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. |
lewm09-26-2017 3:00pm Cleeds,I understand record warps and the dynamic nature of VTF. That's exactly why I mentioned the differences between statically balanced and dynamically balanced pickup arms. 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.That's absurd, because a pickup arm would never be vertical. The truth is that static VTF - within any normal range of a pickup arm - is not influenced by the thickness of a record. Do you weigh more when you lie down or stand up? |
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. |
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. |
