correct. It was Shure back in the 50's that decided there should be 4 pins to a stereo cart, when 3 is all that is needed. When right and left grounds are summed at the cart, there is less "noise" due to all grounds have exactly the same potential to ground.
If only three pins how do you deal with a phase inverting phono stage? They do exist.
That may be true for your amp, but it's not true for mine. The phono RCA sockets are isolated from the chassis, and yes, it does matter if the isolation is defeated.
Thanks that's interesting.
When the two return wires ("grounds") are shorted at the cartridge the return current for the generators of both channels flows through the same wire- which at the very least will degrade the channel separation. There are, as I said, other potential issues too which is why no manufacturers wire their cartridges that way and have not done so since the earliest days of stereo, and why early design luminaries like Marshall Leach insisted on keeping the channel grounds separate all the way through the cartridge preamp. Common impedances in grounds are something that should be avoided in stereo applications if at all possible.
