Tone control altered Balance ?

I don't know how the bass control is implemented in that NAD amplifier, but if the control is a dual potentiometer then left/right tracking (balance) is never going to be great. I wrote blog post on the subject here, focussed on volume controls but applicable anywhere a dual pot is used. You may need to adjust the balance after changing other settings.

See an audiologist.

Did not realize this through loudspeaker

check your earphones or something is going on in your amps hedphone out.

G

Hey,
Unfortunately the parts used in tone controls are often not as good as parts used in the rest of the audio chain, even less so in the headphone amp sections.  All sorts of things could be going wrong.

e