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LP Thickness/Taper

If anyone has ever wondered how LP thickness varies from lead in to runout, I just measured it.  It's well known that there's a taper to LPs, but I have never seen any actual data.

This is a 120 gram record.  The thinnest part near the beginning of the first track is 0.0415", and the thickest part at the very end of the last track is 0.0470" (+/-0.0005"). 

I know there are many ways to set azimuth, but most most people tend to do it optically with a mirror on the platter.  So, if you set your azimuth like this and are confident that you have it perfect, it will automatically be 0.12 degrees off due to the taper of the record.  I'm sure all records will have a slightly different taper, but I can't see it varying too much.

ketchup
wolfie62
352 posts
 

I always check azimuth in the middle of a thrift store record. And several 1/1000ths of an inch matters not! Not in the real world!!

baylinor's avatar
baylinor
1,400 posts
 

I always set all cart adjustments with it aligned exactly half way in the middle of the record. On my VPI Classic TT it specially matters for VTF and anti skate. But it would also be beneficial for azimuth if all records are built like the one you tested, which I doubt. Anyway, to test a cart alignment either at the beginning or at the end of a record makes no sense at all. Always test the middle for the best average adjustments. 

lewm
12,881 posts
 

Since the angle of incline appears to be constant from outer to inner grooves, seems to me if you set azimuth correctly at any point on the LP surface, there would be no problem related to a changing azimuth angle.

tvrgeek
299 posts
 

Another vote for the middle. 

mijostyn's avatar
mijostyn
8,517 posts
 

Every record is different depending on the flatness of the shellac master. What does it mean? Absolutely nothing. The geometry of the groove depends entirely on the orientation of the cutting head. It stays perfectly vertical regardless of the thickness of the record.

The tip of all styluses is radiused and does not have to be perfectly perpendicular to the groove. 30 seconds one way or the other is not a problem. Some  styluses like the Replicant 100 are more pointy (the radius is smaller) and are more exacting. 

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