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Zero Antiskate vs Stylus Wear

This article, based on a long term study, was “plagiarised” from another Forum. It’s quite an old article so apologies to “older heads” for whom this may be old news.
It comes from an era when light VTF = good, but was not necessarily true, however the basic principle of long term wear looks sound.
Styli were tested to destruction over their full lifecycle.

http://www.audiomods.co.uk/papers/kogen_skatingforce.PDF

Viewers may have to cut & paste but in the event of difficulty with the link I will give a brief summary :

Of 14 cartridge samples tested without bias, 9 of them suffered excessive wear on the inner groove. One was neutral and the remaining 4 were “outer wall”.
When bias compensation was applied to a group of 6 samples, the wear pattern that resulted was symmetrical.

Given the strong and logical argument that skating damages styli asymmetrically – and gives a skewed reading of the LP over time, the “deviations” are a concern i.e. why 4 of them behaved oppositely.
Poor bearings? Arm cable too stiff? Wrong geometry?

IMO most turntable enthusiasts considered it self evident that unilateral force would cause this type of wear pattern so we didn’t need to be told but documented study, even one as old as this, is always interesting.
The photograph of the spherical stylus is poorly resolved on this copy but it makes the point quite graphically.

Based on long term experience that the simplest things can affect the sound of a turntable, I cannot deny that the idea of “de-stressing” the cantilever by removing a poorly directed/located AS force IS attractive and may produce a degree of audible benefit…at first...(?!?!?!!!)
The doubter in me always asks the question : can a mechanical assembly successfully zero out all mechanical influence and give a pure result? (If true zero AS is the goal even arm damping might be prohibited?)

The principle of using excessive VTF (up to 50% more) to achieve the same “trackability”, without bias, it was suggested, merely accelerates the unilateral wear & tear with (presumably) commensurate damage to the LP(?)
The proposed compensation of up to ”50% extra VTF” sounded a bit excessive to me.
(I’d balk at applying more than 0.1g over maximum.)

Old as it is, I found this study mildly unsettling.
Comments and opinions are invited from both Zero-antiskate adherents and those who always use AS.
moonglum

Showing 5 responses by lewm

lewm
12,553 posts
 
Thanks for bringing that old study to our attention. I don't recall whether I ever read it the first time around. I could summarize my response with three statements:
(1) I don't know who ever promulgated the idea of increasing VTF to compensate for skating force without applying AS, but it's ridiculous on the face of it, since skating force will go up as VTF goes up (because friction of the stylus in the groove will also go up).
(2) We all know, and you guys have accurately restated, the pitfalls and inadequacies of the AS mechanisms on a typical tonearm, but the study would suggest that imperfect application of AS is better than no AS at all, unless one applies far too much AS, in which case one has created a new problem.
(3) So best compromise is to use AS but use it conservatively.

By the way, Raul, in passing you wrote something that suggested that headshell offset angle is a culprit in causing skating force, but even a straight tonearm with no headshell offset will generate skating force, so long as the cartridge is aligned with the stylus tip overhanging the spindle, because in that case the cartridge/cantilever is never tangent to the groove. (Not Newton in this case; Pythagorus is responsible.) The RS-A1 tonearm attempts to mitigate the problem by using UNDER-hang; the stylus tip is recommended to be about 20mm short of the spindle. (I am really testing this idea out, about the effect of overhang, but it seems correct to me.)
lewm
12,553 posts
 
Nick, But consider this: if a straight tonearm (no headshell offset) is set up such that there is any amount of overhang (meaning stylus tip overhangs the spindle, as is typical for all conventional tonearms), then the stylus can never be tangent to the groove walls, because, by the Pythagorean theorem, where the P2S distance is the hypotenuse of a right angle triangle, the condition a-squared (where a is the pivot to stylus tip distance) + b-squared (where b is the radial distance between the stylus tip and the spindle) can never = c-squared, the P2S distance, because a>c.

So now I posit that lack of tangency of the stylus to the groove walls will per se produce a skating force. This is NOT to say that offset angle cannot also cause skating force.

Picture a little red wagon where the front wheels are fixed in line with the rear wheels, but the long handle is free to pivot left to right. Now if you pull the wagon using its handle forward following any straight path that is parallel to but not directly in line with the direction determined by the four fixed wheels, you will generate a side force on the wagon. I think this is true.
lewm
12,553 posts
 
John, You are the first guy who has agreed with me on this. Last year, I decided to ignore the most common explanation for skating force (as related to headshell offset angle) and re-think it from scratch. What I posted above is what I came up with using the remnants of my understanding of Newtonian mechanics as taught to me at a very fine liberal arts college many decades ago. I purposely avoided reading other explanations. After having done the analysis in my head, I never did get around to adding in the effect of headshell offset angle. So I am in no position to argue one way or the other about the magnitude of the skating force that may or may not be generated by that mechanism; I thought it was quite possible that headshell offset angle would mitigate or exacerbate the effect of stylus overhang and most likely that the effect would be different at different points across the arc traced by the stylus. Thanks for the URL reference.
lewm
12,553 posts
 
Zen, Wait to you see a wheel. Now THAT's something amazing!
lewm
12,553 posts
 
To complete Raul's explanation, when the distance from the tonearm pivot to the stylus tip (P2T) exceeds the distance from the tonearm pivot to the center of the spindle (P2S), as is the recommended motif for nearly all pivoted tonearms, then you have "stylus overhang". When P2S exceeds P2T, then you have "underhang". I know of only one pivoted tonearm for which underhang is recommended, the RS Labs RS-A1.
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