Magnetic turntable bearing

[Aengus]

... a lot of work.

That's why we're all waiting for you to do it.

Regards.

Aengus

[slbender]

Hi All,

I've only read the first ten pages of this thread so far, but I'd like to add a note that I own an older (circa: 1970-1975) belt drive, aluminum platter turntable on a plastic base (Not a really expensive or high end BDTT) from a maker who has been in the business for thirty or forty years now.

This 1970's BDTT has a dual ring magnet bearing under the fairly light weight aluminum platter. The ring magnets OD are approximately the size of an LP's record label and ID about 1 inch smaller. While I've never measured it, I guess the platter is suspended some 2 - 4 mm to unload the center bearing when a rubber mat and LP are in place.


-Steven L. Bender, Designer of Vintage Audio Equipment

Originally Posted by YNWOAN

YNWOAN Said in 2007 -

I notice in this months Hi-Fi+ that Clearaudio have produced a turntable using a similiar (in concept, but different in detail) bearing. I was not at all aware that any 'reasonably' priced turntable had employed this principal. The bearing experiments are only a small element of a much larger project to engineer a whole turntable. I have already done this a couple of times but am intending to approach this new design from first principles. Like Clearaudio I intend to use a low mass acrylic platter (lower than Clearaudio though), although every other aspect will be quite different. I notice that Clearaudio have used a ceramic bearing shaft to stop it from conducting the magnetic field. The bearing in my current design (Linn main bearing) does indeed conduct the magnetic field generated by my magnetic bearing, but I believe this to be irelevant to performance - leakage from the spindle is very low and has no measurable effect on the cartridge that I am aware of. I am pleased however, that Hi-Fi+ seem to hear very much the same improvements I reported.

[YNWOAN]

Hmm...interesting; I'm not aware of the design you mention (though no doubt you are correct). What is the make and model of the turntable please? Presumably it uses ferrite magnets?

[ictmanager]

Magnets....Sheffield...Magnets...Sheffield...

I read all the posts on this thread with great interest last night for a couple of hours....after I had looked up 'magnetic turntable bearing' on google...
Three things amaze me.

Firstly, I am very impressed with everybody's interest in the subject....I had thought I was alone!

Secondly, yesterday, after a few weeks of experimenting, I had managed to use mag lev on a Linn Sondek LP12, which, although it is alternately cast as an angel or a villain in the world of hifi, certainly has, in its natural form, a really musical toe tapping ability. For a few months now, a) because I am on a budget, and b) because I have engineering skills and can't ever leave well alone, I have been rebuilding my LP12 with:
1. a CAD designed water-cut single piece titanium subchassis & arm mount,
2. a CAD redesigned thicker water-cut stainless steel top plate,
3. new 7pm motor position,
4. new external & internal electronics,
5. thicker & more rigid higher tensile steel bolt & locknut components,
6. machined corian armboard,
7. machined corian baseplate,
8. lathe turned dural thickened bearing housing,
9. silicon or rubber rings on crucial parts to damp resonances,
10. molybdenum sulphide greased ruby motor bearing in phosphor bronze bearing housing,
11. laser cut and hand finished acetyl arm pillar mounted cradle for the armrest,
12. thick water-cut stainless steel motor mounting,
13. two-part mag lev ring bearing on main bearing, relieving thrust plate pressure and consequent reduction of friction & noise,
14. solid silver wiring throughout,
15. renovation of rosewood plinth,
16. rebuilding of internal hidden elements of plinth (eg internal mahogany top-plate supports)
17. other minor aspects....polishing of bearing shaft tip, etc...
and it is sounding SO good.....

Thirdly, when reading the thread, I notice that a few of you had talked about living in the UK, in Sheffield, in S11 or S7.
When I was a young guy, I remember Sheffield was world-famous for its steel works and I remember drinking Magnet ale...in fact the famous Sheffield United football team fans' song refers to 'Magnet' ale produced locally by John Smith's Brewery, a packet of Woodbines cigarettes, a pinch of snuff(tobacco), a night out in Sheffield and a greasy chip butty.

The full lyrics to Sheffield United's Greasy Chip Butty song are:

You fill up my senses Like a gallon of Magnet
Like packet of Woodbines
Like a good pinch of snuff
Like night out in Sheffield
Like a greasy chip butty
Like Sheffield United Come thrill me again....
Na Na Naa Naa Naaaaa, Oooooooh!"

Recognise it?

Well the thing is...
I was born in Sheffield S11 too...and lived there until I was 17....
There MUST have been something in the water....
:-)

[sq225917]

could be....

(currently S11)

[andyr]

Originally Posted by ictmanager

Secondly, yesterday, after a few weeks of experimenting, I had managed to use mag lev on a Linn Sondek LP12, which, although it is alternately cast as an angel or a villain in the world of hifi, certainly has, in its natural form, a really musical toe tapping ability. For a few months now, a) because I am on a budget, and b) because I have engineering skills and can't ever leave well alone, I have been rebuilding my LP12 with:
1. a CAD designed water-cut single piece titanium subchassis & arm mount,
2. a CAD redesigned thicker water-cut stainless steel top plate,
3. new 7pm motor position,
4. new external & internal electronics,
5. thicker & more rigid higher tensile steel bolt & locknut components,
6. machined corian armboard,
7. machined corian baseplate,
8. lathe turned dural thickened bearing housing,
9. silicon or rubber rings on crucial parts to damp resonances,
10. molybdenum sulphide greased ruby motor bearing in phosphor bronze bearing housing,
11. laser cut and hand finished acetyl arm pillar mounted cradle for the armrest,
12. thick water-cut stainless steel motor mounting,
13. two-part mag lev ring bearing on main bearing, relieving thrust plate pressure and consequent reduction of friction & noise,
14. solid silver wiring throughout,
15. renovation of rosewood plinth,
16. rebuilding of internal hidden elements of plinth (eg internal mahogany top-plate supports)
17. other minor aspects....polishing of bearing shaft tip, etc...

and it is sounding SO good.....

Impressive, mate. Can you tell me more about your mag-lev ring-bearing ... it's something I've been thinking about doing ever since I saw YNWOAN's post on (I think) PFM, a couple of years ago.

I'd also be interested to know what made you decide on #2 - in comparison, say, to a CF top-plate? Does your new top-plate use the same fixing bolts/ screws as the stock one? And what does the extra thickness deliver?

And I have #18 for you - but you need access to a sophisticated (CNC?) lathe. That is, to get both the inner & outer platters dynamically balanced!

An Aussie on Stereo Net Australia (SNA) had this done and, on the basis of his review, I decided to get mine done. Haven't got them back from the guy, yet, though (so I'm vinyl-less ATM).

Regards,

Andy

[sq225917]

ictmanager, your post is nothing without pics... ;-)

[bappe]

Hi Guys,

I have read parts of this thread with great interest!
Me and a few friends made an experiment with a DIY Platine Verdier about 20 years ago and came to the conclusion that it sounded better with the platter resting on the ball than not. Better dynamics in the lower registers and an overall more stable presentation was the result from the second the ball was in place. I do not know how much weight that was put on the ball but it was not much at all, we are talking about a lot less than 100g here .
Reading through a few posts in this thread got me thinking, if mechanical grounding is so important maybe a zero play bearing like the one used in the Well Tempered Record Player (without the bottom ball though) can be used to good effect here. A non inverted bearing with the sleeve replaced by two V-shaped pieces of POM would be a good start. If the force from the belt is not enough to bias the bearing this could be done by small modifications to the magnet circuit. One could either tilt the lower magnet plate down slightly on the side towards the motor or simply remove a few magnets on that side.


BR,
Anders

[kach22i]

Nice thread, I have not read all of it, mostly looked at the pictures.

Keep up the good work.

.....................back to reading what I skimmed over.

[Thesoundmen]

interesting thread, also because I am planning to make my own TT.

I had drawn a lot of plans with a normal bearing like we all now them with the ceramic bal at the button.

Than I saw this thread and began thinking about it, this must be the way to go I thought.

So after some searching I saw that the Da Vinci Audio Gabriel AAS MK2 also used a magnetic bearing.

Here is a photo of that one :



Could some one help with calculating how much magnets you would need for a 20 kilo platter ?

Thanks