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RE: Null points for 7" discs?

Posted by flood2 (A) on July 5, 2017 at 17:03:29

In Reply to: RE: Null points for 7" discs? posted by John Elison on July 5, 2017 at 06:53:41:

It is also noteworthy that 7" 45rpm discs are typically cut at higher amplitudes (with wide bandwidth) than the assumed 10cm/s peak that the weighted distortion figures assume and are cut much further in - I have many 7" EPs that are cut at 33rpm so the need to set the inner null slightly further in makes an enormous difference to the overall "uniformity" in replay quality as the effects of tip profile, cut and alignment (VTA/SRA mismatch) becomes increasingly significant with respect to the reducing groove velocity with radius. This can be achieved with a miniscule penalty in the increase in RMS distortion and peak distortion that is likely within the expected error in alignment.

The difference in RMS distortion between your LofgrenA solution with the compliant envelope and my nulls is 0.20% to 0.23% and the peak distortion is 0.10% vs 0.13%. In other words virtually no difference (considering people seem happy with 12" arms producing at least ~3x higher peak distortion on an LP using the IEC envelope!) since the ACTUAL distortion levels (taking into account all sources of distortion) typically encountered in normal playback are much higher depending on groove amplitude and typical HF distortion from the transducer of the order of 10%+ at 15kHz.

It is my belief that the normal alignment assuming equal peak weighted distortion across the modulated envelope doesn't sound as good compared to a gradually decreasing peak weighted distortion across the same envelope given the effect of compounding distortion as the groove velocity decreases.
Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

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