I had a bad hum from a VPI PLC power line conditioner until I relocated it away from the turntable and preamps. The SDS is OK.
It should seem that five or six inches of unshielded cable wouldn't pick up that much AC interference unless there were a really big source of interference nearby. Could there be a high voltage line in the wall behind the turntable? Doesn't sound like it if you've had this problem in two different apartments. What about the turntable motor (God forbid)? Is there still hum when it is unplugged? Presumably you've observed the hum when the motor hasn't been running.
Perhaps one of your plugs is improperly wired, e.g., the plug on the end of the exposed cable that goes into the junction box and/or the junction box itself. Is there some way to plug your arm cable into your interconnect, bypassing the junction box? (This may require some kind of adaptor.) Laborious though it may be, consider connecting your cartridge directly to the phono preamp with another set of leads (maybe cheapos from Radio Shack) that don't go through the tonearm at all. Of course, you couldn't play a record, but you can still see if there is hum while the arm sits on its rest. This test would isolate the cabling between the cartridge and the junction box, as well as your interconnect.
If all this results in a reaffirmation that the exposed wire needs to be shielded, try getting some shielding material (webbing) from Radio Shack to wrap the cable, and think about how to ground it. Perhaps the manufacturer could recommend a way to do this without interfering with the mobility of the tonearm. Good luck.
It should seem that five or six inches of unshielded cable wouldn't pick up that much AC interference unless there were a really big source of interference nearby. Could there be a high voltage line in the wall behind the turntable? Doesn't sound like it if you've had this problem in two different apartments. What about the turntable motor (God forbid)? Is there still hum when it is unplugged? Presumably you've observed the hum when the motor hasn't been running.
Perhaps one of your plugs is improperly wired, e.g., the plug on the end of the exposed cable that goes into the junction box and/or the junction box itself. Is there some way to plug your arm cable into your interconnect, bypassing the junction box? (This may require some kind of adaptor.) Laborious though it may be, consider connecting your cartridge directly to the phono preamp with another set of leads (maybe cheapos from Radio Shack) that don't go through the tonearm at all. Of course, you couldn't play a record, but you can still see if there is hum while the arm sits on its rest. This test would isolate the cabling between the cartridge and the junction box, as well as your interconnect.
If all this results in a reaffirmation that the exposed wire needs to be shielded, try getting some shielding material (webbing) from Radio Shack to wrap the cable, and think about how to ground it. Perhaps the manufacturer could recommend a way to do this without interfering with the mobility of the tonearm. Good luck.