Sorry for jumping in late so late, but I've lived thru some strange grounding problems, too, and have some different ideas to try.
Since you have dedicated lines, we can assume that there is ground at the outlet. Having never seen Naim gear, have you checked that the 3 prong plug wiring is all attached within the case, or could the ground be "floating" in the Naim?
You have had a ground lead connected to the Orbe with no effect. Have you tried grounding the Orbe and the Graham at the same time, first to each other and then both to the preamp? (Even though there isn't a screw on the arm post, temporarily you could use a cable tie, rubber band or "twistie" just to keep it on there, making contact.
A preamp of mine had a low level hum problem due, somehow, to the brass feet digging in to the metal rack. I had to ground my rack to the preamp! Hum gone! I never would have believed it.
Have you unplugged your AC to the turntable to test any difference in hum? The fact that you can feel a small bit of current in the arm makes me wonder if the turntable/motor wiring is completely insulated from the rest of the base (metal, I'm guessing). Or if you have the outboard power supply, if there might be some sort of leakage that the gain in the phono stage is picking up on.
Good Luck!
Todd
Since you have dedicated lines, we can assume that there is ground at the outlet. Having never seen Naim gear, have you checked that the 3 prong plug wiring is all attached within the case, or could the ground be "floating" in the Naim?
You have had a ground lead connected to the Orbe with no effect. Have you tried grounding the Orbe and the Graham at the same time, first to each other and then both to the preamp? (Even though there isn't a screw on the arm post, temporarily you could use a cable tie, rubber band or "twistie" just to keep it on there, making contact.
A preamp of mine had a low level hum problem due, somehow, to the brass feet digging in to the metal rack. I had to ground my rack to the preamp! Hum gone! I never would have believed it.
Have you unplugged your AC to the turntable to test any difference in hum? The fact that you can feel a small bit of current in the arm makes me wonder if the turntable/motor wiring is completely insulated from the rest of the base (metal, I'm guessing). Or if you have the outboard power supply, if there might be some sort of leakage that the gain in the phono stage is picking up on.
Good Luck!
Todd