Unipivot tone arms

dynacohum:

One of those Keith Monks mercury-dampened arms came with a vintage Thorens TD124 I bought. Scared the heck out of me, though I appreciated the inventiveness of the design.  I called the city and a guy came out in a hazmat suit with a specialized vacuum and sucked up all that Hg. They treated it as a spill, which, thank heavens, didn’t happen. Needless to say, I rebuilt the Thorens and added an Ortofon (Jelco) arm and a Cadenza mono cart. To play all those used mono’s I keep buying 🙄.  Happy listening!

@helomech First, you need to quantify the amount by which VTF varies over any vertical displacement (warp), say 5mm. That would be a seriously warped record.

Next you need to assess any impact that has on the cartridges tracking ability. And the map those, if any, to changes in SQ that can be attributed to those variations in tracking force, and not the warp itself. 

Finally, you need to assess any variation in VTF as a function of arm length, as well as changes in Stylus Rake Angle (SRA). 

Let's throw in one last variable, F=MA. To function at all, the stylus and associated motor, MC, MM, or MI, must move relative to the cartridge body and arm. Ideally the arm mass would be infinite, and the resistance to movement vertically or laterally should be zero. Obviously mutually exclusive requirements. Instead, we are left with a mass (the arm) suspended by a compliant spring (the cantilever, stylus, and it's suspension) that results in a resonant system that has been objectively determined to be optimal around 9-10Hz. This enables the relative motion and generation of the electrical signal, while not being excited by the lower warp frequencies. Get that too low and even a small warp can throw the stylus out of the groove. Too high and 'the tail wags the dog', the system is too stiff and the sylus/cantilever pushes the tonearm, wiping out the bass. A dancing bear, to be sure - the miracle being mechanical not that it dances well, but that it dances at all.

With that data, you can begin a conversation on this dynamic system. Until then, the model is incomplete, and the discussion theoretical at best.

My thinking is that Uni Pivot Arms addressed an issue with bearing manufacturing tolerances, materials, and quality control.  I think the bearing industry has caught up, and perhaps surpassed some of the Uni Pivot Arms out there (I have a couple of very vintage Mangepan arms, one installed on a vintage Realistic direct drive that has been converted to manual, from semi-auto. It is seldom used these past twenty years, newer equipment has taken over the dedicated mono role.)

Uni Pivots have a loyal following, and for that upper echelon TT and cartridge set-up, when set up properly, may remain unbeatable for awhile yet.

I have a VPI with a JMW 9 unipivot tonearm and a Koetsu Rosewood Signature mounted on it. It tracks and performs beautifully and I’ve never had any negative issues or concerns using it.

@dinov   I bought the original VPI Scout, same JMW 9 tonearm.  Unipivot works just fine.  I never liked the anti-skate feature using fishing line, feeling it had to be re-set too often.