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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 4 responses by au_lait

au_lait OP
335 posts
 
No I don't hear it on the recordings really, it's far too faint for that, or I haven't tried any music quiet enough to notice. I'm talking solely about when there is no music playing (so maybe it just doesn't matter) ad it's loudest while resting. As I pivot the arm closer to the center of the platter, the hum lessens, almost as if it's on a fader. Will try new styles this eve and see. Thank you all for the advice!
au_lait OP
335 posts
 
@chakster Yeah I have done/checked every one of those basic tests and have narrowed it down. It's not a ground issue - my phono cable grounded to either phonostage or preamp is all good. Its a very quiet hum (not buzz) and it really only happens when the arm is resting. Not hearing through the speakers unless its really loud, BUT I am digitizing lots of vinyl and I hear it a bit through the ADC on headpones. It's not the end of the world, of course, and I will try another cart tonight. Just curious if anyone had experienced this before. Maybe I lowered my noise floor to the point that I've uncovered something that was masked before?

Cartridge: Nagaoka MP150 (Will try with Zu DL103 tonight)
Mats: Nagaoka Crystal, will try with Herbie's, TMM Monitor, Rubber/Cork mix tonight
au_lait OP
335 posts
 
Problem found. A dimmer on the other side of the house. It’s not on the same line as the whole system is on its own dedicated. I guess the dimmer causes a ground loop since they’re on the same bar at the box? When on: buzz. When off: dead quiet. Anyway, dimmer removed, problem solved for good!

Sorry @chakster for hassling you about the cartridge LOL
au_lait OP
335 posts
 
@tomic601 Yes, leg, thanks Jim, pardon my layman’s terms! But now that I think of it, not sure it has to do with what leg. A month ago my front end and amps were on 2 separate lines on the same leg at the panel, but now since moving my front end across the room, I ran another line to that location using a breaker slot on the other leg, but still had the buzz. The hash only cleaned up once the dimmer was gone. Noise floor is pretty damn quiet now, but I’ll try your suggestion too. It’s an old house and the panel is a mess with loads of tandem breakers.
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