It seems quite a few people have trouble with their speakers/headphones after upgrading tu ubuntu 10.10, but my problem is slightly different.
I have a desktop pc with a Realtek ALC892.
I have no speakers connected to the computer, but occasionally plug headphones into the front jack. When I do this, the field "connector" in the sound settings dialog switches from "analog speakers" to "analog headphones", but then I hear no sound at all through the headphones. Only when I manually switch said field back to "analog speakers" can I hear something.
The funny thing: If I plug in the headphones and try to fiddle with the controls in alsamixer (which means trying out setting different levels for different devices) nothing happens. The only way to get sound on my headphones is to always manually switch the "connector" to "analog speakers" in the dialog box.
I did not have these troubles in Ubuntu 11.04.