Sorry if this has been covered already, but I have a Technics SL-QD33 turntable that used to play just fine -- then out of nowhere the sound has become... overblown. The bass notes especially but in general it sounds like it's coming into the reciever too loud. I changed the cartridge, I changed the rca cables, I tested the ground, I listened to it just through headphones... all to no avail. the only thing I didn't do it plug it into another receiver as this is the only one I have that will play phono.
There is no explanation in your explanation for the cartridge to over load the phono section. Most likely it is a capacitor that has begun to go bad or a resistor that has drifted in value. Try another receiver and listen for better results.