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Thread: Weighted pivot ... Questions

  1. #1
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

    Default Weighted pivot ... Questions

    I came across a post which mentioned placing a weight on top of a jelco pivot housing. Hugo does this I believe and it has piqued my curiosity. I understand the rationale but wouldn't the extra weight affect the ease of travel of the arm? After all the pivot turns as the arm arcs and so would any extra weight act a little like anti skating...?
    Technics SP10 mk2
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    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
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  2. #2
    Join Date: Jan 2009

    Location: Norwich

    Posts: 2,814
    I'm Hugo.

    Default

    This tweak is only suitable for arms where there is a resonant structure surrounding the pivot and absolutely not on the pivot itself - as with the Jelco SA-750 series and my FR64S. The weight therefore has absolutely no effect on the arm's movement. Look at this picture of my SA-750E and you can see that the mass damping weight sits on top of the cradle and does not go anywhere near the bearing structure:



    Do not under any circumstances think about placing any mass or weight directly on any tonearm's bearing structure or pivot, since this will only result in disaster.

  3. #3
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

    Default

    You mean like this..

    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  4. #4
    Join Date: Jan 2009

    Location: Norwich

    Posts: 2,814
    I'm Hugo.

    Default

    This tweak is only suitable for arms where there is a separate structure surrounding the pivot and absolutely not on the pivot itself - as with the Jelco SA-750 series and my FR64S. Look at this picture of my SA-750E and you can see that the mass damping weight sits on top of the cradle and does not go anywhere near the bearing structure (on these Jelcos that cradle does not touch the 'drum' housing the bearings):



    Do not under any circumstances think about placing any mass or weight directly on an arm's pivot, since this will only result in disaster (excessive bearing loads, uneven mass distribution, etc). In the case of the FR64S, the flat top of the arm structure does rotate with the arm, but it's only in the horizontal plane, and the horizontal bearings are built like bits of battleship, so adding a mass there does not influence the vertical movement of the arm tube at all.

    See http://theartofsound.net/forum/showt...721#post841721 for an explanation of why this works, in suitable tonearms.
    Last edited by Ammonite Audio; 08-03-2017 at 15:14.

  5. #5
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

    Default

    The Siggwan bearing is a little like the FR, it only moves laterally. However that housing must also be sitting on a bearing in order to rotate so maybe best not to - however the same surely applied for the FR and jelco... scratch
    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  6. #6
    Join Date: Jan 2009

    Location: Norwich

    Posts: 2,814
    I'm Hugo.

    Default

    No, the Jelco SA-750 arms are different because that cradle surrounding the bearing is fixed to the arm's base structure and does not move at all, nor does it make any contact with the bearing housing. I must stress that this tweak only applies to the SA-750 series - the cheaper SA-250 does not have this fixed supporting structure and placing a weight on top would cause damage. In the case of the FR64S, I'm confident that the horizontal bearings are specified like everything else on this arm - eg somewhat stronger than the norm, so I'm happy to take the risk.

    If we confine this discussion to Jelco SA-750 arms and their more or less identical derivatives (Audioquest, Sumiko etc), there's no risk in applying a mass damper to the top of the arm. Someone with a suspended deck might have to re-balance the suspension, but that's it.

  7. #7
    Join Date: Apr 2016

    Location: Gravesend and France

    Posts: 1,498
    I'm paul.

    Default

    This " tweak " only benefits the person selling a piece of metal to sit on top the cradle.

    Quote Originally Posted by Ammonite Acoustics View Post
    This tweak is only suitable for arms where there is a separate structure surrounding the pivot and absolutely not on the pivot itself - as with the Jelco SA-750 series and my FR64S. Look at this picture of my SA-750E and you can see that the mass damping weight sits on top of the cradle and does not go anywhere near the bearing structure (on these Jelcos that cradle does not touch the 'drum' housing the bearings):



    Do not under any circumstances think about placing any mass or weight directly on an arm's pivot, since this will only result in disaster (excessive bearing loads, uneven mass distribution, etc). In the case of the FR64S, the flat top of the arm structure does rotate with the arm, but it's only in the horizontal plane, and the horizontal bearings are built like bits of battleship, so adding a mass there does not influence the vertical movement of the arm tube at all.

    See http://theartofsound.net/forum/showt...721#post841721 for an explanation of why this works, in suitable tonearms.
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  8. #8
    Join Date: Jan 2009

    Location: Norwich

    Posts: 2,814
    I'm Hugo.

    Default

    Thank you for that, but who is selling it? Speedy Steve made me one and that is all.

  9. #9
    Join Date: Dec 2015

    Location: Alicante. Spain.

    Posts: 1,885
    I'm Adrian.

    Default

    Thanks Hugo, I saw your post on speedy Steve's thread and it got me interested. But I'll take your advice and leave well alone.
    Technics SP10 mk2
    Jan Allaerts MC 1 Boron mk1 cart
    Miyajima Shilabe cart
    Hashimoto HM-X SUT
    Siggwan (gimballed not unipivot) Cocobola 12"
    Aurorasound Vida LCR Phonostage
    The Truth linestage
    Dave Slagle Autoformer Volume Controller
    Cary 805c SET amps
    Audio Note ANe-SPX speakers
    Townshend Isolda speaker cables
    Cardas Golden Presence interconnects

  10. #10
    Join Date: Aug 2016

    Location: Manchester

    Posts: 122
    I'm Nick.

    Thumbs up

    Oh I do love this site

    Just tried this little trick on my 750db and it has made a notable difference.

    Cheers Hugo

    Nick.

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