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Problems earthing a tone arm on a TD125...any suggestions?

neiljadman

neiljadman

Senior Member
OK, I have a nice TD125 that I got with no arm or armboard. It seems to be good and holds a rock steady speed and the bearing and motor are silent. So I cut an arm board and mounted a Linn Basik + arm that i have around to try it out before shelling out for something better.

The only problem is an annoying hum.

  1. The arm is connected to the phono pre amp via a non-Linn cable which as an earth at the amp end, but no way of earthing to the chassis at the DIN end.
  2. The floating part of the chassis is earthed to the main fixed chassis, and
  3. I have run an additional earth lead from the main chassis to the same grounding post on the pre.

I was expecting this to give me a good result, but I've tried linking other part of the chassis to earth and breaking the link between the two chassis parts- all to no effect. I still can't get rid of the hum.

Does anyone have any insights as to what I may have dome wrong?

Thanks in advance for your suggestions, Neil
 
This may not be of help, but Linn suggested years ago that the arm should be earthed to the deck for safety reasons. The deck should be earthed to the mains and the arm earth wire at the phono plug end should be connected (or not) for minimum hum...

Thorens (with their arms) used to earth their decks via one of the signal screens (as did my Dual 1229 and 701) as I recall..

Try removing the arm board, reconnect the arm cable and see if there's hum with the arm away from the deck. If there's no hum, we'll look again, but if there is, beg or borrow the dosh to get a "T" cable from Linn, as it improves all their arms...
 
Well, I can certainly try taking the chassis earth to mains and will get the benefit of new mains cable at the time time. I can probably rig the arm to earth also.

But a T-cable is out of the question - since the 125 cost me $25 and and the arm has been sitting since a long ago upgrade mad the cable I have is also a Silver cable. I'll see how the mains earthing goes - thanks for the tip.
 
Thanks DJSR - problem now solved - unconventional but it works for me. An just in case anyone else needs it - here's my earthing configuration:
  1. A new 3 core mains cable taking both parts of the chassis to mains earth.
  2. Tonearm cable to grounding post on pre-amp
  3. Additional chassis earth cable to grounding post on pre-amp
Problem solved and there's silence!
 
Glad I could help. TD125's are growing in stature now in the UK, but watch for wobbly main bearings in mk2's.
 
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