Exposed tonearm cable source of hum??

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.

Hello,

I think if you would specify which arm you are using, you are more likely to get specific ideas from other owners of the same. As it stands, all anybody here can do is shoot in the dark the hum problems that they have had and what they did to fix it. But most likely your problem is very specific to what you are using. The more details you can give to the group, the more likely your problem will be resolved.

I have a Clearaudio Ref TT with the TQI arm and this too has an unshielded 4" loop of wire over the top and then another 6" or so of wire to the terminals. A shielded tonearm cable then goes to the phono stage. And I have moved line stages (ARC and BAT) and phono stages (BAT and Aesthetix), CD players and DACs (Tube and SS) next to, underneath, etc., this TT and no hum at all. And power cords are going all over the place! So I doubt that it is this small loop of unshielded wire causing you all the pain. It sounds more like a not very solid tonearm lead connection, potential internal short or poor grounding.

I also have a Versa 2 TT which too has a 5-6" loop of unshielded wire above the arm and I have heard of no reports of hum from people out there either. If moving the TT across the room for a simple test does not alleviate this problem, I would suspect that the problem is internal to the arm's wiring and termination .... and not the small length of unshielded wires.

John

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?