I was reading the VPI 3D Pivot Conversion Kit thread and – having never owned a VPI or other uni-pivot arm – imaging what the kit does and why it is desirable (or needed.) It came to me that I’m not well versed in tonearm topology – ignorant if you will – particularly about uni-pivots, but also about the issues surrounding topology choices and trade-offs.
My vague sense has the merit of the uni-pivot found in its reduced friction and lack of bearings and their attendant bearing resonance or chatter. I used to own an SME V and now a Tri-Planar and a Kuzma 4Point; those are the basis of my experience; the first two are built using bearings.
Questions 1: what does bearing resonance/chatter sound like? (I presume it is considered distortion and as with so many distortions it may best be detected by its absence.) Are there particular conditions where it may be caused or made more prevalent? Wider grooves, end of side, sympathetic resonance passed through the arm that hits the bearings’ resonance frequency? What should I listen for? Or is bearing resonance always there and you don’t hear it because, well, it’s always there?
Questions 2: is it possible totally to eliminate arm/cartridge/stylus roll in a uni-pivot? Not having owned a uni-pivot, when I think of one I think of the tight-rope walker carrying a very long staff that aids his balance. Some unis have out-rigger weights, some use magnetic force, some do what the the VPI 3D Pivot Conversion Kit does, Etc. – all aimed at keeping the cartridge/stylus upright(?) under conditions where the tight-rope walker’s wire is moving laterally. (yes, not a perfect analogy) Do most uni-pivots set azimuth by "leaning" the arm to one side? (Versus, say, rotating the arm via a worm drive a la Tri and 4P) Can the uni-pivot azimuth stay rock steady given its nature, that is standing or supported on a single point?
My language here is imprecise and reflects my lack of knowledge. Several of you know so much about how arms work and the design of different arms across the years. Hoping to learn something from these less-than-well-formed questions – then I can ask some more. :-)
My vague sense has the merit of the uni-pivot found in its reduced friction and lack of bearings and their attendant bearing resonance or chatter. I used to own an SME V and now a Tri-Planar and a Kuzma 4Point; those are the basis of my experience; the first two are built using bearings.
Questions 1: what does bearing resonance/chatter sound like? (I presume it is considered distortion and as with so many distortions it may best be detected by its absence.) Are there particular conditions where it may be caused or made more prevalent? Wider grooves, end of side, sympathetic resonance passed through the arm that hits the bearings’ resonance frequency? What should I listen for? Or is bearing resonance always there and you don’t hear it because, well, it’s always there?
Questions 2: is it possible totally to eliminate arm/cartridge/stylus roll in a uni-pivot? Not having owned a uni-pivot, when I think of one I think of the tight-rope walker carrying a very long staff that aids his balance. Some unis have out-rigger weights, some use magnetic force, some do what the the VPI 3D Pivot Conversion Kit does, Etc. – all aimed at keeping the cartridge/stylus upright(?) under conditions where the tight-rope walker’s wire is moving laterally. (yes, not a perfect analogy) Do most uni-pivots set azimuth by "leaning" the arm to one side? (Versus, say, rotating the arm via a worm drive a la Tri and 4P) Can the uni-pivot azimuth stay rock steady given its nature, that is standing or supported on a single point?
My language here is imprecise and reflects my lack of knowledge. Several of you know so much about how arms work and the design of different arms across the years. Hoping to learn something from these less-than-well-formed questions – then I can ask some more. :-)
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