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.

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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..

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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.

Why not take the platter off & lay it on a piece of glass top & bottom.

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Originally Posted by Andre

Why not take the platter off & lay it on a piece of glass top & bottom.

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Kind of what I was going to say. Glass is properly flat. Flip the platter over & see if it sits flat without any rocking.

Thanks everyone;

I still think it is the platter so I will try laying it on glass as suggested but I'm sure it's probably the spindle hole that's not quite right.

Isn't Dave C's new platter still 12 months away?

If I identify the problem I'll come back and let you know! :scratch:

Regards

Les

I think the plinth is a while away, but I thought the platter was iminent!
A good bit of kitchen worktop might be flat enough too

Thought it wasn't due until the end of the year, the platter that is. The plinth is still in the 'giving it a good coat of thinking' stage isn't it?

Hi Les,

http://img11.imageshack.us/img11/5822/picture064web.jpg

Here is a cross-section of the platter, not much to machine here if thats what KAB do.
The metal is only 2.5mm thick and the rubber 4.25mm
Does the taper part of the bearing protrude above the top of the paltter surface?
Get rid of any mats on the platter and then check the undulation.
It has been my observation in talking to many people about bearings and things, that the taper becomes stretched if the platter is continually removed, this maybe your problem

As you can see from the image, the cast aluminium thickness leaves a lot to be desired, compared with somthing nearly 1" thick!! on the shortly to be available new one.

The platter could be quite soon, I'm just waiting for Mike to send me a sample to do some measurements on.

Regards

Dave

How come we need to play around with mats to damp a "ringing" platter when the current model has rubber damping stuck to it underneath, which my SL150 doesn't have? Ok, ok, record support....

Hi Mike,

Could you resize that picture please? It's WAY WAY too big and knocking the whole page out of sync...

Cheers! :)

Marco.

you got a dirty sensor mike by the looks of things ... i recommend "visible dust Arctic butterfly" sensor cleaning products

Marco,
Sorry about that, I am using ImageShack and for a first time user, the resizing is not imediatley obvious.

Hi Mike,

No worries - I was the same when I first started posting pictures....

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As you can see from the image, the cast aluminium thickness leaves a lot to be desired, compared with somthing nearly 1" thick!! on the shortly to be available new one.

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Most interesting - what sonic benefits do you foresee will be brought about with the forthcoming (much thicker) platter upgrade and what, in your opinion, are the technical/engineering reasons behind its design? :)

Marco (an enthusiastic future customer).

Marco,
My objective is to produce a platter that really complements the potential of the direct drive system, and has far greater sonic qualities than the very inadequate standard offering.

I am machining the platters from quality aerospace aluminium, which in itself is not imune from ringing, however because the platter is machined from a solid blank It is expected that the resonant energy will be low. Also there are five brass inserts which are a shrink fit into the platter, these are designed to absorb and counteract resonance. There will be a groove machine under the main 300mm dia, of the platter for lifting purposes.

I have attempted to get some weight below the spindle support but this is controlled by the existing components on the circuit board which would appear to vary between models.
The new platter presumes the use of an external PS, the exisiting transformer and wiring will need to be removed and the top cover can no longer be used as it obstucts the lower part of the platter.
I guess this platter represents something of a radical departure from the norm. Dave will shortly be getting the first production unit for sonic evaluation using his test equipment.

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Originally Posted by Mike_New

Marco,
My objective is to produce a platter that really complements the potential of the direct drive system, and has far greater sonic qualities than the very inadequate standard offering.

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Mike, like Marco, I'm strongly interested, too.
But your platter will still fit the
1. Original bearing?
2. Timestep bearing'
3. Mike New bearing?

Thank you

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I am machining the platters from quality aerospace aluminium, which in itself is not imune from ringing, however because the platter is machined from a solid blank It is expected that the resonant energy will be low. Also there are five brass inserts which are a shrink fit into the platter, these are designed to absorb and counteract resonance.

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Sounds intriguing, Mike! I look forward to further developments with interest :)

Marco.

The proposed platter sounds well made (I'm sure it will be); but isn't the servo loop expecting to modulate a low mass/low inertia platter - not a high mass/high inertia element?

Do keep up - you'll need the bearing and Timestep mk2 first :)

Hi again,

thanks for all the interesting replies to my original post. I have looked at all the possibilities suggested here but am still at a loss as to the exact cause of what I am seeing.

As I have now decided to bring forward Dave C's 78 speed mod (assuming Dave is able to do it in the near future!) it might be as well for him to look at as someone suggested.

The new platter also looks to be closed at hand than I originally thought so that will be a definite upgrade.

Since my last post I have managed to trash my stylus so am waiting for AT440 from Dave which should be here in a couple of days. It's cheaper for me to try the AT rather than purchase a new stylus for my Goldring 2400!

Les

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Originally Posted by DSJR

Do keep up - you'll need the bearing and Timestep mk2 first :)

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Well indeed...but I don't see how either of those items address the issue I raised; if anything, the high drag of the bearing will be more likely to exacerbate the issue. The Timestep doesn't replace the servo system does it?

No, but the sub-standard (in Dave's view) regulator is bypassed with something far better, according to Dave's measurements posted on his site.. the servo behaviour (if that's what I'm seeing) is substantially improved under load..

Is it the behaviour of the servo that you are seeing? In what way is its behaviour improved?

mArk,
I have listened to other people talk about this in relation to other makes of TT
I have had the original new platter running on my test TT for some time now and have no problems. The motor drive on the SL1200 models, is essentially a three phase 12 pole coil system driving a 16 radial pole osotropic ferite magnet. The phasing is controlled by the eight-pole pulse gernerator which opperates on 3 coil pairs.

I have had no noticeable control problems, excepting that the big secret is the radial positioning of the pulse generator wrt the invisible! poles of the magnet. A clever piece of engineering by technis.

In fact the response can seemingly be tuned for maximum performance, by very careful adjustment of the pulse generator position. You can even make it go backwards quite happily!!!

The pulse generator is made by myself as they cannot be obtained separately, and preset onto the platter before testing and shipping.
The ferite magnet is simply swapped over to the new platter.

You will most certainly require my bearing, using any other would be a waste of money. The reason being is that is has a massive 8mm dia. Silicon Nitride ball as the support, running on a carbide pad in an oil bath.

but isn't the servo loop expecting to modulate a low mass/low inertia platter

Yes and no. I will need to check that when I get a prototype from Mike. It is adjustable anyway but what you don't get is the cogging that is measurable on most conventional AC and DC motors.

We may well refine still further the electronics at a later date. Not many after-market manufacturers can actually measure properly or at all using their own in house test gear. I can clearly see and measure the cogging of a certain belt drive turntable, this must subtly modulate the music being played.

With time an effort, the SL-1200 will morph into almost another entire identity, and that identity might well take on the rest of the World including £100K turntables?

Regards

Dave

Would Technics supply the raw motor assembly as an OEM product like they used to, or would they require orders of thousands to even consider it?

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With time an effort, the SL-1200 will morph into almost another entire identity, and that identity might well take on the rest of the World including £100K turntables?

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Oooh... I like the sound of that! :eyebrows:

:respect:

Marco.