A Different Drive System for Turntables

[The Grand Wazoo]

I wonder if anyone knows of any instances of the use of the linear induction motor in turntable drive systems?

A linear motor is one where the aim is to achieve motion in a straight line rather than rotation (you know the ones – like the Mag Lev trains use).

http://www.gaiawatts.novaewebs.com/i//MagLev.gif

I know we are looking for rotation in a turntable, but if you applied it to the platter rim, it would more closely approximate straight line motion. You'd either have to enclose coils within the rim or have a magnetised hoop attached to it.


http://www.productionmachining.com/uploadedImages/Publications/PM/Articles/Internal/0508_Aerotech_Linear_Motor_Cutaway.jpg

I'd think that linear motors might have several advantages in this application - there are no moving parts and so therefore there would be no friction or vibration. So, because acceleration is applied with an electromagnetic field, it should be quieter. Speed changes could be achieved electrically and you could also similarly apply braking if required.

The magnetic field would obviously have to be arranged in such a way as to minimise interference (in either direction) with a cartridge, but I don't think this would be insurmountable.

Any thoughts?



They're currently conducting research into linear motors as propulsion systems for space travel (initial launching) because fantastically high rates of acceleration can be achieved.

http://www.explainthatstuff.com/linearmotor.jpg




For info & basic explanation of linear motors:
http://www.productionmachining.com/articles/linear-motor-basics



Cheers

[chris@panteg]

That looks like it could be made to work

But and i am no engineer ' i would guess the development cost to be astronomical or would they ? and if so there is little point with the turntable market so small .

[Rare Bird]

Not so much that i idea, more a floating magnetic bearing.

J.C.Verdier are an obvious contender

http://www.jcverdier.com/RTC/cadre_menu.html

[The Grand Wazoo]

Yes. There was an idea like that, i was talking to Arthur K about this a few years ago.I think it was arthur.Was more a floating magnetic bearing

I was thinking motors rather than bearings, because the idea of opposing magnets with TT bearings is a little more obvious (I think Clearaudio use it). But yes, of course the advantage of using it for a motor might be that you could get a frictionless (or reduced friction)bearing for free.

[Mike]

Hmmm... I wonder what effect all these rather powerful (I assume) magnetic shenanigans would have on the delicate sensibilities of a poor old cartridge? :(

[pure sound]

B & O did it

http://www.beocentral.com/products/bg8000

[Mike]

Ah, the old "there's-nothing-new-under-the-sun" syndrome strikes again! ;)

[Kris]

The EAR turntable has a no-contact drive system as well. A belt drives the sub platter which then drives the platter via magnets. Not sure about the bearing though . . .

[The Grand Wazoo]

B & O did it

http://www.beocentral.com/products/bg8000

Ahaa! Interesting link that. Thank you.

....dammit, dammit, damnandbuggerit! - I thought the idea was too good to not have been implemented somewhere before!


It looks to me as though maybe the basic concept of the motor was wrapped up with a whole lot of other electronic gizmos. You'd have a job working out the good from the bad in among that lot, I'd think.

So what was wrong with it? Why didn't it take off?

[Rare Bird]

This was the best thing for me when it came out

http://www.vpiindustries.com/review_positive.htm

[Barry]

Nah! What you want is one of these:

http://www.thevintageknob.org/DENON/DP100M/DP100M.html

Just rip off that arm and fit an SME V.

Regards

[Barry]

Or, maybe one of these:

http://www.emt-profi.de/930.gif

An EMT 930st rim-drive (idler) turntable, powered by a 60W three-phase motor. I use one of these; speed is rock steady and rumble though not the lowest, is totally inaudable. The deck has that great 'drive' (no pun intended) and momentum, that is great for rock music and pretty dammed good for everything else.

Regards

[Beechwoods]

That B&O writeup makes me want to get one :)

[The Grand Wazoo]

It sounds like a bit of a triumph of gizmology doesn't it?

Except for this bit:


What is beyond doubt though is the poor quality of the materials used, the lid and lid hinge in particular were insubstantial (and frequently broke) and other parts were held in place by adhesive tape, not good practice in a machine of this class.

[Beechwoods]

:lol: Yes... and they're probably rare as hens teeth now as a result!

[DSJR]

The Beogram 8002 is the one to get, with either an MMC1 or MMC2, which can be rebuilt properly in Germany for well under £200. The Soundsmith B&O cartridges cost substantially more I think.. The 8002 had superior record support and sounded much better for it - like a very refined rega, rather than a techie blockbuster, if you see what I mean. They used a Tacho disc for speed stability and these can sometimes fail. I *think* someone makes replacements.

These decks don't go for huge money as I recall - well under £200 I believe.

My Dual 701 has a linear drive too I think......... Perhaps not, but the horizontal petal windings of the Papst EDS1000 motor supposedly minimised cogging from conventional Hall effect motors.....

[Barry]

All this sounds like a job for 'B&O man': Beobloke. :)

Regards

[The Grand Wazoo]

So other than the linked to B&O 8000, what others have there been with this drive system?

[Dave Hewitt]

Hi
I think one of the Strathearn jobs was linear drive
Dave.

[DSJR]

I think you're right. A tragedy that they were made with such flimsy and frail bits..

[chris@panteg]

Hi
I think one of the Strathearn jobs was linear drive
Dave.

I think they used to go backwards didn't they :eyebrows: ' made in N/ireland ' government backed project ? .

[The Grand Wazoo]

My Dad has a Systemdek that 50% of the time starts up in the wrong direction.

[DSJR]

Don't most Systemdeks use the standard 24 pole motor? If so, a fix should be easy ;)

[The Grand Wazoo]

Well, he uses it so infrequently that having to turn it off & on again about once every three years is no major hardship!