Whether it's microphone switching, talkback outputs, or headphone cue feed, superior audio quality is maintained throughout. A microprocessor provides the Model 220's logic power, allowing exacting control of the unit's operation. With extensive flexibility built in, creating the desired operating configuration is a simple matter. While the operating features of the unit can be extensively configured, the user is presented with an easy-to-use set of controls and indicators. Power on the inside, simplicity during use—that's the hallmark of the Model 220.
A truly next-generation product, extensive research into the needs and desires of field production personnel was integral to the Model 220's creation. While primarily targeted for on-air television applications, specialized features are included to allow the Model 220 to be used in a variety of other audio applications. These include on-air radio broadcasting, stadium announcement, and voice-over/narration booths.
A high-performance microphone preamplifier circuit provides low-noise/low-distortion amplification over a 20 to 60 dB gain range. The gain is adjustable in 10 dB steps. The input is compatible with balanced dynamic and condenser microphones. The microphone power source is 48 V nominal and meets the worldwide P48 phantom power standard. An LED indicator serves as an aid for optimizing the setting of the preamplifier's gain. The output of the microphone preamplifier is used by the main output as well as being routed to the compressor circuit that supports the talkback functions.
The Model 220 provides a main output that is designed to serve as the on-air, stadium announcement, or other primary audio feed. Nominally –2 dBu, it is designed as a fully professional interface with high output capability, low distortion, and low noise. It features a high-performance output transformer expressly designed for professional audio applications.
The two talkback outputs are intended to provide production trucks, control rooms, or support personnel with talent-originated cue signals. These outputs are transformer-coupled with +4 dBu nominal signal levels. They contain resistors in series with their output connector, allowing the talkback outputs from multiple units to be directly "summed."
For non-on-air applications, a special Model 220 feature can be enabled, placing the unit in a "production" mode. This allows the main output to be used as a third talkback output. In this configuration the unit can be even more powerful when used in corporate or theatrical events, for example serving as a master console for a production director.
Dynamic Range Control
A studio-quality compressor circuit is provided to control the dynamic range of the signal coming from the microphone preamplifier. Far from a simple "clipper," the circuit utilizes a sophisticated laser-trimmed voltage-controlled-amplifier (VCA) integrated circuit for quiet, low-distortion level control. The signal from the compressor is always used by the talkback outputs. In addition, the audio source for the main output can be selected to be either the output of the microphone preamplifier or the output of the compressor. While possibly not appropriate for major on-air situations, having dynamic range control of the main output can offer increased performance for many applications. These could include stadium announcement positions, sports events using nonprofessional on-air talent, and situations where cable crosstalk is of concern.
User Controls and Status Indicators
Three pushbutton switches, four LED indicators, and two rotary controls provide the user with a clear, easy-to-use inter-face. One pushbutton switch controls the status of the main output. This is the audio output intended for on-air, announcement, or other primary uses. Two LEDs display the on/off status of the main output. Two additional pushbutton switches control the status of the two talkback outputs. These are the audio outputs used to communicate with producers, directors, "spotters," or other behind-the-scenes production personnel. A status LED is associated with each talkback button. Two rotary controls allow the user to adjust the level of the headphone output.
A large part of the Model 220's unique power is the ability to configure the operation of the main output and talkback functions. To meet the needs of the many specific broadcast and production applications, a variety of button operating modes is available. The main output button can be selected to operate from among four modes. In the "push-to-mute" mode the button performs a momentary mute of the main output. In this way a "cough" button function is created, something typically required for television sports broadcasting. In the "push-to-talk" mode the button provides a momentary active function for the main output. This mode would be appropriate for applications such as stadium announcement. An alternate action "latching" configuration allows the button to enable or disable the main output as desired. This is useful in radio broadcasting, announce-booth, or voice-over applications. The fourth mode provides a hybrid function, supporting both push-to-talk and tap-to-enable/tap-to-disable operation. This operation is similar to that found in many broadcast intercom system user stations.
The two buttons associated with the talkback functions can be configured to operate from either of two modes. One of the modes supports a "push-to-talk" function. This is typically used for on-air broadcast applications. The other mode provides a hybrid function, the operation of which is discussed in the previous paragraph. The hybrid mode is especially useful when the Model 220 is used in a production-support application.
In addition to the two modes provided for talkback 1, the button associated with talkback 2 supports three additional operating modes. One mode allows talkback 2 to be disabled. This is useful when only talkback 1 is to be utilized. The other two modes provide special momentary and hybrid functions. With these modes the operation of the main and talkback outputs are not impacted. This allows the talkback 2 button to control the state of the Model 220's auxiliary relay, making specialized implementations possible.
The main button mode configures how the main output, when it is in the "latched" on state, responds to talkback activity. One choice momentarily turns off the main output when talkback is active, returning the main output to the on state when the talkback function has ended. The other choice "unlatches" the main output in response to a talkback function.
A broadcast-standard "wet" (DC with audio) IFB circuit can be directly connected to the Model 220's IFB input. Originated by sources such as the RTS® 4000-series IFB system or IFB interface devices from Studio Technologies, the connected IFB circuit can provide DC power to operate the Model 220 as well as two channels of cue audio.
The Model 220 allows up to four audio sources to be selected for routing to the headphone output. The sources are IFB channel 1, IFB channel 2, line input 1, and line input 2. Each source can be individually assigned to the left channel, right channel, or both left and right. This allows a wide variety of stereo and mono headphone mixes to be created.
The two audio signals associated with the IFB input can be assigned to the headphone output. Originating in production trailers, control rooms, or remote locations, these unbalanced sources normally provide DC power and program-with-interrupt audio on one channel and program-only audio on the other.
For application flexibility, two line-level audio sources can also be connected to the Model 220. Possible signal sources include off-air receivers, wireless IFB systems, and audio consoles. The connected signals can be from two independent sources, or could be a stereo audio feed such as would be associated with a broadcast music event. Two trim potentiometers, located on the bottom of the unit, allow signals with wide nominal audio levels to be cleanly interfaced.
Two rotary controls are provided for user adjustment of the headphone output levels. For application flexibility, the actual function of the two "pots" is configurable. For traditional on-air sports applications they can be selected to the dual level control mode, which provides independent control of the left and right channel volume. For use with stereo cue signals, or to support user preference, the level/balance mode can be selected. In this mode one control adjusts the overall level of both the left and right channels, while the other allows adjustment of the left/right level balance. To help minimize the chance of broadcast cues being missed, both level control modes can be configured so that a minimum headphone output level is maintained. Alternately, the headphone output can be set to fully mute when the controls are at their minimum position.
The headphone output was designed to meet the needs of contemporary headphones and headsets. Specifically, the output circuits act as voltage, rather than power, drivers. In this configuration they can provide high output levels with very low distortion and noise, along with minimal current consumption. The output circuits are configured to safely drive stereo or mono loads. This ensures that all types of headphones, headsets, and earpieces can be directly connected.
Audio Quality and Protection
The Model 220's circuitry is carefully tailored to provide excellent audio performance. Professional-quality components are featured throughout. For reliability all audio routing is performed using solid-state devices. In all critical audio paths, "clickless" electronic switches provide noise-free control. All audio inputs and outputs make extensive use of protection components. This limits the chance of damage from ESD and other undesirable, yet real-world, hazards.
The Model 220 can derive its operating power from either the IFB input or an external nominal 24 Vdc source. For redundancy, both power sources can be connected simultaneously. An internal switch-mode power supply ensures that all Model 220 features, including phantom power, are available when the unit is powered by either source.
The Model 220 is compatible with IFB circuits provided by most standard broadcast systems. However, maximum performance can often be obtained by using the IFB interface devices available from Studio Technologies. The provide high-quality audio along with an excellent source of DC power. They're directly compatible with most matrix intercom systems, as well as standard line-level audio signals.
The Model 220's circuitry includes a general-purpose relay, allowing specialized configurations to be created. Under software control, the relay can be configured to follow the state of the mic, talkback 1, or talkback 2 buttons. Taking advantage of the locations provided for additional XLR connectors, a technician may easily implement a variety of functions such as mic active indication, audio muting during talkback, or audio insertion control. Several modes were specifically included to allow direct control of the relay using the talkback 2 button, without impacting any of the audio signals. The auxiliary relay is also used by the optional direct microphone output card.
Model 220 configurations are made using a number of DIP switches and two trim potentiometers. One 8-position switch assembly is used to set the gain of the microphone preamplifier and the on/off status of phantom power. Another 8-position switch assembly configures which of the cue audio sources are routed to the headphone output. Two additional 8-position switch assemblies communicate the desired operating modes to the microprocessor. Two rotary trim pots are used to adjust the input sensitivity of the line inputs. All switches and trim pots are accessible via the bottom of the Model 220's enclosure; the unit does not have to be disassembled. Changes made to any of the configuration parameters become active immediately. To prevent access to the configuration controls a security plate, included with each unit, is attached to the bottom of the enclosure.
The Model 220 uses standard connectors throughout. The microphone, IFB, and line inputs use 3-pin female XLR connectors. The main and talkback outputs use 3-pin male XLRs. The headphone output utilizes a ¼-inch 3-conductor jack. The external source of 24 Vdc power is connected by way of a 2.1 x 5.5 mm "locking" coaxial power jack.
Additional Connector Locations
In the world of broadcast and production audio it's fair to say that applications vary widely. To this end, up to three additional XLR connectors can be easily mounted into the Model 220's back panel. Multiple 3-position "headers" located on the Model 220's circuit board provide technician-access to literally every input and output connection. Using a factory-available interface cable kit, these allow a Model 220 to be optimized to meet the exact needs of specific applications. For example, some applications may prefer to use a multi-pin XLR connector to interface with a headset. This could be easily accomplished by adding the appropriate 5-, 6-, or 7-pin XLR connector and making a few simple connections. Other applications may benefit from having "mult" or "loop-through" connections, something easily incorporated into a Model 220.
Multi-Pin Headset Connectors
As previously mentioned, some broadcast applications use headsets that interface using a multi-pin connector. In most cases these connectors are 5-, 6-, or 7-pin male XLRs wired to an industry-standard pinout scheme. Studio Technologies offers headset connector assemblies that allow fast and painless installation into a spare connector location in the Model 220's back panel.
The Model 220's standard resources are more than sufficient to directly support a large number of applications. But in the "real world" of audio and intercommunications special needs always seem to arise. To that end, Studio Technologies offers a number of option cards. In addition to passive or active components, each card contains an integral connector, allowing simple installation into a spare connector location on the Model 220's back panel. For interest, the resources provided by some of these option cards are worth describing.
- The direct microphone output card provides access to the dynamic or condenser microphone that is connected to the Model 220's mic input. Passive components, along with the auxiliary relay contact, create a "click-free" microphone-level audio signal.
- The remote switch input card uses a 4-pin XLR connector to provide access to the Model 220's remote switch inputs.
- The tally/remote switch input card provides a current-limited DC voltage that serves as a main output status signal. It also provides a remote switch input connection.
Other general purpose option cards provide 3-pin XLR, 4-pin XLR, and 8-pin EtherCon® connectors. With the range of option cards available it's hard to imagine an application that can't be served. But you're welcome to try to "stump the chumps" in the Studio Technologies technical support department! But first please check the complete list of the available option cards.