Before doing anything too extreme, try going through all the line in/out jacks etc, plugging into and removing plug maybe 6 times in each. just start at one side, and move through all of them....
if there is any corrosion on teh jacks which might mess up the "default through" connection in them, that should dislodge it.
if that makes a difference but not enough of one, do it again.
might work. bad contacts on that sort reduce volume, make the sound tinny and often distorted, etc.
if it was B stock, it might have some other problem, but in any case it is newer. I don't have a clue if they are still using the better jacks we specified for Ampeg..... The korean units may likely use not so good asian sourced jacks, which are more prone to corrosion problems. We used UK sourced jacks and eliminated those problems 99%.
Could be something else though...... remote diagnosis is pretty much guessing
