Alternative platters ?

[Oldpinkman]

As an analogy for these curves we can think of a tool that magnifies dots on a tv screen and the brian blends them seamlessly into a picture.

Arthur

Who's Brian, and which blender does he use? - we're looking for a new one!

On a more important note I'm glad you haven't lost the faith - which means no excuses for not finding that premotec in a drawer for tomorrow

[MartinT]

It's a good plot, Arthur, and I assume the lack of circularity would be most likely down to a not quite perfectly machined pulley?

[FunkArt]

It's a good plot, Arthur, and I assume the lack of circularity would be most likely down to a not quite perfectly machined pulley?

Hello Martin,

I don't think so.
It makes more sense to us mere mortals to calibrate the graph to show a per platter revolution, as has been on the Techie.

Take a motor rotating at 250 rpm - the Philips AC motor, say. The motor rpm is fixed and so this would exhibit a 4.1 Hz modulation (250/60) for any pulley error i.e. because the platter rotates at .55 Hz, we would see some 7.3 wibbles on the great circle.
I use the above example only because in the case of the Bix, using a(ny) DC motor, one can vary both pulley diameter and the speed to get the correct platter rotation. Thus just from a picture we don't know what the actual pulley diameter / motor rpm is.
I'm going to have a guess at about 8mm = 1250 rpm, which gives us about 21Hz, which is pretty darn quick.
One wouldn't reference that for the great circle.

The flattening suggests a non-perfect rotation of the platter, especially as it is non-precessive. I.e. The flat is not wandering round the great circle but remaining in the same general area per revolution, which is well within either experimental tolerance or simply showing the engineering tolerance at play - Ouch. Sorry about that.

Arthur

[MartinT]

Ah yes, of course. There's me thinking direct drive. It has to be a platter or main bearing artefact.

[pure sound]

Isn't that plot from one of those BIX kit turntables with a Premotec DC motor?

(Oops, I see Arthur also pointed that out)

With regard to belt drives, fixed/suspended subchassis or belt drive with motor on subchassis, I'm currently enjoying Direct Drive on a suspended subchassis. Not a new idea by any means, Goldmund were doing it 30+ years ago but it seems to be a sensible approach and with no belt or pulley consistency to worry about!

[krugdoktor]

Maybe it got lost in all the 45 pages of this thread but I don't recall a single written word if Audio Al is happy with his (Mike) new platter!

[Ammonite Audio]

The flattening suggests a non-perfect rotation of the platter, especially as it is non-precessive. I.e. The flat is not wandering round the great circle but remaining in the same general area per revolution, which is well within either experimental tolerance or simply showing the engineering tolerance at play - Ouch. Sorry about that.

Arthur

I had a Bix and the platter was a very loose fit around the bearing sleeve (the platter actually wobbled), so Arthur's diagnosis fits perfectly with my obervations.

[Audio Al]

Maybe it got lost in all the 45 pages of this thread but I don't recall a single written word if Audio Al is happy with his (Mike) new platter!

Al has not fitted it yet
Will do at some point
Lots on at the moment with a club I am the treasurer of and it year end , Audit , AGM prep etc , And my job

How do I fit it all in ?

I do keep picking it up and going Ooo Arrr Etc

[Barry]

The best platters are made from an alloy of 25% osmium, 20% tungsten and 55% depleted-uranium. Accept no other - you know it makes sense!

[The Grand Wazoo]

That only adds up to 100% - real audiophiles demand products that are greater than the sum of their parts.