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Folkfreak, I took a powerful magnet to the weigh pan of my digital VTF scale, and there was zero attraction of the magnet to the weigh pan or even to the body of the scale itself. Seems that even though your plastic-bodied scale and my metal-bodied scale look alike (maybe exactly alike), there actually was a good reason why mine cost more money, other than the metal outer shell. For once in my life, my extravagance paid off.
nrenter and brf, You both got it right for the wrong reasons. My physics professor in college would have given you both an "F", but he was mean. The force of gravity never changes. What changes is the magnitude of the force vector in the vertical direction, when you rotate the tonearm in a vertical arc away from or down towards the LP surface. The magnitude of the vertical force vector due to gravity changes because you are shifting the center of mass toward the pivot (if you raise the tonearm) or away from the pivot (if the arm wand moves toward the LP surface). It's like a seesaw. When you raise the tonearm, some of its mass is shifted toward the pivot and thus the pull of gravity on the cartridge is partly borne by the pivot, not the cantilever, during that moment.
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folkfreak, That's very interesting and a bit disconcerting. Steel can contain some low concentration of iron, so that may be the problem. I will check the weigh pan of my digital scale with an actual magnet, to see if the magnet "likes" the weigh pan at all. FWIW, the weigh pan on my digital scale is white-ish in color and looks like it may be ceramic, not metal at all, which I hope is the case.
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cleeds,
Let's agree to disagree, once you have acknowledged the following:
(1) Our disagreement is NOT about the degree of difference in VTF caused by a warp or whatever. I have written twice already that I agree the difference is "small" (if we're talking about LP thicknesses). I thought we were arguing over your statement in response to someone else, to the effect that VTF would not change AT ALL when the stylus traverses a warp, because (you said) gravity is a constant, etc. I of course agree that gravity is a constant, but you failed to take into account that raising the tonearm up above the horizontal, as happens when playing a warp, does change VTF, because it changes the geometry and introduces a force vector that is not directed downward, perpendicular to the LP surface. That small force vector subtracts from the effect of gravity to pull the cartridge down on the LP, reducing the effective VTF. And talk to Einstein or any other theoretical physicist, if you cannot abide thought experiments. Based on the limits you want to set on logical arguments, we would still believe in a flat earth.
I notice now that you have changed your tune; you now say that the "thickness of an LP" has a "trivial" effect on VTF. At least you agree that a thick vs thin LP or a warp would have SOME effect on VTF. And I am telling you why it would.
(2) The bit about Dynamic VTF. You are confusing me with someone else (whom I respect) who commented that tonearms with dynamic VTF would be less subject to variation in VTF on warped LPs. In fact, I think you're misquoting him, but go argue with that guy. |
Folfreak, The digital scale that jbny referenced has a non-magnetic weigh pan. Or at least it says so on the spec sheet to the right of the photo. Thus it should not be influenced by the magnet inside any cartridge, even the stronger magnets in MC cartridges. That same scale recommended by jbny has evidently been re-packaged to death, in both metal and plastic cases. I see it all over the place under different brand names, and in fact I own one with a metal case, for which I paid about $50. I check mine regularly with the reference weights, and it remains very accurate.
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You don't understand. And you don't want to understand. So why bother? Read a physics book with a chapter on Newtonian Mechanics.
Or simply do the experiment I suggested: Measure or set VTF with the tonearm parallel to the surface of an LP. Then place a couple of spacers under your digital scale so that the cartridge has to be raised by a cm or two in order to sit on the weigh pan, and the tonearm is now tilted "up" with respect to the pivot, and measure VTF again. The difference will be very small, but there will be a difference. (Which is why I suggest using a digital scale; you'd never detect it with a Shure stylus gauge.) Don't come back at me until you've done this. If your tonearm bearings are excessively high in friction, it could obscure or enhance the results.
You don't seem to get that the thought experiment is valid; if the tonearm is completely vertical, VTF is zero, which means that as the stylus traverses the vertical arc of the tonearm between horizontal and vertical, VTF is gradually decreasing.
By the way, I never said that the thickness of an LP would make a big difference. The question was does it make ANY difference. It makes a small difference. Warps can transiently make a bigger difference.
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Cleeds,
Imagine that you are the stylus tip. With the arm wand parallel to the LP surface, someone has set VTF for 1.5gm. Now imagine that you encounter a record warp that lifts you up in the air by a few mm during each revolution of the LP. Since you are subject to gravity, you come back down on the other side of the warp, but during the moment when the warp elevates you off the horizontal, the pull of gravity is still perpendicular to the plane of the LP surface. Yet the tonearm is fixed at its pivot, so your journey back to horizontal must travel in the vertical arc dictated by the tonearm; the stylus tip (you) cannot follow the true vertical. Therefore, some of the force of gravity in the vertical plane is momentarily bled off by a smaller force due to resistance supplied by the tonearm, a force vector generated because the tonearm does not let the cartridge fall back down vertically. Hence "net" VTF is momentarily reduced by a small fraction. Got it now?
If you don't believe me, and if you have an accurate digital gauge, check VTF when you have the cartridge in the plane of a typical LP and then again with the tonearm elevated by a cm or two above the horizontal. I think the difference might be detectable even in these two static situations.
Another way to think of it: Imagine that the tonearm has unlimited travel in the vertical plane. It could then point straight up at the ceiling. What would be the VTF in that case? Zero.
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Folkfreak, There are many digital scales on the market that feature non-magnetic weigh pans. You are quite correct that any scale with a ferrous weigh pan would give an inaccurate measure of VTF and might even result in damage to the cartridge suspension. However, as noted, this problem is easy to avoid.
cleeds, True, gravity is a constant for any particular location on earth, however, actual VTF will vary depending upon where the tonearm is located in its vertical arc. This happens when you play a warped LP, for example. Thus it is important to use a scale that allows VTF to be measured at least roughly in the same plane as that of the surface of a typical LP. There would be a tiny variation in VTF, depending upon thick or thin LPs, not enough to worry about in my opinion.
Chakster, Like Raul often says, Relax and enjoy the music. As many papers as there are on using a digital microscope to set SRA, it is nevertheless a skill that can only come from doing it regularly under the guidance of one of the very few experts in the field. I advise you to do it by ear. Azimuth is yet another can of worms. |
