despotic931 said:
I imagine that with a center shaft underneath the platter that had magnets arranged radially around it with poles facing out, parallel to the platter surface, and encircled by fixed magnets with the same poles facing in, you could keep the platter centered. The trick would be eliminating any wobble caused by varying magnetic strength, and getting all the magnets aligned and fixed in place.
You could achieve a similar result with an air bearing, with the obvious tradeoffs.
With coils underneath the platter switched on/off at the right rate, you could use the permanent magnets suspending the platter as part of the motor drive.
Just my 2 cents - interesting to read about what you guys are up to.
The strength of the magnetic field required would be huge and certainly be a real issue for the cartridge.
The purpose of the mag lev bearing are thus: 1/ the bearing no longer 'grinds' it's point against the thrust pad - reducing noise and 2/ the closed loop is broken.
The bearing still exhibits drag as most of this is supplied by the bearing liners which are still used.
The purpose of the mag lev bearing are thus: 1/ the bearing no longer 'grinds' it's point against the thrust pad - reducing noise and 2/ the closed loop is broken.
The bearing still exhibits drag as most of this is supplied by the bearing liners which are still used.
I find the magnetic suspension and furthermore magneto-drive principle fascinating, however;
would it not be simpler and more effective to design and manufacture a better conventional bering?
Furthermore, why not mount the platter on two bearings with a vibration absorbsion ringed material between them?
And of course, I am not trying to dismiss the idea of solving the problem of magnetic turntable bearings. Some problems have a purpose and if no other, it is to make us think and explore ideas.
However, a complex solution to a problem, engineering wise, has to prove additional merrits compared to more conventional solutions.
would it not be simpler and more effective to design and manufacture a better conventional bering?
Furthermore, why not mount the platter on two bearings with a vibration absorbsion ringed material between them?
And of course, I am not trying to dismiss the idea of solving the problem of magnetic turntable bearings. Some problems have a purpose and if no other, it is to make us think and explore ideas.
However, a complex solution to a problem, engineering wise, has to prove additional merrits compared to more conventional solutions.
SaSi - what kind of a 'better' conventional bearing do you think would offer the specific benefits of a magnetic bearing? Air bearings are certainly much more elaborate constructions.
Please elaborate on the two bearings you suggest could be used to support the platter. Adding vibration absorbing rings, in the manner I interpret from your post, would add a significant level of compliance in all planes; not a quality I would consider desirable.
Magnetic bearings are really not complicated constructions. A level of fine tolerance is required in their manufacture but that is a requirement of all quality bearings. Only two extra components are required in my own implementation. Most of the problems people have encountered are due to either inappropriate choice of specific magnets or flaws in the construction method (inaccurate construction) and have nothing (in my view) to do with the concept as such.
Please elaborate on the two bearings you suggest could be used to support the platter. Adding vibration absorbing rings, in the manner I interpret from your post, would add a significant level of compliance in all planes; not a quality I would consider desirable.
Magnetic bearings are really not complicated constructions. A level of fine tolerance is required in their manufacture but that is a requirement of all quality bearings. Only two extra components are required in my own implementation. Most of the problems people have encountered are due to either inappropriate choice of specific magnets or flaws in the construction method (inaccurate construction) and have nothing (in my view) to do with the concept as such.
First, let me describe the bearing I consider "better" for the purpose.
A typical bearing (formed by an inner and outer ring with friction spheres between them) used to mount a platter to a shaft is oriented horizontaly and the "friction axis" is horizontal.
Consider an alternative bearing where the inner ring extends from below and the outer ring extends from above using the bearing spheres between them. In this case the "friction axis" is vertical.
The first case bearing will work but a heavy platter will wear out the bearing causing increased noise over time.
In the second case the friction balls better support the platter.
Now, suppose that this bearing is rather substantial in size: 3-4" inches in outer diameter and half an inch in thickness.
Now, suppose that we use two such identical bearings.
The bottom bearing rests on the plinth and form the rotating axis with a small shaft.
On top of that a rubber ring of 0.5" thickness is placed and on top of that a second bearing rests, supporting the platter.
Going back to your comment on increased compliance introduced by the vibration absorbsion ring, I agree with you that this can become an issue.
But as I see it, a magnetic suspension bearing in the center would introduce a similar effect - would it not?
In any case, this is an interesting discussion and I look forward for your comments.
Ah yes, thank you for the clarification. I see that you are describing an improved ball-race bearing. This type of bearing is not used in turntable main bearings (not in any turntables I know of any way); the main reasons being that (as you identify) they are not designed to support load tangential to the axis of rotation Also, they exhibit relatively high friction and are also noisy. By far the most common bearing consists of a shaft running in a sleeve (or sleeves), the end of the shaft bears on a single ball or has a radius and this bears against a hardened thrust pad or one made of Teflon etc.
A magnetic bearing does indeed introduce compliance but this is only in the vertical axis. It is compliance in the horizontal plane that I would consider an issue.
A magnetic bearing does indeed introduce compliance but this is only in the vertical axis. It is compliance in the horizontal plane that I would consider an issue.
So, if I understand correctly, it is the hardened steel ballpoint standing against the teflon base that the magnetic bearing is to replace.
The shaft rotates into the steel sleeve (which if I understand correctly has the shaft rotate and scrub against the sleeve slot).
Now, do you really mean that this is more silent than a ball bearing?
PS. Actually, and after consulting wikipedia, the bearing I was having in mind appears to be a thrust bearing.
The shaft rotates into the steel sleeve (which if I understand correctly has the shaft rotate and scrub against the sleeve slot).
Now, do you really mean that this is more silent than a ball bearing?
PS. Actually, and after consulting wikipedia, the bearing I was having in mind appears to be a thrust bearing.
Ah yes indeed, a 'thrust bearing' and a ball-race bearing are the same thing (or perhaps you mean the one shown with rollers).
Sometimes the liners of a turntable bearing are phosphor bronze, often they are Teflon or similar - steel to steel is not used (that I am aware of). Not sure what you mean by the term 'sleeve slot', no slot exists as such.
Ball bearings are complex assemblies - for them to function successfully the balls must all be able to rotate and the two shells must also be able to rotate - all the independent parts rubbing and moving produces noise - the greater the load the greater the noise produced (this is well accepted in engineering).
"So, if I understand correctly, it is the hardened steel ballpoint standing against the Teflon base that the magnetic bearing is to replace."
Yes, that is exactly correct; note though that the steel ballpoint often bears down against an equally hard surface such as a hardened steel thrust pad or another ball bearing (steel or ceramic).
Sometimes the liners of a turntable bearing are phosphor bronze, often they are Teflon or similar - steel to steel is not used (that I am aware of). Not sure what you mean by the term 'sleeve slot', no slot exists as such.
Ball bearings are complex assemblies - for them to function successfully the balls must all be able to rotate and the two shells must also be able to rotate - all the independent parts rubbing and moving produces noise - the greater the load the greater the noise produced (this is well accepted in engineering).
"So, if I understand correctly, it is the hardened steel ballpoint standing against the Teflon base that the magnetic bearing is to replace."
Yes, that is exactly correct; note though that the steel ballpoint often bears down against an equally hard surface such as a hardened steel thrust pad or another ball bearing (steel or ceramic).
Actually the two different variations of bearings I was refering to are:
The first one is the thrust bearing and the second is the "generic" ball race bearing.
I am not very familiar with the English terminology here as English isn't my native language, so I am using the terms picked off wiki.
As I understand it, the thrust bearing is better suited to handle axial loads than the ball race one, where axial loads should be considered an abuse. This one is better suited to hold an axis on precise rotation.
I really find it hard to understand how the bearing type of metal contact (rotating steel spheres on steel tracks) should produce more noise than steel (axis, spindle) scratching on the inside surface of the shaft.
The first one is the thrust bearing and the second is the "generic" ball race bearing.
I am not very familiar with the English terminology here as English isn't my native language, so I am using the terms picked off wiki.
As I understand it, the thrust bearing is better suited to handle axial loads than the ball race one, where axial loads should be considered an abuse. This one is better suited to hold an axis on precise rotation.
I really find it hard to understand how the bearing type of metal contact (rotating steel spheres on steel tracks) should produce more noise than steel (axis, spindle) scratching on the inside surface of the shaft.
SaSi, many thanks again for the clarification - I completely understand what you mean. I'm sorry to be pedantic and I realise you are having to translate - I just don't want to misunderstand or tell you the wrong thing - thanks again for your patience.
The two bearings you show are essentialy the same thing though, as you say, the first is better suited to taking axial load. Your understanding (and your description) of the two bearings is absolutely correct.
The two bearings you show are essentialy the same thing though, as you say, the first is better suited to taking axial load. Your understanding (and your description) of the two bearings is absolutely correct.
In the compound bearings shown, for them to rotate at all they must be 'play' between each 'race' and each ball. There has to be play in two axis, a small amount of play, but play none the less.
Each point of contact is a potential source of noise.
So if your bearing has ten balls + 2 races that is 20 points of contact. A typical turntable bearing has one point of contact at its tip, and a well lubricated vertical surface that can be thought of as only being in hydrodynamic contact, unless you have a junk bearing.
Typically the single point bearing will rotate with several orders of magnitude lower noise than the sealed thrust or axial load cartridge bearing, even the best ceramic cartridge bearings.
if you want a good starting point, buy a Rega or Linn bearing from ebay.
Each point of contact is a potential source of noise.
So if your bearing has ten balls + 2 races that is 20 points of contact. A typical turntable bearing has one point of contact at its tip, and a well lubricated vertical surface that can be thought of as only being in hydrodynamic contact, unless you have a junk bearing.
Typically the single point bearing will rotate with several orders of magnitude lower noise than the sealed thrust or axial load cartridge bearing, even the best ceramic cartridge bearings.
if you want a good starting point, buy a Rega or Linn bearing from ebay.
Clearaudio 78mm CMB magnetic bearing actual photos;
Two O ring magnet upper side, one magnet is down side.
Two O ring magnet upper side, one magnet is down side.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It's a form of ceramic - you can buy the same stuff from RS components (but it's not cheap); Rega use much the same material for the platter on their top models.
http://uk.rs-online.com/web/search/...sp=Merchandising-_-Featured-Product-_-1583095
I piece 15mmD X 100mm long is £49 !!!
I was/am considering making a sub-platter (in my design this would be the platter) from it but a suitable bit of stock would be £158.
http://uk.rs-online.com/web/search/...sp=Merchandising-_-Featured-Product-_-1583095
I piece 15mmD X 100mm long is £49 !!!
I was/am considering making a sub-platter (in my design this would be the platter) from it but a suitable bit of stock would be £158.
Hmm...I can't seem to edit my last post any further so here goes:
The Clearaudio design is only possible, with its small magnets, because of the relatively light weight of the acrylic platter that it supports (this is not a criticism just a statement of fact).
I am currently considering a design in which the magnetic field is actively compressed (rather than by gravity as in all existing designs). It is perhaps worth mentioning that my own research/experimentation is leading me towards extremely low mass/minimal record support, i.e. almost no platter at all,.
The Clearaudio design is only possible, with its small magnets, because of the relatively light weight of the acrylic platter that it supports (this is not a criticism just a statement of fact).
I am currently considering a design in which the magnetic field is actively compressed (rather than by gravity as in all existing designs). It is perhaps worth mentioning that my own research/experimentation is leading me towards extremely low mass/minimal record support, i.e. almost no platter at all,.
When I searched at McMaster, I searched for Macor. That being the brand you specified. I am truly impressed by that stuff. Machinable with standard tooling and all the pluses of ceramic. I love that the feeds and speeds are specified as well, so you don't have to learn by smashing all the tips off your tooling.
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