A switchless pre-amplifier input circuit includes an audio input connector that receives a first audio device operable at a first impedance and a second audio device operable at a second impedance less than the first impedance. A preamplifier circuit outputs a preamplified audio signal in response to amplifying a first audio signal generated by the first audio device or a second audio signal generated by the second audio device. The switchless pre-amplifier input circuit further includes a impedance selector circuit that adjusts an impedance at the output to reach the second impedance in response to connecting the second audio device to the audio input connector and to adjust the impedance at the output to reach the first impedance in response to connecting the first audio device to the audio input.