Turntable troubles

Sounds like it (speakers/cartridge) could be out of phase, if you just hooked up the speakers or cartridge recently check that your wires(red +black) (red,green,blue,white) are correct. If you haven't messed with anything recently it could probably be a number of less easy fixes. I'm not sure where you would start though to be honest.

Regards,
Bill

Shut your amp off and go to just 1 of your speakers. Reverse the speaker cable connections. (+ to - and - to +). Just do this for 1 speaker only and only at the speaker end. (You can do it at the amp if its easier to access. Just don't do both ends). If the vocals go back to the centre after you do this, recheck your speaker cable connections; you made a mistake hooking them up. I know you think its a TT issue. It may be, but rule this out first.

Do other sources behave the same or is this just an issue with vinyl playback?

If this condition only happens with vinyl, Switch your left and right leads from the table to he preamp so that the left channel of the table is playing through the right channel of the preamp. If the balance swings to the left channel, the problem is with the cartridge. If the balance still favors the right channel, the issue is with your electronics.

I had this problem. Thought maybe it was my needle or anti skate. Turned out to be a bad cold soldered joint in a RCA cable. You have to be very systematic in trying to diagnose and isolate the problem. Good luck