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RE: Null points for 7" discs?

Posted by John Elison on July 5, 2017 at 18:26:48:
You might want to recheck your distortion figures. I get different numbers using a 230-mm effective length tonearm.

Remember, the modulated groove envelope is in-between groove radii of 53.975-mm and 84.1375-mm. With my null-points of 56.97-mm and 77.77-mm, I calculate the following:

Average RMS Distortion = 0.108%
Peak Distortion = 0.159%

With your null-points of 53.975-mm and 76.23-mm, I calculate:

Average RMS Distortion = 0.137%
Peak Distortion in-between null-points = 0.195%
Peak Distortion at outermost groove = 0.218%
Peak Distortion at innermost groove = 0%

It seems that your alignment produces higher levels of distortion everywhere within the modulated groove envelope except for the innermost groove where your inner null-point is coincident with the innermost groove.

Best regards,
John Elison