Intercom Interface
Of special note is the Model 233’s sophisti- cated intercom interface. It’s designed
to work correctly with industry-standard single- and dual-channel party-line inter- com systems, including those from RTS and Clear-Com. An intercom line connect- ed to the Model 233 can serve three func- tions: providing cue audio signals to the headphone output, allowing talkback audio to be sent to intercom users, and acting as a Model 233 power source. Audio sig- nals present on the single- or dual-channel intercom line can be flexibly routed to the stereo headphone output. Talkback audio, controlled by the two talkback pushbutton switches, can be sent to either or both of the intercom channels. Trim potentiom- eters, located on the bottom of the unit, al- low adjustment of the talkback-to-intercom sidetone (null) level.
Other announcer console products can exhibit talkback-to-intercom-related audio oscillations (“squeals”) that end up in the headphone output. A unique Model 233 feature ensures that this will never occur. This is accomplished by means of a special “auto-terminate” circuit that becomes active whenever an intercom line is not connected to the Model 233.
Audio Quality and Protection
The Model 233’s circuitry is carefully tailored to provide excellent audio perfor- mance. Professional-quality components are featured throughout. For reliability all audio routing is performed using solid-state devices under microcontroller direction. 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.
Power Sources
The Model 233 can derive its operating power from an intercom line or an external 24 volt DC source. For redundancy, both power sources can be connected simul- taneously. An internal switch-mode power supply ensures that all Model 233 features are available, including phantom power, when the unit is powered by either source.
Auxiliary Relay
Model 233 resources include a general- purpose relay, allowing specialized configu- rations to be created. Under software con- trol, the relay can be configured to follow the state of the main output, talkback 1,
or talkback 2 buttons. Taking advantage of the back-panel locations provided for additional XLR-type connectors, a techni- cian may easily create functions such as an “on-air” indicator or implement a loud- speaker muting during talkback function. Special configuration modes are even included to allow direct control of the relay using the talkback 1 or talkback 2 buttons without impacting any of the Model 233’s audio signals.
Tally Output
Another unique Model 233 feature is the tally output. It provides an indication, in the form of a current-limited DC signal, of the status of the main output. Whenever the main output is active the tally output is active. This 3.5 volt nominal, 12 milliam- peres maximum, signal is capable of di- rectly lighting an LED indicator or triggering an external control system. The tally output is provided specifically for specialized ap- plications such as television award show broadcasts where remote monitoring and control of the main output is required.
