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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
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...
peterayer OP
1,382 posts
 
Thanks for everone's response. I bought another washer which is half the thickness of the SME washer and did some listening tests. With the new washer, the LP was essentially flat on the platter and tightening the clamp slightly did create good contact between the platter and LP.

For reasons I can't explain, the thicker SME washer produced slightly better sound than the new, thinner washer and also considerably better sound than with no washer or clamp. I heard a little more detail and darker backgrounds during very quiet passages of solo instruments and the overall sound was richer and fuller, especially with full orchestras. In a word, everything became slightly more three-dimensional. But the improvement was very subtle over the thinner washer.

Has anyone else had a similar experience?
nsgarch's avatar
nsgarch
2,524 posts
 
Peter, when I used my SOTA clamp, I kept about 3 different thickness washers handy and woud use the thinnest one I could to bring the outer edge of the record down to the platter (which you can never do 100% -- even 50% closure is enough to damp out resonances.

A medium mat (ie harder than felt) can help, just remember the washer still has to sit directly on the hard platter surface for the clamp to be effective. So you'll need to find a washer that's the thickness of the mat (cut a hole in the mat to acommodate it) and leave it as long as you're using the mat. Then stack an appropriate thickness washer on top of that depending on the flatness of the record.
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