My buddy in Burlington VT told me what you guys are expecting today. Wind chill of -25 degrees. I don’t own a coat for that. I am vacationing, if you can call it a vacation when you are already retired, at our house on the island of Vieques off the coast of Puerto Rico. The daily high temperature is about 85 and the low temperature is about 72. The beaches are beautiful and mostly empty.
An underhung tonearm all of which have zero headshell offset will have zero antiskate when stylus/cantilever are tangent to the groove or perpendicular to the LP radius in Wally terms. As for the effect or lack thereof of headshell offset angle in an overhung tonearm, I just took Wally’s conclusion at face value, that the demonstration applies for a spherical stylus on a grooveless vinyl surface. For me, that is just another reason not to set anti-skate using a flat vinyl surface with no grooves.
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Agree, centripetal force, in the Newtonian sense, is not the issue. I am aware that the "real Wally" passed away a few years ago. I just figured "wally" was a reasonable way of indicating that I was responding to your post.
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Dear Wally, From your excellent videos (excellent in terms of clarity and presentation), I get that when the line from the pivot to the stylus is perpendicular to a line drawn on the radius of the LP, there will be no tracking force. That is exactly what happens at the single null point one can achieve with an underhung tonearm. I also get your evidence that headshell offset angle has nothing to do with the skating force, but that is shown for a spherical stylus on a groove-less LP. (By the way, where did you get what appears to be a Columbia 6-eye LP with no grooves?)
Have you repeated the experiments with either a non-spherical stylus or an LP with grooves, say a 1kHz steady signal? I realize that with grooves one would not so easily be able to visualize the skating force. As to the video in Russian, the set-up is cool but the dialog is unintelligible to me.
Where did I miss your definition of "Effective Moment Arm"? I haven’t a clue.
From the point of view of pure physics, I still don’t see why an overhung tonearm with an offset headshell, aligned according to any of the popular algorithms, would not exhibit a skating force at either of its two null points that is for that moment due only to headshell offset angle. Maybe you need grooves and/or a non-spherical stylus tip to show that. I do agree with you that a lot of so-called authorities have run to far with that ball, saying that headshell offset is THE cause of skating, which I agree it is not.
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Timeltel, it’s great to hear from you. Hope you’ll stay around.
what with all it’s problems, drawbacks, and impractical aspects, it’s a wonder how good vinyl can be.
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I think we’re talking past each other. But I’ll take a look at your attachment.
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Dear Mijo, I never said the skating force was not affected by groove modulation. In fact, I agreed that it IS affected by groove modulation, which I described as “tortuosity”. My objection was to your repeated insistence that velocity or speed affects the friction force. It does not. Not because I say so, but because the equation for friction force says so. Thus we have to find another mechanism for the effect of groove modulation on the skating force that does work with accepted theory. I described two possibilities: (1) groove tortuosity causes momentary acceleration of the cartridge moving mass that also pulls the arm inward, adding to the skating force, and (2) Groove tortuosity causes mistracking. Mistracking causes momentary variation in VTF. VTF does affect friction and the skating force.
Wally, It is my impression that underhung tonearms elicit a skating force in BOTH directions. The force changes direction (where by "direction" I mean toward the spindle vs away from the spindle) at the single null point, where for one magical moment, there is zero skating force. So if you made a graph of the the skating force across the surface of an LP, for an underhung tonearm, you would get a straight line, give or take, that starts on the positive side of the X-axis, passes through zero at the X-axis, representing the null point, and ends up on the negative side of the X-axis.
Also, is it not the case that headshell offset angle does produce a skating force all by itself, at each of the two null points for an overhung tonearm, where the stylus is tangent to the groove but headshell offset still produces skating force?
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Mijostyn, I would take issue with a few of your points, but I will settle for this one as being the most egregious: "According to the equation the kinetic coefficient of friction changes with groove velocity"
Please show me that equation from a reputable source. As you are probably tired of reading, I have been saying over and over again that the friction force is independent of velocity, once the stylus is "moving". I only base this statement on every single physics reference I can find. So I need to see a reference to refute the notion. For all objects at rest, there is a quantity some call "stiction" or static friction, which is a way of saying that you need to put in a bit more energy than just enough to overcome friction, in order to get a body moving from rest. But otherwise, all is "kinetic". So there is no need to stipulate "kinetic".
On a separate note, I agree with MC that overhang does have a lot to do with the skating force, as it, combined with headshell offset angle, results in a constantly changing net Tracking Angle Error across the surface of the LP. Without the constant variation tracking angle error contributed by overhang, total TAE would be a constant, because the headshell offset angle is constant. Therefore, the skating force would be a constant, excepting the effect of groove tortuosity. Even at the putative two null points that can be achieved with an overhung tonearm with headshell offset, there is still some skating force. THAT skating force IS due only to the headshell offset angle, for those two instances in time. Underhung tonearms (which never are built with headshell offset angle, in my experience) do give zero skating force at the single null point available with such a tonearm, thanks to the absence of headshell offset angle. At the null point, underhung tonearms behave just like a SL tracker.
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"No overhang, no skating force." Wrong. Underhung tonearms produce a skating force except for the one instant that the cantilever is tangent to the groove (the single null point that one can achieve with an underhung tonearm). Haven’t we been through this before? All pivoted tonearms produce a skating force. So if simplicity of the explanation of skating force is your goal (as simplicity is usually your goal), and if you don’t like "friction", then you can say "no pivot, no skating force".
Also, for the Nth +2 time, speed of rotation per se is not a factor, once the LP is spinning. If it were, wouldn't skating force get much worse when you play a 45 rpm LP vs 33 rpm LP? And wouldn't the skating force be much worse at the outer grooves of any LP vs the inner grooves? Please read my post a few posts up from here. I could be wrong about how groove tortuosity adds and subtracts from the net skating force, and I would be happy if you can point out where and why. Some things actually are complex and resist attempts to simplify.
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Sure. Nowhere did I or anyone else say that groove tortuousity is the sole cause of the skating force. In fact, I think it's a minor factor causing minor ups and downs of the baseline skating force, which is due to friction of the stylus in a vinyl groove.
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No. Not to mention the fact that the skating force pulls the stylus toward the spindle. I agree that groove tortuousity does affect the skating force but not because it affects the magnitude of the friction force. Because.... for the Nth +1 time, friction is not a function of velocity. You can’t bend the rules of the basic science to explain the observation; you have to find another cause that does fit the science.
I am not at all sure I am correct, but my best explanation is that in tracing the tortuous groove, the stylus is pulled along at a "speed" dependent upon the platter speed and the distance of the styus from the spindle. The ins and outs of the groove walls however cause rapid instantaneous changes in stylus velocity, in order for it to negotiate the groove. Each instantaneous change, because it forces a change in velocity at the stylus tip, is an "acceleration". Acceleration is defined as a change in velocity, up or down. So now you have a mass (the moving mass of the cartridge) that is constantly accelerating. This would create or rather require the stylus to endure tiny forces according to Newton’s First Law of Motion (F = ma). It is those tiny Newtonian forces, which have a vector direction in the general direction of the friction force, that add to the net skating force.
I just thought of another possibility: The tortuosity of the groove causes the stylus to mistrack. Even when we don't hear it, there is mistracking to one degree or another. During a mistracking event, by definition the stylus loses or nearly loses contact with the vinyl, or the stylus may be driven against the vinyl. Either type of event would have a minute and transient effect on the instantaneous VTF, the force normal to the groove. That could indeed increase and decrease friction for fractions of a second. That could cause the ups and downs of the skating force, but not because of "velocity" or "speed" or whatever you want to name it. Mistracking can occur in the outer grooves, where velocity or speed is maximal or during the inner grooves, where velocity or speed is minimal, and is probably worse at the inner grooves.
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Mijo, for the Nth time, stylus velocity is not a factor in determining the magnitude of the skating force. Thus your statement, "listening for distortion and watching the cantilever displace as it hits the record are sort of arbitrary. To get a good cartridge to distort requires very high groove velocities that over estimate the AS force required.", contains an invalid suggestion that stylus velocity affects the skating force. Also, further up the thread you intimated that the coefficient of friction will vary across the surface of an LP. No it won't. For any formulation of "vinyl" used to manufacture a typical LP and the diamond stylus, the coefficent of friction is a constant. Otherwise, it would not be called "the coefficient of friction".
I apologize for the pedantry, but at least we can get the basic science right. Then we can disagree on everything else. Which is cool.
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In the above, I confusingly wrote, "So pre-supposing an effect of velocity on the skating force is invalid, if the angle in the equation for skating force is equal to the headshell offset angle." That’s wrong on the surface. I meant to emphasize that velocity is not a factor, regardless of angle. And as a separate matter, the equation quoted by Mijo is also invalid if it is dependent only upon headshell offset and not TAE.
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Mijostyn, There you go again! Velocity is NOT a factor in determining the friction force. Friction force is very simply equal to the net force vertical to the contact surfaces of two objects (VTF in this case) times the coefficient of friction, which is different for any two materials in contact. So pre-supposing an effect of velocity on the skating force is invalid, if the angle in the equation for skating force is equal to the headshell offset angle. If velocity was a factor, you would have to change AS significantly for 45 vs 33 rpm LPs. Not to mention that the outer groove velocity is so much greater than the inner groove velocity that "velocity" would dominate the problem of setting AS. In your last post, you say the angle IS the headshell offset angle, but then you go on to say, "The reference is to the arm’s pivot not the record". I am not sure what that means. Headshell offset angle is the angle by which the headshell is "bent" with respect to the arm tube, as I am sure you know. It’s a constant at all times. But tracking angle error (TAE) is constantly changing during the course of play. This aspect of TAE causes a constant shift in the direction of the friction force vector which alters the magnitude of the skating force. So I posited that the "angle" in your equation could be defined as TAE + headshell offset angle. At the null points, TAE is zero but headhell offset alone still causes some skating force.
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Use an amount that does not give you distortion in the R channel (too little) or in the L channel (too much) and does not result in a deviated cantilever after several hours of play. And then, forgeddaboudit.
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Luisma, Depends upon how the AS device on your particular tonearm is graduated. I have often wondered about this. For vintage Japanese tonearms and some modern ones that have magnetic antiskate devices, we typically see the dial marked in whole numbers: 1,2,3, etc. And the owners manual will often tell the user to set the AS device to a value equal to VTF. This gives some of us the impression that AS should equal VTF. But I wonder if in at least some cases, the manufacturer marks the dial as a guide only. In other words, for dial marking of "2", you get an amount of AS that the manufacturer thinks is correct for VTF =2g. But the AS may be much lower in gm of force than an actual 2g. So when you say you are setting at 1.6 for a VTF = 1.4g, I don't think it necessarily means you are using 1.6g of AS.
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That equation is bogus IF it defines “headshell angle”= headshell offset angle. In which case the skating force would be a constant which we know it is not. However, if headshell angle is defined as (tracking angle error + headshell offset angle), maybe it makes sense. Gotta think about it a little more but that seems to work.
I was interested in your response re how you use the scale. Dover explained your method, or as I understood his explanation of your method, as one in which you hold the scale vertically against the fingerlift on the headshell, with VTF set to zero and the arm floating. From your last post, I gather that is not the case. So what is your method, exactly? Did you try anything akin to my idea?
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My remaining question about Mijostyn's method is whether the typical Chinese-made digital VTF gauge is accurate when used in the vertical, rather than the horizontal orientation. I am trying to figure out how one would test for that. Or maybe Mijo tested for that. If so, how?
For the above reason, I have been conjuring a different method also using a digital VTF gauge that permits the scale to measure in the horizontal orientation. Place, say, a 5g weight on the scale. Place the scale with the weight on its pan to the left of the headshell or between the headshell and the spindle. Attach a thread to the 5g weight that pulls vertically on the weight and then goes over a pulley so the thread can travel in the horizontal direction and attach to the headshell. Now exert the AS force on the headshell. The reading on the scale should go downward from its baseline reading, e.g., "5g" will appear to lose weight. The difference between the no AS reading and the AS applied reading should equal the AS pull in g. Haven't yet figured out how to stabilize the headshell during this operation.
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Luisma, What is the method with the HFN test LP?
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Dover, no pun intended, I’m using two small nuts that each weigh ~1g, tucked as close to the crotch of the TP AS mechanism as possible, for the MMC1. The OEM AS weight weighs 5g.Thanks for the clear explanation of what Mijo probably does. I’ll give it a go.
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I was re-reading this thread, just because I have recently been wrestling with setting AS for a very low VTF, recommended 1.0g, for my B&O MMC1. Mounted on my Triplanar. To Mijostyn: I would like to measure AS by your method, but just from reading your description of the method in the OP, I am not sure how you did it. What does it mean to set the fingerlift "in the crosshairs"? My VTF gauge has no crosshairs; nor does it have any other sort of optical sights. Can you post some photos? Right now I am using two nuts from my tool stash, each weighing about 1g, tucked up as close as possible against the vertical arm of the AS mechanism on the TP. The weight that comes with the TP weighs 5g, and that seemed to be too much AS. (We are talking about AS weights mounted near the pivot; as Mijo rightly pointed out, what counts is the AS force at the stylus tip, which is near to the fingerlift on the headshell.)
Also, in November, 2020, Crustycoot wrote: "Isn’t the aim of anti-skate to prevent the mistracking that would occur if unequal groove-wall contact was applied during highly modulated passages? Isn’t this solvable by a small increase in downforce such that the “weak side” never fell below the trackability needed to negotiate the passage? That was the opinion of Edgar Vilchur of ARXA fame."
Vilchur may belong on any Mount Rushmore of historically important audio personages, but if he said what CC says he said, he was very wrong and probably trying to wiggle around why the tonearm on the ARXA has no antiskate adjustment. The root cause of the skating force is friction between the stylus tip and the groove. That force is most dependent upon VTF, given that in all cases the stylus is diamond and the groove is vinyl. (The materials determine the coefficient of friction which is also in the equation for friction.) The more VTF, the more friction, the greater the skating force. Any attempt to ameliorate the skating force effect by increasing VTF would only make the problem worse. So I hope no one out there took Crusty’s (or Vilchur’s) advice seriously.
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Nah! But MC, your avatar Einstein said something to the effect that one should first choose the simplest hypothesis to explain an observation, but not one that is “too simple”. We both agree that there is a skating force and that we need a little anti-skate. It would be too simple to ignore it. I just refuse to be bothered to measure it.
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Where does the 10% rule come from? I’ve heard it too, but I don’t know where or when. Let’s keep in mind also that there is no one value of AS that is correct at all times for all recordings. Ergo the analogy to aligning the suspension of an automobile is not compelling. Close is good enough and is likely to be exactly correct at certain moments.
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I partly agree with MC, in that there IS no "correct" amount of anti-skate, because the skating force is a constantly varying quantity, as the stylus traverses the LP. However, "some" amount of anti-skate is advisable, because all pivoted tonearms that are mounted such that the stylus overhangs the spindle will generate a skating force. So, if you ought to have some anti-skate, and since anti-skate cannot be adjusted during play, we all take a wild guess. Without knowing for sure, I would guess that the amount of anti-skate I use is about 10% of VTF, as Mijostyn so meticulously measured and applied. But what I do to determine the amount of AS is listen to the lead-in grooves with zero AS. This will usually generate some obvious R channel distortion. (The skating force is at or near maximum at the outermost and innermost grooves.) I then add AS little by little until the R channel settles in and sounds like the L channel. Then I light up a doobie. The idea that I would spend $250 for an AS gauge is laughable, not because I don't like expensive gadgets but because there is no such thing as "correct" AS, except, if your lucky, for brief moments across the surface of the LP.
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