VPI 2nd Pivot for 3D

@rauliruegas could you explain the problem you have with the video you posted and why this has any bearing to the merits of a unipivot design. As I see it the video shows the forces acting on a cartridge at needle drop, and speak more to a poorly damped lift/lower mechanism then anything else. Secondly the arm in the video is a gimballed design not a unipivot so the video has nothing to say about unipivot design. Anyway some more details on the issues you are trying to refer to would be helpful

Here's the link to the video in situ.
http://www.marklevinson.com/productdetail/~/product/no515.html

@moonglum may be correct as the video of the needle drop is of an Ortofon 2M Bronze (I think) whereas the 515 ships with (and is seen later in the video) with a Cadenza Bronze which looks quite different

all in all this is coming off like amateur hour by Mark Levinson and VPI

@rauliruegas is correct in pointing out that one of the challenges of designing a unipivot is addressing the question of lateral stability and providing for precise and repeatable antiskate. It is precisely these challenges that the designer of the brand of unipivots I prefer (Durand) addresses -- originally via the use of dual magnets to provide lateral stability and adjustment on the Talea and then through the introduction of a precision side bar (aka "2nd pivot") in the Telos and Kairos. The trick with the side bar is that it is engaged via an adjustable sliding weight so that you can set minimal contact force (or more if you so desire). Once this element is in place the rest of it, and frankly the cost, all is down to materials -- and yes the selection of materials in every place on the tonearm does matter. So I’m not surprised that the VPI with 3rd pivot sounds better but surely it would have made more sense to design this in from the outset?

By the way inspired by the video I also closely examined needle drops on both my arms (I have a Kairos for stereo and a Talea for mono) and both go straight down and land with no sign of any wobble 😉

@billstevenson Raul’s point is to look at 12s in where there is a needle drop with an Ortofon cartridge, the arm swings noticeably which Raul maintains shows the inherent instability in Uni-pivot designs (absent a pseudo second pivot like the one under discussion). Funny thing regarding this video is that the ML turntable is actually a gimbal design, the stupid art director for the video dropped in a shot of some other VPI turntable! This was all discussed earlier in the thread (see entries dated 7/26-7/27)

@stringreen it doesn’t matter what alignment you are using if you have mounted the arm at anything other than the P2S it was designed for you will not be able to align it (or not for all cartridges given possible play in the cartridge mounting slots). Desired accuracy for P2S is at least +/- 0.1mm and is easily achievable by anyone taking care in mounting an arm. It amazes me to hear a tonearm manufacturer tolerating tolerances this sloppy

To summarize @rauliruegas lengthy, incomprehensible and misspelled post

"I imagine myself as the cartridge tracking the record and I thereby know unipivots cannot work"

hmmm ...

@rauliruegas (respectfully) I have spent much time with gimballed (damped and undamped) and unipivot tonearms with a good variety of cartridges including some that are very demanding of the arm they are mounted on. All I can say is that in my experience I get better results (i.e more truth to the master tape, fewer distortions) with the pair of Durand’s I currently run. Of course you would argue that they are not actually unipivots as they have a second point of contact 😇

In comparison the last pair of traditional arms I ran (a TriPlanar VII and an SME IV) both failed to deal with the bass energy thrown off by my cartridges and distorted and became confused when stressed. This is not an issue I have ever had with my Durands (a Kairos and a Talea)

Now per cleeds experience the downside of unipivots is the constant worry that they are not quite on (the point that is) -- other than that they are completely stable and foolproof

Have you ever tried a Durand Raul? They might even convince you you still have something to learn ...

Sloppy language @geoffkait "geometry" typically refers to the alignment of the stylus relative to the preferred arc and (absent gross off center issues should not vary disc to disc ('tho the truly anal might switch chosen geometries depending on the disc they are playing and where they want to put the maximum distortion 😉))

what you describe would affect the VTF/SRA/VTA relationship which while an important part of cartridge setup is not usually thought of as geometry. Plus it's easily addressed via adjustment of whatever VTA mechanism you're using