Abstract: Improvements to U.S. Pat. No. 5,428,642 including use of a single clock providing a first frequency to drive a power supply and a second frequency, twice the first frequency, to dual channel pulse width modulators and audio amplifiers. The power supply is improved to provide enough output voltage that the amplifier stays below 90% modulation and the first frequency driver eliminates the dead band, thereby improving efficiency. Current limiting, even against shorts in the load, is provided by inductor inputs to the clipper circuits, where the inductors are in the magnetic fields of the output chokes. The audio amplifiers are isolated by optical couplers for the audio signal and by an optical coupler and isolation transformers for the clock. One clock amplifier supplies both amplifier channels. The pulse width modulator uses the optically isolated clock and receives clipped audio directly. Two channels fit in the space of one old channel.

Abstract: Improvements to U.S. Pat. No. 5,428,642 including use of a single clock providing a first frequency to drive a power supply and a second frequency, twice the first frequency, to dual channel pulse width modulators and audio amplifiers. The power supply is improved to provide enough output voltage that the amplifier stays below 90% modulation and the first frequency driver eliminates the dead band, thereby improving efficiency. Current limiting, even against shorts in the load, is provided by inductor inputs to the clipper circuits, where the inductors are in the magnetic fields of the output chokes. The audio amplifiers are isolated by optical couplers for the audio signal and by an optical coupler and isolation transformers for the clock. One clock amplifier supplies both amplifier channels. The pulse width modulator uses the optically isolated clock and receives clipped audio directly. Two channels fit in the space of one old channel.

Abstract: The instant invention provides a system and method of broadcasting audio and visual information to a plurality of audio reproduction devices and visual display devices utilizing a plurality of control computers linked thereto by a communications network. The invention employs a plurality of pre-recorded digital audio files and corresponding visual representation thereof to allow a user to construct message sequences for broadcast with a minimum of system input. Furthermore, a user may specify a plurality of broadcast zones to broadcast audio and visual messages.