Turntable "floating platter" attempts

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Hi folks!

I' have been playing around with this idea for a few days now and I want to start trying out prototypes this weekend.

If anyone has already attempted this, I would be grateful for any feedback.

I want to attempt a "floating platter". My first ideas were to literally float it in a high viscosity fluid and spin it via magnets in a sub-platter. But I quickly realized it would be slammed into the bottom of the container by the magnets.

Repelling magnetic bearings are too much hassle, and I saw the very complicated setup of the French TT that uses mag-lev.

I may have to settle for a simple elimination of the belt and go with a magnetic sub-platter the couples to the main platter. At least that way I will be able to eliminate any transfer of motor noise.

If anyone has an idea on how to float the platter in liquid, I would be intrested in trying it out.
 
Hi Manny and Pjotr
Back in the 70´s i made a floating platter tt by using a belt driven subplatter formed as a circular tub. Filled this with Citroen vegetable hydraulic oil and put a lightweight aluminium/cork floating platter inside. The upper platter had radial fins dipping down into the oil which made it follow the stream so to speak. I had a hard time keeping it centered to avoid wow. My aim was to eliminate feedback which worked, but compared to tt´s with a realy rigid coupling between platter bearing and arm bearing the floating tt was lousy at picking up small detail and dynamics. It was fun thou. Dont use a floting platter tt if Yové got a cat!
 
ingvar ahlberg said:
... but compared to tt´s with a realy rigid coupling between platter bearing and arm bearing the floating tt was lousy at picking up small detail and dynamics. It was fun thou. [/B]

Hi Ingvar,

That is one of my main concerns. I am thinking of a really heavy platter made of marmor or a sandwich of 10mm steel plates with damping material in between (easier to machine). The air bearing is just for supporting the weight, it will still have a centre pin for centring the whole platter. I have seen combinations of air bearings together with a vacuum "bearing" that were really “stiff”.

Cheers ;)
 
The air bearing idea has been covered exstensively in the turntable mega-thread (31 pages and going!)

There is a lot of great reading in there. Even the air bearing has that fatal centering pin which will connect the platter to the outside world, so to speak.

However, I have been going over this for some time, and I really can'y see a way to keep it simple and at the same time completely eliminate any connection of the platter to anything but fluid...SO! Here's what I am thinking to do.

Build a "platter assembly" that consists of the platter in an oil bath with either the centering pin or the "ring" rudder and centering pin. (you can find these in the mega thread).

THEN... make the sub-platter motor assembly and use magnets to turn the platter! I think this will work and since the platter is supported, eliminate the wow and flutter problems from wave motion without having a physical bond to the motor.... I can get to work now!
 
Hi all

I use a Well Tempered turntable and have been thinking about how
to use a heavy platter with the teflon-pad/silicon oil bearing of the Well Tempered.
Haven't red the turntable mega-thread, but probably will now.
Anyway, what if I use the teflon-pad bearing and support the platter with
an air bearing or magnetic ditto?

Just a thought, have to think more about this one :scratch:

cheers :drink:
 
Re. air-bearing and centering

Hi Manny and Pjotr

I remember a TT that was designed to float on mercury. I added an addition to the design that added a iol bath around the mercury bath to keep mercury fumes in. That design had a proposition to use a belt around the circumference, but with four bearings placed at equidistant points around the platter. If the belt is wound around the bearings it only touches the platter at four points around the circumference. That was designed to centre the platter without the use of a centre spindle. That leads me to my idea.

How about this for an idea:
1. use an air-bearing to float the platter, but don't use a centre spindle at all
2. put the platter in a 'well', with air-bearing nozzles similar to that used to float the platter around the circumference of the inside of the 'well'. That way air-bearing will not just be below the platter in order to float it, but also around it to keep it centered.

You can take this idea further and add vanes in the side of the platter, and then use the side nozzles to drive it.

For a brake you can use something similar to what Technics used in their SP10. They simply put a metal ribbon around the platter. The ribbon was fastened to the side and had a tightening mechanism. When the platter needed to be stopped, the mechanism contracted tightening around the platter. It is a very simple mechanism. In the idea above you don't have a centre spindle\bearing, so that can't be damaged by a system like this either :)

I hope my explanations are clear. I can see the idea clearly in my head, but trying put it in words is not so easy. ;) I will try to add an image (this is my first time) to try and explain the concept.

Ok, if the image loads, then you will see the platter in the 'well' with nozzles all around for the floating and centering. Please note that this is a very crude illustration, but it is only meant to try and better convey my idea.

Enjoy,
Deon
 

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diyAudio Senior Member
Joined 2002
Hi,

Deon,

The floating platter idea has a major drawback; the energy can't get away except through the stylus mechanism of the cartridge.

That is, unfortunately, the last point of exit for any energy you'd want.

It's also one of the reasons this idea was dirched, the other being the poisonous nature of mercury.

BTW, airbearing TTs suffer from the same energy drain problem.
The only viable solution I can put forward is to still use a bearing but with only a small load on it as opposed to the full weight of the more classic approaches.

Cheers,;)
 
Hi :)

The floating platter idea has a major drawback; the energy can't get away except through the stylus mechanism of the cartridge.
Can this not be addressed through the design of the platter? I mean, if you make a platter similar to the Teres ones (i.e. a few pockets in the platter filled with oil and bearings), will these not be able to absorb the energy and disappate it as heat? There may be another way to design the platter with internal components that eat the energy (as I wrote that I thought of the Duralube add that states that it 'eats the heat' :clown:) and disappates it as heat. The heat will easily be carried away as the air from the floatation passes over it.

Deon
 
diyAudio Senior Member
Joined 2002
Hi,

Can this not be addressed through the design of the platter? I mean, if you make a platter similar to the Teres ones (i.e. a few pockets in the platter filled with oil and bearings),

There are a few things you can do but this often compromises the mechanical integrity of the system.
One approach is the use of an acrylic to augment the perceived mass of the record, acrylic being very similar in impedance to vinyl.

The addition of lead, oil and or bearing balls is to damp the self-resonance of this mass and to increase the rotational momentum, not to drain energy.

Converting energy into heat is not a big issue, what you want it to do is to stay away as far as possible from the platter surface.
Therefore a single point of exit is needed, the best way to provide this a mass-loaded bearing tip.
The surface area is small and the pressure provides an easy pathway out yet a difficult path inwards.

The idea of the tiptoes and cones as used under equipment is a direct spin-off of this theory.

Cheers,;)
 
Fred,

What you are saying I disputed a while back, however after thinking it seems to make more sense. If the energy must be absorbed downward from the stylist it seems that the material of the turntable must denser at the bottom that at the platter to transfer this energy. If that is true would the bearing have to be larger and more surface area to transfer that energy.

:confused:
 
diyAudio Senior Member
Joined 2002
Hi,

What you are saying I disputed a while back, however after thinking it seems to make more sense.

I don't quite remember us discussing this but here goes:

Everytime the energy, envision it as soundwaves if you like, has to travel through a layer of different materials reflections can occur and we can't guarantee the mechanical stiffness of the bond between the two.

So the best way to go about this IMHO is to use a big chunk of the platter that's in touch with the record as an energy sink and choose this material carefully: it's properties have to be similar to the ones of vinyl.
The obvious material of choice is vinyl itself but it's rather hard to work with, not thermally stable and it scratches easily.

Enter the second best choice: acrylic, although slightly higher on the mechanical impedance scale the difference is neglegible.
It can be easily machined and rendered anti-static.

For the next step you can pick a material with a slightly lower impedance than acrylic. In that way any energy sunk in there will have a hard time crossing back again as it sees a higher impedance.
This works similar to a blocking diode and we used to refer to this method of construction as the application of a mechanical diode.

Cheers,;)
 
Frank,

Fred,

So your saying there is not need to try to dissipate that energy through base and then to the stand?

What I am using now is a SOTA turn table of course the it is hung from springs. Anyway, you had said that a sprung suspension was inferior to unsprung table. So if that so doesn’t still want to transfer that energy from the platter to the base and so on?

So if I want to improve my table don’t besides getting rid of the metal platter won’t the suspension hamper the performance even with some of Lexan or Delrin platter.
 
diyAudio Senior Member
Joined 2002
Hi,

So your saying there is not need to try to dissipate that energy through base and then to the stand?

You do but the first thing to achieve is to make sure it gets there as fast and unimpeded as possible and doesn't travel back up either.

So if I want to improve my table don’t besides getting rid of the metal platter won’t the suspension hamper the performance even with some of Lexan or Delrin platter.

As with anything else, compromises are sometimes a necessary evil.
Before you make any decision on upgrading it, one way to find out how the suspension adds it's own resonances to the system is to setup the TT in such a way that the springs are as stiff as possible all the while maintaining a level surface and an operable TT of course.

Once you're sure you have it set up this way put it either on a wall mounted shelf or a very heavy piece of furniture.

If you notice an increase in dynamic range while playing a record you can be certain that the suspension is muddling the sound when set to normal operation.

I'm not very familiar with the Sotas and other than their working principles I don't know all that much about them as they're not that common in Europe.

Cheers, ;)
 
Hi,

Hmm, lots of thoughts. But about what energy are we talking? IMHO it’s the energy that comes from the needle putting a force on the sides of the groove. Except for really low frequencies, that energy never reaches the centre spindle to be drained to the base I think. It goes right down into the platter and must be dissipated in the vinyl and the platter itself properly. But how many records are sufficiently well coupled across the entire surface to the platter to get this to work? With most of the records most of the energy is dissipated in the vinyl itself IMHO. A platter that rests on a magnetic bearing or air bearing is a mass-spring system. Its resonant frequency should just be far enough below audibility, say < 5 Hz. Such a system will have a pretty high Q, so problems may arise when external vibrations excite the system through the base. Maybe an oil filled magnetic bearing is a solution here? Or maybe an air bearing with an oil damping mechanism at the centre of the platter?

Cheers ;)
 
diyAudio Senior Member
Joined 2002
Hi,

But about what energy are we talking? IMHO it’s the energy that comes from the needle putting a force on the sides of the groove.

At least that's what I'm talking about.
The acoustic energy coming from the speakers isn't a direct concern when designing a TT. Or maybe I should say; shouldn't be.

Except for really low frequencies, that energy never reaches the centre spindle to be drained to the base I think.

The LF energy is mostly generated by cartridge/arm resonances and by the bearing assy. and shouldn't mix with the stylus-groove interface. Other than that energy, there's no LF to speak of present on a vinyl disc itself.
LF frequencies travel a lot slower the HF so whatever shows up is not going to the spindle but coming from it.
That is, of course, assuming the bearing assy. and spindle are machine out of monolithic piece of alloy or pressfit.
The avoid this interference it is best to separate the two as much as possible.
You wouldn't imagine the difference if you'd never heard it but it's not trivial.

Most of the energy generated by the stylus-groove interaction needs to be sunk into the platter and not allowed back in if that's possible at all.
To do this you use a material such as acrylic which allows for a tight coupling with the record and augments the mass of it allowing for a more substantial energy sink.

But how many records are sufficiently well coupled across the entire surface to the platter to get this to work?

This can be achieved with a properly designed record puck and platter surface.

Maybe an oil filled magnetic bearing is a solution here? Or maybe an air bearing with an oil damping mechanism at the centre of the platter?

In theory this, or something similar could be engineered but IMO it introduce other problems elsewhere.

Cheers,;)
 

rif

Member
Joined 2003
Paid Member
Hi all -- i'm no where near an expert, but Id' thought I throw in my 2 cents

1) Oil bath idea: I beleive some of the most accurate scientific tlescopes (the big ones on mountain tops, not the backyard ones) actually float on a sub-millimeter layer of pressurized oil. They need this so they can rotate through 360 degrees. This is just a guess, but I think that they would be much more sensitive to vibrations than our TTs -- a 10 micron amplitude vibration wave may or may not be audible, but I'm pretty sure it would smear a long duration image. (is 10 microns about the right size?)

2) No matter how it's mounted (magenetic, oil, traqditional) it all comes down to displacement right? Imagine vibrations as little pushes on the platter. If it's rigid, deflection at the bottom = at the top. If it's not rigid, then it acts like spring. Push a little at the bottom, it will push at the top, except not at the same instant (think of a slinky -- if you hold one end and dangle the other, then move your hand up and down).

So where's this going? Who knows -- I babble. But it seems like you either need dampening or dispersion to counteract the effect. By dispersion I mean that an input force at a point is spread over a large area at the output to minimize deflection if the platter isn't rgidly couled. Kinda like how bulletproff vests work.
 
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