Exposed tonearm cable source of hum??

Thanks to all for your input.

The previous post is certainly correct that it would be much better to provide the name of the arm manufacturer, but this forum is such a hotbed for rumors which can be commercially damaging that I prefer to posit the question generically (even if it means I am prevented from getting information which might solve the problem). Sorry for making you all stab in the dark.

I have a custom MDF stand that has the turntable and turntable motor on top sitting on two inches of MDF, the pre-amp below it on next shelf, transport below pre-amp on next shelf, processor below transport on next shelf, phono pre-amp below processor, and PS Audio 300 on bottom. I have monoblock amps that are 20 ft. from the source components and in another room. There are no interconnects or power cords dangling freely and visibly behind or under the components -- all are ported through small holes behind the components and thus hidden behind the component shelf (and thus somewhat sequestered from the components). I had the turntable on a totally different shelf in another state with completely different components (no PS Audio, for example) and had exactly the same problem. I also ran the identical turntable / arm / cartridge into the phono stage of a CAT pre-amp for two years with no hum, but the CAT, which has no step-up transformer, has roughly twenty decibels less gain than the Rowland Cadence I am now using. I've tried floating the ground, star-grounding, filters, moving components around, reconnecting the leads to the cartridge, plugging compenents onto different A/C lines, using different interconnects from the junction box to the phono preamp, but nothing helped. If the loop is disconnected from the junction box, I get zero hum, regardless of volume setting. The problem arises only when I connect the "loop" to the junction box, which leads me to focus on the exposed loop becoming a problem if used with a high-gain phono stage.

Thanks again.

One more thing ... the problem exists whether the turntable motor is on or off, and regardless of the position of the tonearm -- these variables do not change the nature or quantity of the hum.

Thanks.

How do you know the hum isn't from upstream of the exposed cable, like from the cartridge or in the arm?

The previous post makes a good point. I had reconnected the leads to the cartridge with the thought that these connections may be the problem, but it changd nothing. What I did not do until yesterday, however, was try switching the leads around a bit. It would seem that the Blue Negative tonearm cable lead is the source of the problem inasmuch as the system has no hum until that lead is connected to the cartridge, regardless of which post on the cartridge it is connected to (I switched the white positive / blue negative to the other channel and also wired the cartridge out of phase with the negatives connected to the positives). As soon as the blue lead hits a post on the cartridge, I get hum. I also connected the cartridge leads to a different cartridge, and the hum is still there (albeit of a slightly different noise signature). I would be prepared, now, to conclude that I have a bad blue lead, but have to, at this point, get back to the manufacturers with this new information.

Thanks to all of you for your help.

Do this diagnostic test, if you haven't already, just to confirm your suspicions: Try manually introducing a temporary shield around each of A) The exposed wire, B) The tonearm, and C) The cartridge/headshell, simply by surrounding the part in question within your cupped hands while monitoring through the speakers at a revealing volume (or maybe even better yet through headphones, if possible). If the hum is being induced from outside interference in any of these parts, the level should be noticeably attenuated when you cover it up in this way. On the other hand, if there's no changes at all, I would move on to suspecting something internal...