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Old 19th December 2005, 08:19 AM   #1
Sella is offline Sella  Finland
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Default TT from Rega bearing and motor

I planning to build a turntable using same Premotec 9904 111 31813 synchronous motor and 18mm main bearing than in Rega P2/3/25. I also have schematics for Rega's circuit to achieve less vibration result with this motor (practically just caps which changes the phase to different coils of motor).

I am going to build simple non-suspended plinth with loose armboard. Plinth is build up with laminating aluminium and pvc. This construction should effectively stop vibrations between components.

Now a couple of questions:

1. What about the platter? I am thinking of pretty heavy dynamically ballanced alumium disk. How heavy platter original Rega bearings can handle? I have original Rega subplatter. Should I replace it with something more impressive? Would some other material work better?

2. The belt. What material? Can I diy it? One option is to buy a original Rega.

3. What you think of this project? Makes it any sense? Has anyone tried this kind approach before?

Thanks for your answers!

Regards,

Ilkka
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Old 19th December 2005, 12:56 PM   #2
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In general, most belt drive suspension turntables have the tonearm and platter tied together on one suspended plinth, so that if there are external vibrations that get in, the tonearm, cartridge and stylus wonít move too much relative to the platter, and introduce unwanted sounds. So just having the tonearm loose and isolated by itself is not a good idea, because the tonearm will move around too much relative to the platter. Although it looks like the tonearm is by itself on a narrow board, like on the Linn Sondek LP12, underneath there is a heavy metal plate, or some other material, joining the tonearm to the platter bearing base. Have a look at the manuals for the Linn Sondek at http://www.vinylengine.com and youíll see what they do. And of course, the other reason to have the tonearm base connected to the platter base, is so that you can set up the cartridge properly for minimum tracking error Ė if it is moveable, your tracking error will move, too!

1. I think the glass Rega platter on the P3 is pretty heavy Ė itís about half an inch thick, so you should be OK. But aluminium isnít the best material unless it has some sort of damping material attached to it, as it resonates too much. A solid thick aluminium platter would also be very heavy, so you may have to think about other bearings if you do that. Many are only solid around the edge, to provide impetus when moving. The original Rega sub-platter should be OK. The material for the platter is more important Ė you want an essentially non-resonant one, which is why acrylic, or glass, are often used.

2. Get a belt from one of the thousands of turntables out there Ė it doesnít really make sense to make your own. The Rega one would be fine.

3. Many of us have thought about making our own turntables Ė of course it makes sense. Rega are one of the better turntable manufacturers out there, so using components from one of their turntables, and using their circuits, is a good idea.
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Old 19th December 2005, 01:29 PM   #3
Sella is offline Sella  Finland
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Sorry, by "loose armboard" I ment changeable. My English is a bit rusty, since I haven't used it awhile.

I quickly calculated that the orignal Rega glass platter must weight around 2,5kg. How much I can go over this? Not much, I guess. Does anybody know how to calculate bearings?

The unwanted resonances of the platter is avoided with right kind of mat. Am I right? I believe that LP12 has an alumium platter also. What kinds of mats usually work with alumium platters?
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Old 19th December 2005, 02:03 PM   #4
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Aha, so thatís what you meant! Your English is very good, actually. Yes, that should be OK for the tonearm. Yes, the Linn Sondek, and many other turntables, use aluminium platters. The Linn Sondek was one of the better ones for resonance, actually. The aluminium platter on my Luxman turntable rings like a bell when you tap it. Itís true that a thick mat will damp it, but itís probably better to have it non-resonant. Some manufacturers actually bond things such as vinyl to the aluminium to damp it out. I have a Sansui turntable (XR-Q7) which was made in the mid 1980s which is like that, and it seems to be better than many other turntables having just an aluminium alloy platter. Rubber mats work quite well in damping platters, but thick felt is one of the better materials for turntable mats, which is why Rega and Linn both have used felt mats. The trouble with felt is that it absorbs dust, so you have to keep things nice and clean and vacuum felt mats regularly. While cleanliness is always good with records, they do tend to attract dust, even after antistatic treatments, and the dust then gets transferred to the mat. I still like other materials, such as glass or acrylic, as platter materials. If you donít introduce the problem (resonance) in the first place, you donít have to try and fix it.

I wouldnít expect that you could increase the weight too much Ė probably about 4 or 5 kg might be the limit, otherwise the bearing might start to break up if it goes outside its limit. There is also the possibility of increased friction, too, if itís too heavy, as well as increased loads on the belt starting it up, which could make the belt stretch and eventually fail. You could always increase the thickness of the belt, but that would transmit more vibration, youíd think, even though the Rega motors are fairly smooth. You have to think about a lot, designing turntables!
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Old 19th December 2005, 03:01 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by MosfetOwner
The Linn Sondek was one of the better ones for resonance, actually. The aluminium platter on my Luxman turntable rings like a bell when you tap it.
its remarkable how splitting the platter into a central hub and
outer ring ala Linn, Thorens, the original AR turntable and many
others almost completely kills the individual ringing of each piece
when they are mated together.

From my listening tests hard rubber is best - both for damping
platter ringing (glass in my case) - and damping of the record.

Personally think there is litlle to be gained going over 3kg mass.

You should also consider a semi-suspended design ala Roksan.

/sreten.
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Old 20th December 2005, 06:15 PM   #6
Sella is offline Sella  Finland
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Since I am going to use Rega's subplatter splitting platter to pieces is not possible.

I am thinking to go to with acrylic platter as MosfetOwner suggested. Hopefully my local machine shop is able to work with it.

Is there any other colored acrylic than transparent? Smoke grey or solid black would do the trick. Is painting out of the picture? Are there any other diy treatments? How about sandblasting? It would give nice effect, I think.
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Old 20th December 2005, 07:52 PM   #7
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Sella,

Something to keep in mind, I have heard it said that the Rega bearing is designed to work with a light weight plinth. This makes sense as the top of the range P9 has part of its plinth machined away to reduce weight and break up standing waves.

Paul.
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Old 20th December 2005, 08:22 PM   #8
Sella is offline Sella  Finland
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Yeah, that makes sense. What is light weight then? Isn't my composite pvc-alumium plinth light enough?

With my understanding of physics, this kind layered construction breakes the waves.
In general a wave passing from material to an other usually changes it's speed and phase also some of it is reflected back. Am I right?
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Old 20th December 2005, 08:54 PM   #9
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Quote:
Originally posted by Sella
Yeah, that makes sense. What is light weight then? Isn't my composite pvc-alumium plinth light enough?

With my understanding of physics, this kind layered construction breakes the waves.
In general a wave passing from material to an other usually changes it's speed and phase also some of it is reflected back. Am I right?
I would say your on the right line, just keep the mass down. For what its worth I was going along the same lines, see here
Cant tell you how it turned out as I have been busy with speakers as a blown tweeter left me with no sounds. I have modified the idea slightly to use a idler drive system, but still along the lightweight lines. ust trying to be differant, dont know if it will be any good!
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Old 20th December 2005, 10:04 PM   #10
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i have a planna 2 if you want me to weigh anything ect. Dont mind taking it apart either.
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