Abstract: Combination line/microphone input circuitry is provided that adapts to receive either an audio line input or a microphone input via a single dual-purpose compound plug or input. More particularly, a combination line/microphone input circuit is provided to accept two different types of audio signals, being audio line signals and microphone signals, via a single dual-purpose plug or single input, such that the audio input circuitry is controlled or switched to accept either the audio line input or the audio microphone input signals, appropriately attenuate, filter and/or such input signals as necessary, then provide the resulting signal to other audio circuitry. Embodiments of the invention include additional circuitry that helps protect external line signal producing electronics from receiving incorrectly activated phantom microphone voltage.