malmc02
The hum exists even with the cartridge not connected to the system ...That really doesn't matter. Have you tried a cartridge other than the Ortofon Cadenza Black? You need to rule out the cartridge as a source of the hum, and merely testing the phono preamp with no load attached doesn't satisfy that.
... and issue has been there for a long time.But: Was this issue always there? Did you previously get satisfactory results? That is the million dollar question.