a switching operation is performed in response to an externally applied dc control signal from an external load . an input connector receives an input audio signal from an external audio source , and an output connector that provides an audio output signal . a dc isolator couples the input audio signal from the input connector as the audio output signal on the output connector while isolating the externally applied dc control signal from the input connector . a switch is responsive to the externally applied dc control signal applied to the output connector so as to perform the switch operation .