Setting anti-skate

Coeffecient of friction is a number used to calculate the amount of force necessary to overcome the resistance of a standard material to sliding over a test material. (Times area of contact, downward force, etc, etc,)

The force (whether in pounds or grams) produced by a moving record groove "dragging" on a stylus is a result of the downforce on the stylus times the area of contact between the stylus and the groove times the sum of the coeffecients of friction of both the stylus surface and the convoluted (wiggly) groove wall surface.

Using a grooveless shiny vinyl record surface to determine antiskate requirements is utterly useless because:

1.) The surface of the blank vinyl has a coefficient of friction approaching zero,

2.) The surface of a polished diamond also has a coeffecient of friction approaching zero.

3.) The area of contact between the (bottom tippity tip of) the stylus and the blank vinyl surface is also nearly zero.

In this situation, and using normal VTF, almost no inward skating force can be developed because virtually no frictional force can be produced. SO, you ask, how come when I set my stylus on a blank record without any AS applied, it goes RACING toward the center?

Well, that's because most tonearms today are very sensitive, have a healthy inertial mass combined with almost frictionless bearings, and internal wiring that presents virtually no torsional resistance. Since the stylus is not CONSTRAINED in a groove, but sitting UNRESTRAINED on a flat polished surface, even a tiny amount of torsional force is going to "fling" that tonearm toward the center of the record!

In addition, if the record is not dead flat but the slightest bit concave (like from a record weight or clamp), and if the platter is not dead level, but sloping the slightest amount down, away from the tonearm side of the turntable, these factors only add to the phenomenon. In fact, I've watched a tonearm slide over a blank record without the platter even turning!

So don't be fooled. The object of antiskating compensation is to "zero out" the clockwise torsional (rotational) force developed by a cartridge/tonearm system in PLAY, in a REAL GROOVE that has a MEASURABLE coeffecient of friction.

Also, a word to those who intuit that quiet, high frequency groove modulations don't present as much (frictional) drag against the stylus as loud or low frequency grooves: you need to re-think that notion using real physics. The (observational) fact is simply that those loud, low frequency grooves, although having a larger side-to-side displacement than quiet high frequency grooves, have their undulations stretched out over a much longer (groove travel) distance, and do not present significantly more friction to the stylus than the (tightly etched) surface of a high frequency groove. The reason that, back in the day, loud passages got worn out faster than the rest of the record, was due to the poor tracking of the very low compliance (bordering on NO compliance!) cartridges of the time. And to make matters worse, often installed in the very lightweight tonearms of record changers!

Note: proper antiskating force, as Warjarret points out, contributes only a small amount towards the actual "trackability" of a given cartridge/tonearm combo. More important to that part of performance is the VTF (of course) and most important, the relationship between the compliance (springiness) of the suspension and the effective mass (i.e. natural resonance frequency) of the tonearm. In other words, a correct amount of antiskating compensation can help get the last drop of performance out of a good tracking arm/cartridge combo, but antiskating alone can not compensate for a mismatched arm/cartridge combo that simply won't track properly.
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Nsgarch, thank you for your detailed technical analysis, but your understanding of coefficient of friction is wrong in EXACTLY the way it brings you to the wrong conclusion. Your analysis utilizes your personal logic instead of an application of physics. So, all of your 3 numbered points fall apart from an incorrect primary assumption. Your problem is that friction is actually INDEPENDANT of contact area. If you don't believe me, look up the equation for friction on the internet: F=uN. frictional Force = coefficient of friction times Normal force. Nothing about contact area. Diamond touching vinyl has the same coefficient of friction whether touching by the "bottom tippity tip" or the entire playing surface of the groove. And, the normal force is determined only by VTF, again independant of contact area. 1) vinyl has no coeff by itself 2) diamond has no coeff by itself -- they have a coeff TOGETHER that is constant and (3) INDEPENDANT of contact area. The smaller contact area of a blank record just means the same force becomes a much higher psi (surface pressure). So there IS definitly a frictional force, it is close to the force in a groove, and it is adjustable by anti-skaing. THAT is why the arm will go racing towards the center unless an equal and opposite force in applied by the anti-skating feature. If you set a needle down on a stationary blank record it will NOT slide towards the middle. But it may slide towards the outside, because now the anti-skate is unopposed.

Warjarret, some of your assertions are correct. A coefficient of friction is indeed just a scalar number. It's used to calculate both static and moving (kinetic) frictional forces.

Kinetic coefficients are lower than static coefficients for the same material(s) and don't depend on the area of contact (once the two surfaces are moving.) And you are quite right that the frictional coefficient(s) between diamond/vinyl are constant. I should have said frictional force(s), my mistake.

In any case, the TOTAL force (or drag) exerted on the diamond is far more when it's sliding in a groove than when it's sliding across a smooth vinyl surface. Much of this increase is due I suppose to the tortuous interaction of the stylus with the groove -- a kind of mechanical (as opposed to frictional) resistance created by the diamond trying to get through that obastacle course, IN WHICH CASE you'd have to calulate a kind of EFFECTIVE coefficient of friction for stylus-in-groove.

Nevertheless, I'd be very interested in your explanation of why, at the same VTF, some cartridges require very little AS and some require much much more. According to your view of the matter, AS should be the same for all cartridges at the same VTF -- and I must admit, most tonearm makers think so too, but it just ain't so, as anyone who has played around with AS can attest -- and the reason why I prefer doing it visually first and then by ear. BTW, years ago, I used the blank vinyl method, and ALWAYS wound up with a far higher setting than recommended by either the arm or cartridge manufacturer or by my visual inspection --I don't know why THAT is but I quit doing it a long time ago. I suppose there are definative electonic ways of calibrating proper AS, but I never explored those.

Changing the subject, I saw a stylus/arm slide across a stationary platter (no AS applied) because the whole table was tilted slightly -- a good reason to make sure everything is perfectly level before attempting any adjustments. I level my table with the clamp and a record in place and the arm over (not touching) middle of the record. (Very important if the table is a suspended type.)

Nsgarch and I are getting closer to agreement now, because I agree that different stylus shapes require different anti-skating force, and that a blank record must also be different than a real groove. The interaction of the stylus with groove undulations definitely makes a difference in skating force, which agrees with other comments heard here that skating force varies with groove modulation. I just think a blank record is a good starting point, before fine tuning of the anti-skating. I think its about as accurate as trying to observe motion of the needle upon dropping it into a groove. Its a lot more difficult to see the needle move a little, than seeing an arm skaing across a smooth record! Plus keep in mind that many cueing devices don't exactly set the arm down straight AND many records have a little out-of-round wabble. These will give the stylus some sideways motion also. Furthermore, we need to figure out a final step which ACCURATLY provides the real adjustment. I think the only way to do this right, is by playing various test tones, and comparing right and left channel distortion on a distortion analyzer. Without this equipment, I agree that listening is the next best way.

Warjarret, as I said earlier, years ago I used the blank vinyl method, and I ALWAYS wound up with a far higher AS setting than recommended by either the arm or cartridge manufacturer, or by my visual inspection. It consistently yields AS values that are WAY overkill -- I'm not sure why that is (I quit doing it a long time ago) but it may simply be that the unconstrained diamond tip on a highly polished surface is too unstable a mechanical assembly, sucseptable to air currents, TA internal wiring, irregularities in the vinyl surface or whatever, but it always took two to three times the nominal AS force to keep the arm in place.
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