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SME record clamp causing convex playing surface

I have an SME Model 10 turntable. I recently noticed that by following the manual's recomended procedure for playing records, ie. placing the included washer under the record label, placing the LP on the platter and then screwing down the record clamp, the LP's surface becomes convex. The center of the LP is raised higher than its perimeter forcing the stylus to run uphill as the record plays. I confirmed this conditon with a bubble-level. I also presume this causes there to be a space between the underside of the LP and the platter surface, greatest in the center and decreasing until the vinyl meets the platter near the perimeter, which can't be good. Does this condition, presumably on all SME tables, cause problems with channel balance, pitch, record/stylus wear? It seems to me that the ideal playing surface would be completely flat. Has anyone else made this observation?
peterayer
stringreen's avatar
stringreen
6,483 posts
 
It seems to me that the record should be flat in the table in order for the resonances of the plastic to drain away, and not be allowed to affect the stylus...no?
sgs
22 posts
 
I also have a 20/2 that was purchased new and the same thing happens. Taking the cost of the table new into consideration, I never thought twice about it. Just assumed there was science going on I didn't understand.
nsgarch's avatar
nsgarch
2,524 posts
 
The famous SOTA reflex clamp comes with a washer and does the same thing. The idea is to force the outside edge of the record tight to the platter, even if it isn't perfectly flat. If your records are pretty flat anyway, just use a thinner washer; I wouldn't recommend 'no washer' because then you might end up raising the outside edge of the record and you don't want that.

Don't worry about the stylus travelling uphill. It won't even notice it, just reduce the anti-skate a little bit ;-) My Goldmund platter is slightly concave, and the result is about the same when the clamp is set.
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dopogue
1,773 posts
 
This is one of the reasons I gave up on clamps 5 years ago. Sounds better now, too, with a Boston Audio Mat I on the table and nothing on the spindle.
jfrech's avatar
jfrech
1,816 posts
 
Peterayer:

You're right. Page 12 of my manual say put the washer on. Clamp just enough...

So I did it. It does seem to tighten things up slightly. Lil more focus and dynamics than with out the washer.

I'll go to home depot and try a thinner washer for my 180-200 gram records. This washer might be better for thinner vinyl...

Sgs/nsgarch might be right...
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