Phono Stage Hum

Connection: Music Hall TT with Grado Reference 1 MM Cartridge to Jolida JD9 Phone Stage to line input on my integrated amp. Got classic Ground Loop Hum when connecting the TT to the high level inputs on the JD9, less noticeable when connecting to the low level inputs. Jolida very helpful, tried a couple of traditional ground loop fixes, hum is still there. Connect TT directly to the integrated amp phono input using the same Kimber Hero interconnects. No hum. Plug Kimbers back into the JD9, hum is back.

Go digging through junk box, swap out the Kimbers with some 30 year old plastic Red / yellow Radio Shack interconnects, no hum. Sound isn't that great, but not too bad. What is going on? Are the Kimber Hero's (tried woth Ultraplate Blacks and WBT's) not shielded well enough for a TT to Phono stage interconnect? Am I just masking the hum with the cheapo interconnects?