motor and circuit for diy turntable project

[SoundBound]

Hmmm, ok, thanks for that info Mark. So it would seem then that a turntable would naturally fight the centre point of spindle contact and depending on the spindle/bearing-sleeve construction/fit, the points where the spindle contacts the upper and lower lips or rims of the bearing sleeve could be of great influence to the quality of smoothness of rotation of the platter (due to the rotational nature of precession). So attention must be paid to the quality of bearing fit and/or any presence of play or wobble in the bearing system and not just to the quality of the spindle contact point?

Or am I messing this up?

[vdi_nenna]

In other words? The platter is worthless or not?

[Mark Kelly]

I think it's best to try to visualise the rotation and precession at the same time.
Look at the top in this link. It's spinning too fast for the video camera to show the spin but you can clearly see the precession - in this case it's because the axis of the top is slightly tilted so gravity is providing the tipping torque.

Now imagine your platter / spindle doing the same thing at about the same ratio of speeds. If you imagine how the spindle rubs against its housing, you should be able to see the contact patches on the housing rotating slowly in the same direction but 180 degrees apart.

If one of these contact patches is roughly in the plane of the side force from the belt / idler pully / whatever and another of them is placed some distance vertically from there and the tolerances are such that the degree of precessive motion is small (which requires that the bearing is stiff enough to resist the precessive force) it doesn't really matter where the vertical support is, it's not playing this game.

The point of all this is that there's more going on than the obvious.

[harwoodspark]

And it all goes out of the window when you place a record and drop the weight of an arm and cartridge on that well balanced platter....or does it?

[Mark Kelly]

If the system is designed to cope with precession, the source matters not one whit.

The tilting torque produced by stylus down force is variable but miniscule.

[SoundBound]

Mark, what bearing factors or design considerations would you think are paramount in dealing with precession? Would it be the tolerances of the spindle to bearing fit or would it be construction details of the bearing housing? I know that the Linn LP12 Cirkus upgrade kit includes a bearing housing with larger/stronger bearing mounting flange as an important part of the upgrade kit. And if I am not mistaken, the Linn spindle has some taper to it, from a web article:

I believe that the Linn bearing exhibits excellent performance because it is a highly specified, precision machined, set of parts that fit together with very close tolerance and run true. The fact that it also incorporates an expensive to produce tapered spindle likely plays a part in its ultimate performance, but how much of said bearing performance is actually due to that one feature?

(Link to Article)

Soundbound

[vdi_nenna]

Precession - Wikipedia, the free encyclopedia

[Stuartarm]

IMG_5683.JPG

Originally Posted by vdi_nenna

I got a quote from Choir Audio for a 2" platter polished and their bearing for $1300.

If you can use acrylic, 8audio.com has a platter for just over $200 with $80 shipping.
I bought an attenuator from them and the quality was good. Haven't purchased a platter, but strongely considering it.

BTW- the Choir Audio DIY parts are no more. They only make custom platters or you can buy their table.

what i got in from them for about same not including shipping...i designed the 2.5 inch platter and bearing assembly...polished pic available of platter and bearing on Choir Audio diy web sight http://www.choiraudio.com/IMG_5696.JPG

[vdi_nenna]

Here's a nice platter.

Classic Aluminum Platter Bearing [Table Parts:T-1014] - $800.00 : VPI Industries Inc.

[krandle37]

Hi Stuart, From where did you acquire the platter and bearing and what did it cost? From the pictures it looks like a substantial build.