VPI 3D tonearm

Hi Frogman.....Thanks for your evaluation of the 3D arm. I still have not received mine (4 weeks since I placed the order) . I am also perplexed why the same quality of sound should appear in all your recordings. It would seem that the arm, or something else would cast its resonance signature on all you're listening. If indeed the arm is not resonant, something else must be. When I get my arm, I will test its resonance.....according to Harry, it almost doesn't exist. We'll see. If your Koetsu is one of their stone bodied models....I do suppose you had the appropriate counterweight...?? The idea is to get it as close to the pivot as possible...200 grm counterweight? That one is not normally shipped with the arm. The arm comes with either Discovery or Valhalla...which one is yours, and did you give it a chance to work in.

Hi Stringreen,

The system that I heard the 3D arm in is not mine, but that of an acquaintance whose system I have heard many times. The arm cabling I believe is Discovery and it probably is not fully broken in yet; this could very well have been partly responsible for what I heard.The Koetsu is a wood bodied one. I may have overstated the issue of sameness
of sound but it was a perplexing observation. As I said, the sound was very fine, but I was comparing it to the Forsell table which is known for explosive dynamics. I would expect you will be very pleased with the arm. Keep us posted.

Stringreen, Why would you say categorically that the idea is to get the counter-wt as close as possible to the pivot? The square of its distance from the pivot affects effective mass. The stone-body Koetsu might benefit from a high effective mass. Most report that it does; for example it is said to perform wonderfully in the very heavy FR66S. Granted, for other reasons, a large pivot to counter-wt distance is not the optimal way to gain effective mass.

Lewn....When the counterweight is away from the pivot, and the arm/cartridge is negotiating a warp, the counterweight "wants to" continue in the direction it was thrown, thereby disturbing the tracking of the cartridge. When the counterweight is near the pivot point, it doesn't move as much and disturbs the cartridge much less.....letting it do its job as best as it can....making better music. The idea is to get the heaviest counterweight as close to the pivot as you can for best performance.

I can't speak to the VPI 3D arm, but regarding the counterweight issue, I agree with Stringreen. At least on my 12" SME arm, the counterweight is very heavy and is as close to the pivot as is possible with the design. My AirTight Supreme cartridge weighs 12.5 g which is the ideal weight for this arm and allows the heaviest SME counterweight to slide very close to the pivot. The cartridge was developed in part on this arm.

I believe the relevant issue is moment of inertia. The closer the counterweight is to the pivot, the less inertia and the quicker the arm can respond to movement as the stylus tracks the groove. And I presume the less the cantilever has to work to overcome the inertia of the arm, lessoning distortion as the stylus remains more in the center of the groove.

There is also the issue of resonance within the structure that supports the counterweight. If the counterweight is far from the pivot, I think the support is more likely to resonate, all else being equal.

This does not address the issue of resonance in the main armtube that was discussed up the thread, which is perhaps the main design goal of the 3D arm. It will be very interesting to see how this arm performs.