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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
peterayer OP
1,382 posts
 
This occurs with all of my records, any thickness. It is the original black SME washer that came with the table which I bought new from a dealer. I don't know the exact thickness or diameter of the washer, but I think it is just over an inch in diameter. I will measure it later. I do tap the edge, or check it visually, to make sure there is contact all around the perimeter of the LP and tighten it only enough to achieve this contact and no more.

Having thought more about this phenomenon, I think VTA is constantly changing because the tonearm angle is going up as the stylus is riding up hill slightly with each revolution as it travels toward the center of the LP. Perhaps I should contact SME or Sumiko.
jfrech's avatar
jfrech
1,816 posts
 
Hi I have a SME 20/2, I bought it new so I know I have the right washer. Mine does the same with the washer. I don't recall that it said to use the washer in most/all cases? I'll get my manual out...

I do notice subtle sound changes depending how tightly you clamp with out the washer. A dealer told me to tighten the clamp until the outer edges lift off the platter slightly then back off a little to get the best "clamp".

I have used the washer, but only for the reverse side of a badly dished record.
stringreen's avatar
stringreen
6,494 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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