SRA, why 92 degrees

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So, now I have (for the first time) a more extreme stylus profile I figured I ought to try and get SRA properly dialled in. Plus gave me an excuse for buying more bits for the camera, which is always good. So far have discovered that I need a better tripod and some new lighting for this stuff, but have at least got a roughly in focus shot of the stylus in the groove* and, looking at the reflection it's pretty close to 90 degrees. But the books say 92 degrees, but I've never found the origin for this to understand why. Also confused as the cutter head angle is reported to have changed over the decades..



I'm also rubbish at visualising grooves, but to me 90 degrees would seem to actually be right?


Anyone got a source that can help?


*Don't laugh at the shot. Still developing my technique here :)
 

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My 2p worth, having read and thought through this in the past and based on my measurements and setup listening tests:

Whatever SRA gives the lowest friction/drag coefficient returns the best overall results across a broad range of measures and listening tests. This seems to be overriding versus inevitable geometric distortion arising when playback VTA doesn't match recorded VTA.

Optimal SRA, and how sensitive a given cartridge might be to SRA, depends mostly on stylus profile and quality. It doesn't surprise me that non-90 deg is often the answer, nor that a small offset is the best general advice.

But I think this explanation is generally overlooked, and IMO is very probably real.

LD
 
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I need to try again with the macro lens tonight to work out where I am. I looked at the photo again and I have to get a better alignment to see where I am starting from. It's actually less than 90 degrees.



Noise measurements to infer friction will have to come later.
 
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I will fettle some more and report back. For now the 'new cart syndrome' is making it hard to be subjective as my old one was clearly a lot more worn than I thought and just enjoying records. I should be getting a half decent ADC in a week then I can start looking at noise.
 
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As regards getting a decent shot, I'll let you know when I succeed! A lot of people use USB microscopes but that hasn't worked for me as I have nowhere to put a laptop. So as I had a load of old prime lenses from my film photography days I'm currently experimenting with lens stacking, so have a 100mm lens with a 50mm put backwards on the end as the current test. So far has proved I need a better tripod and some new lights, but I'm close to a useable shot for alignment.
 
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This is a good question. If you read the link to Yosh you'll notice a whole load on VTA then the conclusion that you don't even know the VTA that the record was cut at so you might as well get SRA right.



Usually cartridges are made so at the spec VTA SRA is right, but mine is a Kustom job so there is a slight difference.
 
My take is

- there is an optimum vertical tracking force for each cartridge given their compliance and damping. Some specify tighter tolerances than others, and this is probably due to their manufacturing tolerances.
- optimum VTF should give a centered magnet and/or coil (along with an optimum antiskate force)
- if the optimum tracking force is set, you also should have the desired VTA and SRA

Now, the difficulty is to find the optimum VTF. Changing it will alter both motor centering, tracking ability, VTA and SRA.
 
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