Balance control?

Starting with the recorded vinyl record:

Not all have symmetrical balance.

Room placement, toe in, wall reflections can all influence balance.

At the turntable/ tonearm:

Antiskate, correct orientation of cartridge, Azimuth all will have a large influence. One cannot expect exact channel balance with inexact cartridge set up incorrect antiskate or azimuth.

The cartridge:

Ultra inexpensive cartridges cannot be expected to be as precisely accurate with regard to cartridge body to internal generator alignment. Costs are cut. So too are corners in quality..

My post was general not specific to one individual member. I hope you solve your problem.

That is an excellent suggestion wlutke. No guesswork. Measure cartridge channel balance at phono leads. Measure cartridge channel balance at phono eq outputs. Measure preamp channel balance at preamp output. Measure channel balance at power amp outputs.

Measure at every stage for channel balance. The only other factors are room/speaker interface( measure with Sound Pressure Gauge at listening position?) or get ears checked for equal hearing response in each ear.