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VPI 3D Dual Pivot Conversion Kit

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  • #91
    Originally posted by Brf View Post

    Stiction: I do not believe that the coefficient of static friction is an issue as the rotational torque generated by the lead in groove puts the dual pivot into motion prior to the stylus hitting a modulated music groove. I addition, the dual pivot is in constant motion throughout playback.


    .
    I have to disagree. The vast majority of records have off-centre holes which causes the arm / cartridge to swing back and forth with every rotation of the record. With each rotation, the natural inward swing of the arm must come to a stop, and then swing back towards the outer edge of the record, come to a stop again, and then swing back inwards....over and over 33 1/3 (or 45) times per minute. On some records this is obviously visible and on some it's happening on a much smaller scale, and may be invisible to the eye, but it's still happening. Static friction is certainly at play here.

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    • #92
      Originally posted by Waxxy View Post

      I have to disagree. The vast majority of records have off-centre holes which causes the arm / cartridge to swing back and forth with every rotation of the record. With each rotation, the natural inward swing of the arm must come to a stop, and then swing back towards the outer edge of the record, come to a stop again, and then swing back inwards....over and over 33 1/3 (or 45) times per minute. On some records this is obviously visible and on some it's happening on a much smaller scale, and may be invisible to the eye, but it's still happening. Static friction is certainly at play here.
      That’s a fair point as long as the non-concentric record hole causes a deceleration of the dual pivot that results in a change of direction. On some records, this can be obvious, on others, not so much… but none the less, a valid point.

      With respect to your previous question as to why the sphere diameter matters when spheres have a theoretical infinite contact. You answered your own question, material deflection under load.

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      • #93
        Originally posted by Brf View Post



        With respect to your previous question as to why the sphere diameter matters when spheres have a theoretical infinite contact. You answered your own question, material deflection under load.
        The sphere diameter doesn't matter. Any sphere will have a smaller contact point than a sharpened tip. Two theoretically perfect spheres touching each other will only be in contact on the atomic level. And obviously material deflection of a ruby ball will be much less than that of a stainless steel tip. The stainless plate will have deflection, but the ruby ball will still have a smaller contact point that the pointed steel tip. None of it matters because the device is flawed from the get-go....the eventual arc carved into the plate makes this obvious.

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        • #94
          The vpi conical tip is shaped to approximate a very small sphere. The ruby tip just has a larger circumference when compared to the SS VPI tip. Too me, the material difference, size etc is a moot point because I can't hear any difference between the various types.

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          • #95
            The origins behind this idea is not just about off-center holes. Stiction (static friction) or I also call it "striction" as in constricted movement is also a result of the compliance of the cartridge cantilever and the inertia/momentum of the tonearm effective moving mass.

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