Abstract: An end-of-line module provided at the end of the line of an audio circuit provides a load in response to a test signal. The load is detectable by an announcement control system so that a fault indication may be triggered in the event the announcement control system does not sense the end-of-line module as being connected to the audio circuit and detects an interruption in the audio circuit. In addition, the end-of-line module may include an over-temperature sensor or protection device to prevent the audio circuit from exceeding a predetermined limit, for example, a temperature level assigned to insure compliance with fire, safety and other standards or specifications. A fault or other indication may be reported to or sensed by the announcement control system and may be further processed in a manner appropriate for the application and/or facility having the announcement control system.

Abstract: The instant invention provides a digital audio processing system that includes a mainframe chassis, a central processor card, a plurality of analog input cards, and a plurality of analog output cards for accepting a plurality of audio inputs and producing a plurality of mixed audio outputs.

Abstract: A signal amplifier device providing output power independent of change in output characteristics or common mode interference including a signal input source to provide an input signal, a first power supply and second power supply having a transformer with a secondary coil and a reference power, first differential amplifier powered by the first power supply to receive the input signal and provide first and second complementary output signals, first and second output amplifiers driven by the reference power supply and each having an input to receive one of the first and second signals and amplify same to provide first and second output signals at the respective outputs so that upon imposition of a transient signal at the output of one of the first and second output amplifiers an isolation network prevent the transient signal from appearing as a differential signal on either output.