Cause of Channel Imbalance

Are your speakers properly connected in phase? Double check.
Is the area around the speakers reasonably symmetrical?
These are two potential reasons.

Will

I too had such problem but having in mind my two kids I spotted that ballance knob arn't in the middle:-)

Make sure your speakers have not moved - they should both be EXACTLY the same distance away from your listening chair. I like to attach a string to the center of the chair and move it back and forth between the 2 speakers' tweeters. Both directions should yield the same amount of tightness. Try it! ...John

Another possibility could be the interconnect cables themselves. It's happened to me. Turnes out to be an intermitant short in one of the cables. Try switching the L and R cables and see if the problem changes channels

To Seandtaylor99,

Thanks. I will try that and see what happens.

Neal

Is the channel imbalance the same at all volumes ? If it's worse at low volumes then it's likely a bad volume pot.

Did you try switching the pre->amp interconnects to see if it's in the pre or the amp ? IF you switch the pre->amp interconnects and speaker cables so you're using the L channel in the amp to driver the R speaker and vice-versa then that will isolate whether it's a preamp or amp issue.