Antiskating .... The last analog secret

Skating force is the product of the stylus' friction in the groove times the (imaginary) lever arm, whose length is the distance between two parallel lines: one, the L/R center-line of the cartridge and the other, a line parallel to that one but drawn through the main vertical axis of the tonearm's rotational main bearing. This lever arm distance remains the same no matter where on the record the stylus is; and unless the stylus' friction in the groove varies from outside to inside grooves, the skating force remains constant (although it's higher on loud passages due to more groove friction ;-)

If your tonearm has no headshell offset, nor an 'S' curved armtube, then no skating force will develop and you don't need any antiskating force. This is OK for 12" and longer tonearms which don't have much tracking error anyway.

The easiest way to check anti-skate (without an oscilloscope ;-) is to just look at the cantilever dead on as you lower the tonearm to the record. If just as the stylus goes into the groove, the cantilever shifts to the outside (relative to the cartridge body) you need more AS. If it shifts to the inside, you have too much. Note: (a.) This takes a little practice and a lot of light. (b.) It's easier to do with high compliance (MM) cartridges than with low compliance (MC) cartridges because squishier suspensions (MM) make the cantilever shifting easier to see. However after a little practice, it IS possible w/ MC cartridges. And anyway, this is to get you in the ballpark; final adjustments (no matter what method you use) will have to be made by ear. (Tip: try doing your listening tests with a mono record.)

Although the visual (+listening) method described above is as good as any I've tried, anti-skate adjustments render very subtle results. So it's exremely important that all other parameters be on the nose; including perfect azimuth, which is especially important when trying to find the correct AS force.
.

It may strike some of you as strange, but when I think of what takes place with (and without) antiskating force applied, and the benefits to playback (or lack of them ;-) my attention is not on the interaction of the stylus and groove, simply because the range of forces we're talking about w/ or w/o AS is minuscule.

It is my assertion that when someone perceives different playback qualities w/ or w/o AS, it's due not to the very slight differences in the stylus-groovewall pressure, but rather the accuracy with which the coils (or MM) are in alignment with the stationery parts of the cartridge: the magnetic pole pieces (MC) or the field coils (MM).

In the case of a MM cartridge, the magnet has a very small force field, and if it is being held slightly off-center by some skating force pushing sideways on the cantilever (see Thomas' picture;-), then its force field will not penetrate the coils equally.

Similarly, moving coil cartridges are designed with a little "English" on the suspension, so that at the optimum VTF, the coil/armature is at a perfect right angle to the (very powerful) magnetic force field created by the pole pieces. In fact if you search the vdH website, you'll find that A.J. himself recommends setting the VTF visually -- applying just enough VTF so that when the stylus is placed on the record, and the cartridge viewed from the front, the cantilever passes "right through the center" of the hole in the front pole piece! According to him, that's how you know the coils are lined up with the magnetic field and will produce the most output.

My point, is that different cartridges, due to their coil/magnet configuration, the strength of the magnets, the layout of the pole pieces, etc., may not all exhibit the same sensitivity to the slight misalignment resulting from a little skating force (or too much antiskating force!) And that it's not really about the stylus in the groove.

Doug also touched on an important point when he mentioned that correct AS will (these days) be much less than equal to the VTF! This is because that (old) standard was based on spherical and elliptical styli which develop much more friction in the groove than modern line contact or micro-ridge styli.

By the way, trying to set AS using a blank record surface is like testing your brakes on a frozen lake! If the stylus can't develop any friction (which it can't on a blank surface) then there will be NO skating force produced. Yes I KNOW, if you set the stylus on a blank record, the tonearm literally FLIES toward the label! But that's not due to skating force. In most cases, it's due to the twisting of the internal tonearm wiring -- something that causes even tangential arms to move across blank records! If you try and set AS using a blank track, you will be applying WAY too much AS!
.

Dazz, well you barely make it! Go to http://www.cartridgedb.com and go to their resonance calculator. Enter your FR tonearm name and model, the mass (use 48gm to account for cartridge weight and mounting hardware) and hit calculate. You'll see that at a compliance of 8 (for that cartridge) you're still in the 'preferred resonance' range at 8Hz.

What I find weird about the cart in Thomas' pic (is it a Lyra?) is that the cantilever appears to be permanently displaced. If the suspension is OK, and the cantilever HASN'T BEEN BENT! it seems to me it should return to the centerline or close to it. I think Kirk is likely correct about the thing getting whacked ;-)

Here's the deal on styli and friction: line contact (or micro ridge, etc) styli spread the tracking force of the tonearm over the entire length of their (line) contact with the groove (two lines actually) whereas a conical or elliptical stylus only contacts the record groove at two points. So even at the (relatively) light tracking force of MM cartridges (1 gm +/-) versus the much heavier VTF of MC cartridges (2+ gm) the actual pounds per square inch applied to the vinyl by a line contact stylus, even at 2+ gms VTF is far less than the psi of an elliptical stylus on the vinyl (to say nothing of the fact that the elliptical stylus doesn't fit the groove very well.)

With that in mind, it's easy to see why modern line contact styli don't produce much friction in the groove and so require much less (if any) AS force.

Although some modern MM cartridges use line contact styli, most are found on MC cartridges. The relatively stiff suspensions of MC cartridges are unlikely to deform sideways (enough to matter) from the little bit of skating force produced.

Or you can just go to a 12" transcription arm and forget the whole thing!
.

Nsgarch, I've always thought the line contact styli have a greater contact area than the elliptical ones. Greater contact area means more friction (although the pressure/area unit is less).

Dazz, sometimes Physics can be maddeningly counter-intuitive, can't it?! The amount of skating force produced is directly proportional to the friction developed between the stylus and the vinyl. Since the contact area of a conical/elliptical stylus is essentially zero, the VTF divided by zero = infinity. Therefore the skating force (in theory ;-) should also be infinity (which it isn't ;-) but the psi is still much higher than that of a line-contact stylus, which 'spreads' the VTF over a calculable area.

In addition to the contact-area-vs-friction issue is this point: assuming the SRA is properly set http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1140840022&openmine&Nsgarch&4&5&st0 a line-contact stylus will 'lock' into the groove for effortless (in theory ;-) tracing. Conical and elliptical styli kind of 'skip across the high points' of the groove modulations (I'm exaggerating for illustration ;-) which adds additional friction.

If you ever have a chance to watch an earlier model Shure MM cartridge (like a V-15 Type II) and see how much the cantilever deflects, even at one gram VTF, you'll understand where the AS = VTF standard came from.

.

Dazz, if this thread has any point to make at all, it's that there ARE parameters for setting AS -- no the sky is NOT the limit (in either direction;-)

In the case of your SPU-85, an elliptical stylus + high VTF (3.5 g) = lots of friction! The compliance of the suspension is 8x (medium) so I'd be inclined to say that you could BEGIN (in this rare instance) by using the old "AS = VTF" standard. And then slowly reduce the AS until you begin to get some high frequency fuzz as Doug just described. Where you wind up will have to be your decision, of course. Patience is mandatory (patience, and a little self-confidence ;-)

Bob, I know it can be hard to use the visual method with low compliance cartridges. The Dynavector 20X-H (like most MC cartridges) has a dynamic compliance of: 12 x 10-6cm/Dyne. Anything below 15x more or less, is considered low compliance (meaning stiff suspension) and so it's going to be hard to see the cantilever deflect. Strong light and practice can help, as can a cartridge with a body that makes it easy to see and reference the cantilever's position. What's even more exasperating with low compliance cartridges, is trying to tell when the cantilever doesn't move!

Most (I'd guess as high as 90%!) of MC cartridges (both high and low output) have the following three specifications in common:

VTF = 2.0 gms +/- 10%
Dynamic compliance 15 (+/-) X 10 (to the minus 6) cm/dyne
Micro-ridge or line-contact stylus

This means that their AS settings will all fall into a rather narrow range -- which I've found to be around 0.8 gm to 1.2 gm. When you think about those (small) numbers, it's not hard to understand why many folks hear no difference with/without AS! I have to admit, I don't, at least not MOST of the time! But once in awhile, I'll hear fuzziness in a not-necessarily-loud passage (remember, actual track-skipping is not an antiskating problem ;-) When this fuzziness occurs, I'm always curious whether it means I need more VTF?, more AS?, more of both?, or possibly "Sit down you fool, someone overdrove the cutting head!";-) The last option is usually the case; and it happens, I've found, on a rather high percentage of Direct to Disc recordings!

For what it's worth, I follow these two rules (and I've never been disappointed): First, I always run micro-ridge-stylus-equipped cartidges at their maximum recommended VTF. This will not hurt either the cartridge or the record. And it will NOT (interestingly) increase the necessary AS force because it won't increase groove friction appreciably! Second, I set the AS at 1gm. That might be 0.05 gm too high or too low, but so what!? As many have already said here, it's close to impossible to hear any difference between AS = 1 gm and AS = 0 gm either! So I set it and forget about it! My rationale for using a LITTLE BIT of AS rather than none at all, is simply that (as someone already pointed out) the laws of Physics demand it!
.

Yes, I do live in AZ (Tucson) however the temp/humidity may or may not affect the suspension material depending on what it is (hopefully the cartridge designer/maker chose a modern polymer) but temperature will definitely affect the magnitude of the skating force because it's a factor in the coefficient of friction (between the stylus and the vinyl.) I question though how much a summer/winter temperature difference would make because it would have to represent a small percentage of the heat generated at the contact point itself. The only place for the heat to go is into the vinyl itself and I have no idea how ambient temperature affects vinyl as a thermal conductor. However, I guess as long as it's cool enough to maintain its shape and not warp, it could absorb friction heat.

There are some vinyl connoisseurs who recommend an interval of "rest" for the vinyl before repeat plays. Personally, I never found myself wondering how long it might take for my grooves to 'cool down' (as I proceed to play the same track over and over again ;-)