I have a first revision ADI-2 DAC that is connected to my PC via TOSLINK. I use it with headphones connected to the Phones output. The source is set to Optical for all outputs.

After a bit of silence from my PC, the DAC shows me that it switches from "SP o." to "INT" as its input. This is even with no other input but the TOSLINK connected. Then occasionally both the level meter and spectrum (for Phones, the output that I am using) that a short, potentially very loud (I have seen close to 0 dBFS) pop is played back, primarily (but not exclusively) in the left channel. However, I don't actually hear anything on my headphones, when these pops should be quite audible.

To me it looks like there are multiple things going wrong:

• The input seemingly "switches" to INT, even though I specifically tell the DAC that I only want Optical as input. However, the input does not actually switch to INT: When I connect another device via USB and play back audio, I hear nothing, because the actual input is still SP o. This is bad because the display of the DAC tells me I am listening to USB when I am actually listening to optical.

• For some reason, with no input feeding any audio signal to the DAC, audio seems to be detected.

• The incorrectly detected audio is then not actually played back. Three wrongs make a right? It appears the signal might just be a glitch in the meter and spectrum.

This is happening on USB 81/DSP 59, but I also observed it on 80/55.

Edit: When I set the input to USB, no pops are detected.