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RE: It wants a Stevenson alignment

The Jelco 750 is not using a Stevenson alignment - your calculations give a different offset angle and null points to the actual parameters given in Stevenson's paper and to the null points you get by fiddling the inner null to get close to the overhang and effective length parameters using the calculator in the VE. Jelco are optimising the alignment for all 3 record sizes - that's why it is referred to as a "Univeral" alignment. For a 7" Rmin is ~54mm. Stevenson is also defining a method to optimise for all 3 record sizes, but is also optimising the alignment to take into account that 7"s are typically played at 45rpm so by putting the inner null at 60.3mm the peak weighted distortion at 54mm (at 45rpm) is still similar to the peak weighted distortion between the nulls and the outer radius.
Try the simulation again with a Lofgren A alignment and Rmin=53.7 and Rmax 138.7 and you will get all parameters matching more closely to the design specifications.

Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

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