Bose QC20 Noise-cancelling Headphone Signals

Bose QuietComfort QC20 Noise Canceling headphones (they’re actually earbuds) come in Apple and Android versions that (probably) differ only in the connector pinout. Given that the connector has four conductors, I was surprised to find only half a dozen different possibilities, with only two for purely audio connectors.

These QC20 earbuds came in the Android flavor, also known as the CTIA/AHJ “standard”:

Bose QC20 Earphones
Bose QC20 Earphones

The 3.5 mm plug connections:

  • Tip = left audio
  • Ring 1 = right audio
  • Ring 2 = ground
  • Sleeve = microphone and button signals

The blue Mode button on the side of the splitter box switches the noise cancelling between “some” and “silent”. The latter works surprisingly well; it can knock our vacuum cleaner down to a bearable level.

The three black buttons place resistive loads on the otherwise open-circuit microphone connection:

  1. Volume + = 220 Ω
  2. Answer/End = 56 Ω
  3. Volume – = 520 Ω

Now, if only I had a device that would do something with those signals …