My 7 cents, inflation mind you and late post, its just something in your wire wasn't going to earth, wasn't really grounded.
Electricity as much as we know, still has it's mysterious ways. I don't know the following to be true, just experienced it. I've had poor grounds with 1 TT hooking the other TT to a separate ground on a different device. I get a hum. I know power supply hungry device grounds can resist since it
"s Impedance is already at the max. repelling, pushing at capacity, I.e. a big transfomer, power conditioner, etc. I think because I'm ground to it but further out same circuit, different wall plug. But making sure end to end both TT grounds are solid and hooking to the same preamp ground, well fine! And that preamp can be hooked into a floating grounded transformer, but they're all using the same ground.
I've also read that (though I've often hooked up to an integrated amp, but not now, have separated amps) in the computer world, do not ground separate devices to same ground that is the main power source?
I don't know, but I've only had hum hooking up two TT"s, 1 TT getting a hum when that TT is hooked plugged into an adjacent out let 6 feet away and I use another devices ground. It's only let me to believe that whatever the signal, it wants to be grounded to the same circuit in my house...and ive messed with this many times, many combos, and only can say that I'm 100 percent and tested outlets away from each other but on the same circuit. Or used power conditioners. My only solvable no noise, was the two TTs on the same preamp ground which goes straight to outlet or I can even use both outlets (2, same box) but using same ground. I can even use a heavy conditioner or floating transformer plugged into 1 of 2.of that box but both TTs grounded to that preamp, fine.
I'm quite sure someone with expertise in electrical can explain why. I'm just inclined to say the hum your getting is almost either interference by using same preamp/ amp but, the 2nd TT or one of them isn't truly grounded, or as said, its a signal thang?. Because too, I've had a few times in my life a singular TTs that sounded fine, no hum and I've found ground wires on them disconnected or better said poorly connected to ground?. It wasnt until I added a new device to that IA main source that I got a hum, even though I screwed ground tightly, see its grounded? I know this post is muddy. But earth/and water great grounds.
