Thank you all for an interesting, and informative discussion...
Please.......based upon the picture ...what was decided.
Should the facet 39 edge as shown in the picture be at 90 or 92 Degrees to the record surface for correct SRA of 92 degrees for a Replicant [A90]
all opinions are appreciated......
This question (90? 92? other?) is being actively discussed around the net over and over again. On some forums, there are threads and posts (some mine, that I will try to dig up) that basically claim the following: that SRA should be set such that Intermodulation Distortion is minimized, plain and simple, whatever the resulting SRA is. In fact, the Analogue Productions Test LP has a dedicated track to adjust based on that measurement, but you need specialized equipment. After a long ride with the A90, I settled at an elevated arm (at the rear) such that IMD is minimized by EAR, playing tens of LPs, while keeping VTF very close to the prescribed 2.3g. Tracking at 2.3g is exceptional, and I was convinced that Ortofon know they are talking about. Under the microscope, it kinda looks like the angle is around 91 degrees, but I haven't spent the time to measure accurately. What I can tell you, though, is that, as Ortofon claims, tracking at 2.3g and with the arm parallel, the stylus appears indeed 90 degrees - a great starting point, and testament to accuracy in their manufacturing.
Listening for IMD is hard, when the levels involved (up or down) are fundamentally small; but over time, you can get your ear to focus on certain unnatural sounds, which do improve with proper SRA adjustment, as long as other parameters (VTF, azimuth, overhang) are also adjusted at the same time - copious effort, but that's analog. I think it took me a year to get it optimized, maybe longer. Unlike others, what I don't do is adjust SRA for every record, and only because I don't care to have to readjust all other parameters.