Thanks, jcx.   This makes me fairly certain there is something wrong with the ground connection in the jack of my portable device.   Could you please clarfiy what you mean by "drive V"? I am not using active headphones...   When I do connect the jack with the line-in of an active...

Pardon the bump, would anyone be willing to take a stab at this please?

    Question: What happens when the S conductor in a typical TRS jack of a device is not properly grounded or does not make contact with the S conductor in a TRS plug of a pair of headphones?   My guess: What one would "hear" is the equivalent of the side channel in a mid-side mix...