SL1210 Platter 'wobble'

:scratch:
Hi all,
my 1210 platter appears to have what I can only describe as a wobble. Once on every rotation the tone arm visibly moves upward. The closer to the start of the record the more noticeable this is. At all other points of the rotation the arm is quite stable. I cannot hear any distortion though I would think that it is stressing the cartridge (Goldring 2400 ) quite a bit.

This effect is noticed on all LPs and I have checked that they are not bent. I have just installed the Mike New bearing but this problem was observed with the orginal stock bearing fitted also.

I have removed the platter to check the spindle hole and cannot say if it is perfectly round or not. This is the only thing I can think of that might cause this problem. I know that KAB say they will machine any platters that go to them and are found not to be true, so there does seem to be a possible problem with some platters.

Anyone care to comment or give advice on this?

Thanks,

Les

probably a stupid question... but is your mat flat.. i was using a roksan mat to start with on mine and it was hard to get it to sit flat for some reason - it did the exact thing you are discribing...

other wise you sound like a good candidate for dave/mikes new's new platter when its available

It obviously get worse on 45rpm! I've had this issue twice on two older decks with simular platters Rotel RT-3000 & Monitor Audio ET-500

Hi Les.

Assuming that the fit of the platter on the bearing spindle is as snug and play free as it is normally (i.e. no play whatsoever) The only possible explaination for what you have described is that the hole through the platter is somehow at a slight angle.

If the bearing shaft were somehow bent, that it would only do this on one of the bearings, not both the Mike New and the original.

Ignoring the arm for a moment, if you watch the top edge of the platter edge-on with no record or mat, can you still see the same movement? I ask because a 'mutant mat' would cause the same effect and would follow between bearing changes, assuming you've not changed mat recently.

Personally I'd have though a mutant mat was a lot more likely that aplatter that had somehow been drilled on the piss.

Quote:

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Originally Posted by hamish

probably a stupid question... but is your mat flat.. i was using a roksan mat to start with on mine and it was hard to get it to sit flat for some reason - it did the exact thing you are discribing...

other wise you sound like a good candidate for dave/mikes new's new platter when its available

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Given the vast number of platters produced and the usual level of precision they are made to (just look at the strobe 'knobbles'), as manky mat is FAR more likely AND much easier to fix.

Hi and thanks for the replies so far. The mat is new, got it from Dave C.

Yes, if I look at the platter with no disk (just the mat) it is still noticeable. This was also true with the standard mat.

I can only think that it is a problem with the platter.

The new platter which I understand is being developed (though I know no more about it than that!) is on my to buy list if I haven't spent all my money by the time it is available. I can say this now because I know that Dave C will only market a product that has genuine value.


Les

This might help http://www.youtube.com/watch?v=qLOjU...eature=channel

Looks like swapping the bearing out is a doddle too.

surly you are at an advantage being so geographicly close to dave, get him to have a look at it...
it should be quite easy to see if the whole thing is wonky or if it has a dent or warped edge? that would make identifying the problem easier...
which of these is it do you think?

http://i728.photobucket.com/albums/w...laterwonky.jpg

not that im gonna be able to help but someone else might if the problem is a bit clearer..

Quote:

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Originally Posted by Stratmangler

This might help http://www.youtube.com/watch?v=qLOjU...eature=channel

Looks like swapping the bearing out is a doddle too.

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Good vid....certainly gives confidence in being able to do the job yourself.

Castings do "drift" from initial machining, which is why Linn were supposed to "rest" LP12 platters after each major stage. When they needed stock and cut the resting times down, we had platters which "undulated" and went up and down way out of claimed spec. Linn replaced any severe ones.

Many of the old techies I have sold had "undulating" strobes at least, although I don't remember seeing many with severe up-n-down movement at platter edge. My SL-150 doesn't seem too bad, but some people are more sensitive to this.

Does the new platter sit on top of the old one, or is it a whole new assembly including magnet/rotor assembly? If the latter, I'd just wait for this I think, as you have the "New" bearing.