Left/right channel imbalance

It is probably cartridge calibration at the factory, the best cartridges are selected for a proper channel balance between L and R. Some cheaper cartridges have imbalance by default and the best way is to have a preamp with separate L and R volume control. 

But first check the anti-skating with Test Record. 
And set up the azimuth correctly with a shell with azimuth settings. 

  

Swap in a cheap cartridge and compare the balance.. It’s probably your cartridge.  Replace it or use the balance control to even it out.

I had one once that I loved but the imbalance drove me nuts.. I gave it away, because adjusting the balance also drove me nuts..