Anyone try the replica B-60 Fidelity Research VTA?

N Andric, I think you are saying that the  VTF in the FR 64S is largely governed by the spring that applies the VTF Which is controlled by a rotary knob on the side of the tonearm. I don’t think that makes any difference. If you have adjusted VTF  with the arm wand level to the LP surface, and then you crank the B60 downward , there would be additional force over and above the adjusted VTF, distributed according to the new angle of the arm with respect to the surface of the LP. In words, there is always some additional gravitational force on the tonearm in addition to whatever you have cranked in using the spring. The spring doesn’t cancel gravity. Try it and see.

nandric

My ''theory'' was that the spring tension in the VTF adjuster by the FR-64 ''does not care'' at which level the tonearm is in relation to the VTF. So I started with parallel position , the scale on the (SP 10) platter at the level of the ordinary (170g) record. The VTF was exactly 2 g. Then I moved the arm up to about 2-3 mm and measured again the VTF which was as before 2 g. Then I moved the arm to its original (parallel position) and from there for  2-3 mm down  . I got again 2 g as result.

Those are the results I'd expect when a pickup arm adjusts VTF in that fashion. That's why it's called "dynamic" balancing as opposed to "static" balancing.

Nandric, One rule of thumb in laboratory science is never to let your results dissuade you from an otherwise attractive hypothesis. So, first of all, congratulations to you for having the patience to do the experiment. My first reaction would be that your experiment illustrates just how minute are the changes in VTF associated with changing arm height at the pivot by only 2-3mm; minute enough that your SFG doesn’t detect it. However, there is also the remote possibility that I was wrong; dynamic balance does eliminate or at least ameliorate the amount of change in VTF associated with small changes in VTA. I was wrong once before, in 1952, so I suppose it’s possible that I’m wrong again. Once every 66 years is still a good batting average.

But seriously, it depends upon how the dynamic balance apparatus works inside the FR64S. I’ve never seen a cut-away drawing. Nor have I taken one apart. You start by static balancing the tonearm and cartridge so the arm wand floats horizontally in air at the VTF setting = 0. Then you twist the knob to achieve the desired final VTF. In some way, the device creates a downforce equal in magnitude to the setting on the venier (or near equal). It would seem to me that the spring-loaded downforce would still be subject to changes in loading (meaning the shift in vector forces) at the business end of the tonearm (the stylus), when the vertical position of the pivot point goes up or down in relation to the stylus tip. But I am willing to admit, maybe not. If not, I’d like to understand why not. I’ve read all the propaganda about dynamic balance preserving VTF over warps, etc, and I’ve swallowed it whole, until now.

Aha!  I see how you guys might be correct.  The downforce is entirely supplied by the built-in mechanism.  Therefore, it is, over a certain part of the arc of the pivot point, independent of gravity (because the arm "thinks" it's balanced, end to end, like a seesaw).  It would be, so long as the artificial downforce, supplied presumably by springs, remains linear as the arm moves up and down due to LP warps and whatever else would perturb the tonearm.  At some point, as the arm wand moves down or up with respect to the pivot, I would not expect the force to remain constant, because the force of a spring is directly proportional to its compression or extension.  But for all practical purposes, I concede.