One Channel of Magnepan Mini Maggie sounds lower than the other

Hello tiofelon,

     It could be a lot of things, from a bad source, amp or preamp channel or jack, bad interconnect or speaker cable, blown speaker driver and even a carbon or other compound build up on a preamp control.
     A good approach is to try and narrow down the cause of the issue by a process of elimination or ruling out possible causes of the problem in a methodical manner, beginning with the end of the signal chain and working backwards or upstream.  Here's how it works:
1.  Begin by connecting the right speaker wire coming from your amp to the left speaker and the left speaker wire coming from your amp to the right speaker.  If the problem follows the switch ( the opposite speaker now is lower in volume) then the speakers are okay but a speaker cable, or another issue further upstream, is the likely culprit.
 
2.  If a new speaker wire or pair of wires don't solve your problem, then the problem likely lies upstream.  You can test this by connecting the left interconnect cable coming from your preamp's output to your amp's right channel input and the right ic cable coming from your preamp's output to your amp's left channel input.  If the problem follows the switch (the opposite speaker now is lower in volume) the ics are okay but a preamp or amp channel or jack may be faulty.

     This process can help you isolate the issue or at least rule out some common sources of the problem. Of course, this process may ultimately require you to bring your preamp, amp or a source component in for inspection and possible repairs. 

Best wishes,
   Tim

Thanks Tim for your advise. As it happens, I just changed speakers, and then I notice the imbalance between the two mid/high frequency panels of the Mini Maggies. Everything is the same and the system was working just fine. Same source, rca cables, speakers cables, power cables, speakers. So I think the problem lies in the mid/high panel. But I am not sure what could it be.   

The mini maggies are dipoles and very sensitive to position.  Were the speakers they replaced also dipoles?  Is the proximity of the left and right channel mid/high panels to the walls similar (e.g., is one much closer to a wall or corner than the other)?  To check if placement might be a factor, keep all of the connections the same but switch the speakers left/right.  If the same side is still lower in volume then the imbalance is likely to be caused by speaker position.  Keep in mind also that the crossover point between the bass panel and the mid/high panels is relatively high so if the bass panel is sited more closely to one mid/high panel than the other that may also contribute to a perceived imbalance.