Ok to adjust balance to achieve center vocal image?

Lots of ideas here.  If it were me, easily my first theory — especially since you said it was not previously doing this, presumably in the same room and with the same/similar gear — would be that my azimuth had fallen into a leaning position and the stylus was favoring one channel by a smidge.  Lots of ways to check and adjust that, depending on your gear.  Worth a few minutes on googling “turntable ... azimuth.”  My second theory would be what someone above said: my room is such that I need to bring the weak side speaker an inch or two closer to the listening spot.  This can be such an easy fix that it feels like cheating.  

Wayward imagery can be caused many things that may drive mad someone. I would include the following for checking,
Use a cd player to confirm that image is center.
All Recordings are not the same, check with a test record for center voiceNot matched tubes in phono stage, swap tubes L/R to check that image is the same or not.
Align correctly your cartridge, overhung, hta, antiskating (use low), azimuth.....
In most of cases your answer is there.
Speaker positioning, toe in-out, same tweeter axis, moving front to back as rooms are not perfect.Swap L/R cabling.

G

Lots of great ideas here to try by process of elimination. I will get to work with swapping cables, speakers, tubes and adjusting VTA and cartridge set up. Thank you all for the ideas. Much appreciated!!

Hello,
Tubes are a fast wearable item compared to caps. The Rouge preamps have an elaborate balance system. I would think it is for this purpose. Besides, who says you cannot listen the way you prefer to listen. I have a Shiit Loki equalizer for changing the sound on our “remastered” or bastardized recordings. What’s next, people saying power cables make an audible difference? They definitely do unless you bought your system at a truck stop. If it sounds good to you that is all that matters. 

Azimuth will not affect channel  balance, it will affect tracking and record wear but not balance.  Nor will VTA, but never hurts to double check cart alignment especailly if you haven’t in a while for overall sonics.  I would check all cable connections including your cartridge pins and obviously tubes.

But do not be afraid to use your balance control, and adjust speaker toe in and distance from the front wall where the balance is off.   Annoying I know!