I have the following inputs on an audio device:

  • DAC audio signal
  • Secondary audio input signal

The device has one analog audio output. I want the output to source from the DAC when powered, and to source from the analog input when powered off. Originally I used a mux IC, but the power off condition does not work (DUH). How should I switch between these two audio signals based on the device's power state?

  • \$\begingroup\$ a relay might work \$\endgroup\$
    – jsotola
    Apr 17, 2020 at 1:38
  • \$\begingroup\$ Thanks jsotola, this is true, but a relay does not satisfy the form factor requirements. \$\endgroup\$
    – bcoo
    Apr 17, 2020 at 1:39
  • \$\begingroup\$ You can get very small reed relays the size of 14 or 16 pin DIP ICs. \$\endgroup\$ Apr 17, 2020 at 2:36

1 Answer 1


Any kind of an analog switch will need a bias voltage to operate. If you could bootstrap one from your external audio signal that might be just enough to get the job done. Then use the main power state to select the DAC.

  • \$\begingroup\$ How could this be done? any further insight? \$\endgroup\$
    – bcoo
    Apr 17, 2020 at 4:02

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