"" The output of a cartridge is in principle balanced UNTIL one side (usually the negative) is connected to ground. This may happen at the cartridge (where the (-) side of one channel is connected to a magnetic screen around the cartridge internal wiring..""
Some cartridges came with 3 not 4 pin connectors. I can't find out a " vintage " thread where the normal statement that the cartridge is a balanced design was questioned by serious high technical knowledge oriented Agoners and if I remember J.Carr posted down there and the final conclusion was that in reality the cartridge is not a true balanced design.
I have not the elements about but that " cartridge balanced " could be a little controversiallly. I think that other Agoner in that thread was kirkus along dgarretson. I wish I could find out because is of true ineterest for all of us. Unfortunatelly I can't remember the technoical foundation about but exist somewhere.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.