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In Reply to: RE: Why turntable bearing shaft and spindle machined as one piece? posted by Lew on October 24, 2016 at 07:25:54
Lew: "So, how would you effectively decouple the spindle from the bearing, in a world where gravity is "the law"?"Make the spindle part of the platter but not the bearing shaft? The kind that has a sub-platter is rather easy. For example, look at the video below of the Bergmann turntable. I hope it illustrates my point.
That also brings me to an observation about Lenco users adding another platter on top reported positive result is partly because of the decoupling of the spindle from the bearing. Similarly some German users like adding an acrylic platter on top of a Micro-Seiki turtable may have similar benefit.
=============================================Lew: "Other than maglev, what do you suggest?"
Mag-lev is a good way to lessen the mass of the platter (Continuum does that) but I think most still have the bearing bottom end touching the thrust pad instead of floating that might affect VTA. I saw a video of a Clearaudio mag-lev bearing that the platter can be pushed down and spring back up when released. Not sure if that's vertically stable when playing a record. It might. I don't know.
Airbearing is completely isolated. Whether that thin layer of air is rigid enough to not have vertical movement is up for debate. I'll leave that to the airbearing experts.
Edits: 10/24/16 10/24/16Follow Ups:
Here are two examples of after-market modifications that seem to aim at the same thing as that Bergmann platter:
http://www.arche-headshell.de/accessoires/sdp-the-sonically-most-effective-upgrade-for-every-turntable/
http://tinypic.com/view.php?pic=10ge1pt&s=8
Plato65: "Here are two examples of after-market modifications that seem to aim at the same thing as that Bergmann platter":
SDP platter mod & Garrard 401 platter mod
Thanks for the examples. That German website is what I was talking about in my reply to Lew.
Several other turntables over the last few decades have mounted the platter on top of a smaller subplatter that is part of the spindle and bearing. (Now that I see the video, I understand better what you were talking about.) I think my old Thorens TD125 was like that, and there are more that I cannot name off hand, maybe including the original AR XA. If one were inclined to pick nits,one could say that since the actual platter has a large physical contact area with the carrier subplatter, spurious energy could easily be transmitted into it from the subplatter, using the method you seem to admire. The SP10 Mk2 bolts the "top platter" (in your parlance) to a smaller carrier, using 3 machine screws. This is good for structural stability but further enhances energy transfer, if one is terribly worried about that. On the maglev side, you are neglecting the Verdier, where the vertical suspension is entirely magnetic, and the massive magnets mostly interdict unwanted up or down motion of the platter that could effect VTA. Some love the Verdier, some do not. IMO, in a belt-drive, there is more issue with motor vibration being transferred into the platter via the belt, vs energy from the bearing friction.
Lew: " I think my old Thorens TD125 was like that..."The 125 (or 160 or Linn LP12 for that matter) uses a subplatter but the top platter has a huge hole that allows the subplatter to be part of the whole surface where the record touches so the spindle is still a part of the bearing shaft. I owned one before so I remember its construction.So it's not the genre I have in mind.
Here's an inverted bearing as an example that I question about noise... Notice how close the thrust pad is to the record...
Edits: 10/24/16
My Rockport Capella II with standard ruby bearing has a flat top (no spindle) sub-platter, which the main platter with its spindle sits on. However, since the main platter is connected to the sub-platter metal to metal with 6 bolts , I can't imagine this arrangement has any effect on decoupling the bearing noise!
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