SIGA amplifiers are high efficiency switch mode audio amplifiers available in 30 and 50 watt sizes. Amplifiers have two input channels supporting dual channel or single channel audio applications. Amplifier project application flexibility is enhanced by provision for input levels at 1Vrms or 25Vrms. This allows SIGA amplifiers to obtain their input from a line level signal or the output of another 25Vrms amplifier. This feature provides great application flexibility helping meet project requirements. Input channel selection is made through system software programming transmitted to the amplifier via a Signature data circuit. This reduces wiring interconnect requirements by reducing the number of control modules needed. Each amplifier has provision for connecting back up amplification. Amplifiers can be backed up one-to-one or multiple amplifiers can have one shared back up amplifier. In addition to back up amplifiers each SIGA amplifier has an on board 1kHz tone generator that can activate in the event of input failure or if no back up amplifier is availab