The Grado cartridges are a moving iron design and have always been notorious for hum problems with turntables/tonearms that have less than ideal shielding of the motor. This has been well documented. I was a Grado dealer for many, many years and know this first hand.
I'm not sure that even reducing the output voltage of the cartridge will work unless you want to shield the motor somehow on your Thorens.
IMHO, I would move to a different cartridge, (or spend the time and money to shield the motor).
I'm not sure that even reducing the output voltage of the cartridge will work unless you want to shield the motor somehow on your Thorens.
IMHO, I would move to a different cartridge, (or spend the time and money to shield the motor).