line Intercom Interface
- Interfaces: 2
- Type: 2-channel party-line, unbalanced (pin 1 common; pin 2 DC with channel 1 audio; pin 3 channel 2 audio or DC with Channel 2 audio)
- Compatibility: Single- and dual-channel intercom systems such as from RTSÂ® and Clear-ComÂ®
- Impedance External Power Mode: >10 k ohms
- Impedance Internal Power Mode: 200 ohms
- Nominal Level: â?"10 or -14 dBu (selectable)
- "Mic Kill" Signal: Square wave, 24 kHz, Â±1%
- 2-Wire Party-Line Power Sources: 4, 2 per interface
- Rating: 30 volts DC nominal, 300 mA max. software monitored & controlled
- Hybrids: 4 (2 per interface)
- Topology: 3-section analog circuitry for resistive, inductive, and capacitive 2-wire party-line loads
- Nulling Method: Automatic upon user initiation
- Nulling Line Impedance Range: 120 to 350 ohms
- Nulling Cable Length Range: 0 to 3500 feet, typical
- Trans-Hybrid Loss: >40 dB, typical at 800 Hz
- 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
- 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 output 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
- 4-Wire Line Inputs: 3-pin female XLR-type
- 4-Wire Line Outputs: 3-pin male XLR-type
- 2-Wire Party-Line Intercom: 3-pin male XLR-type
- Remote Control: 10-pin header, requires optional 10-pin ribbon connector assembly
- AC Mains: 3-blade, IEC 320 C14 (mates with IEC 320 C13)
Remote Control Inputs
- Type: Optically coupled
- Input: 3-32 V DC, 2 mA minimum for operation, 20 mA max.
- Functions: Auto null interface 1, auto null interface 2 & "mic kill"
AC Power Requirements
- Volts: 100-240 volts (â?"15/+10%), 50/60 Hz
- Max. Current: 1.2 A max. @ 100 volts, 0.7 A max. @ 240 volts
- Width: 19.0 inches wide (48.3 cm)
- Height: 1.72 inches high (4.4 cm)
- Depth: 10.3 inches deep (26.2 cm)
- Weight: 8.6 pounds (3.9 kg)
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