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In Reply to: RE: Thanks a lot, but still one question posted by John Elison on February 03, 2017 at 17:57:15
http://www.jelco-ichikawa.co.jp/products/tonearm.html
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Here is a graph of Jelco's tonearm alignment compared to a graph of the optimal alignment for playing modern 12" LPs. Knowledgeable tonearm manufacturers like SME and Graham use the Lofgren "A" alignment. Check the distortion numbers in the turquoise cells.
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I just realized something that might be important. When I measured the P2S distance, I took the Linn Basik arm out and measured the center of the spindle to the center of the drop in hole of the armboard. My turntable CJ Walker 55 is a four-point suspension table. I just noticed that when the arm sits on the board, the board will be pressed down a little, which seems to also have the effect of pulling the center of the drop in hole away a little from the spindle. So now I believe the mounting distance of this armboard is indeed 211 mm as it should be, instead of 208 mm. I think the Jelco 750 arm is heavier than Linn Basik, so when Jelco sits on the board, it would press the board down a bit further. Maybe will pull the pivot away from the spindle a tiny bit more?
That's exactly why I suggested you use a Linear Offset jig which is entirely arm spec and mounting position agnostic and will avoid the issues of determining distances precisely in order to use an arc protractor.
It will be highly unlikely you could get your measurements much finer than ±0.5mm unless you have access to precision instruments.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Well, that's why I suggested trying the arm and see if it works before going to the trouble of drilling a new armboard. Measure P2S once the Jelco arm is mounted, if that's possible. You'll need an accurate P2S to generate an accurate arc protractor.
Good luck,
John Elison
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