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TT Hum

So... I have not noticed this through my speakers, but in headphones; I get a low hum depending on the location of my tonearm. When it’s resting it’s noticeable, but when I move it to cue the hum reduces. Basically, the closer to the center of the platter the less the hum. I have an SL1200, and the power supply is offboard so it shouldn’t be anything under the platter, there is no transformer, etc. It’s not the ground wire from the arm (Jelco SA750D) either. My PSU and everything else is on another shelf, so I can’t see it being interference, and when moving things around it doesn’t change. The only things I can think of could be some kind of weird interference from the pitch fader (that’s the only thing even near the arm's resting position) or I’ve yet to try yet another cart/headshell. Stumped. Thoughts?
au_lait

Showing 2 responses by mijostyn

mijostyn's avatar
mijostyn
8,570 posts
 
Lewm, many cartridges have a shield inside that is grounded. Some may not. There is the noise floor of the phono section which you will hear if you turn it all the way up. But at any reasonable volume my ARC phono stage is dead quiet even with your ear right up next to the speaker.
I think the principle defect here is probably in the turntable as I have never heard of hum problems with a Nagaoka especially since it is an MM cartridge. The only cartridge I have ever had a noise problem with was a Grado which hummed as the cartridge got closer to the motor. They are notorious for this problem. 
mijostyn's avatar
mijostyn
8,570 posts
 
au_lait, when it talks like a duck and walks like a duck it is usually a duck.
The Cartridge is not well shielded and there are electronics at the right side of the table that are emitting. Make sure the cartridge body is getting grounded. You may need a cartridge with better shielding. It is not too bad and you do not hear it through your speakers so you may elect to just live with it. 
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