http://ubuntuone.com/2XFn7ygpPzE5t5v6gnH9c1
Ubuntu Sound Control
accessed from System Settings / Sound
notes
1. make sure the proper device is selected. notice I have a CODEC as well as built in sound
2. make sure amp is connected to device you want to use lime green jack is stereo L-R
3. watch the output volume . mine like to reset itself to the on-board port and sets the audio codec to zero . ( why doesn't software do what it's told ? ) .
4. press the sound test to check things out
5. check your playback software: som always play thru the default device; others allow you to select an output device .