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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
lewm
13,740 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.
nick_sr
263 posts
 
Lew, what you describes makes sense but you must take directionality into consideration.

First off, we are describing a hypothetical tonearm, it must be straight, the cartridge must be in line with its axis and it must not have an overhang. As you stated if it has an overhang it will never have a null point. But let us assume that it has a null point at the groove which is tangent with the tone arm pivot point. At this one point there will be no skating force. Now take a standard arm at its null point, due to the offset angle it will have a skating force.

Now as this 0 offset arm travels away from the null point, in the spindle direction then the skating force should be pushing the arm in wards, however moving out wards towards the record's edge the skating force should be pushing the stylus out wards. So I agree, that there is a force, but it is not the same as the skating force caused by the offset angle and I would guess that it is much smaller in magnitude.
john_gordon
116 posts
 
Nick,
The forces you mention will be just the same in any arm, whether with straight or offset cartridge, as long as it has an overhang.

And similar overhang or underhang will produce similar skating forces, everything else being equal.

In your example, the arm has zero overhang at one point, which also coincides with it being a null, ie stylus and cantilever tangent to the groove.

As soon as an arm has any overhang there will be skating forces irrespective of whether there are nulls or not. Cartridge offset is a bit of a red herring.

See http://odysseytonearms.blogspot.co.uk/2011/10/antiskate.htmlfor more info on antiskate.
John
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lewm
13,740 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.
john_gordon
116 posts
 
Nick and Lewm,
I should have checked my post, as I meant to say that the arm in Nick's straight arm example "has zero skating forces at one point, which coincides with it being a null..." (not overhang)

The arm has underhang as measured from the turntable centre, and so experiences positive and negative skating forces, as the orientation of the arm varies as it pivots. There is just one point where both the arm and cantilever are tangent to the groove (as in a linear tracking arm) and so there is neither skating force nor tracking angle error. However, everywhere else the error becomes extreme and difficult to compensate for.

To reduce the error there has to be overhang, and as this is increased until, at two points (which will later be the nulls) the errors are equalised either side of a particular value.

The reason for cartridge offset is to minimise the error angle with regard to the stylus, and set the cantilever and stylus in line with the groove, thus constituting a null at two points, but this does not alter the angle between groove tangent, stylus and arm pivot which still varies across the record and is never zero.

And it is this angle which generates the skating force i.e. that between the groove tangent and the arm effective length, and only at the nulls is it the same as the value of the equalised tracking error angle and the cartridge offset angle.
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