Unipivot tone arms


Help me Understand how Unipivot tonearms function  what are the advantages and disadvantages?

lstringfellow

When I was new to this, yes the wobbly unipivots (ala VPI) were unsettling. But this was misplaced nerves. Now - it’s no big deal! Use the cueing lever / lift. Of course, it doesn’t feel like a good idea to put a stiffly suspensioned, massy cartridge (Koetsu) on one of these. But for most MCs and MM it works fine.

There are many offshoots of the "pure" unipivot - usually by adding additional pivots of some sort (which is a broad canvas). I’d consider these more of a hybrid. The aforementioned Graham Phantom uses the magnetic stabilization, which works quite well and handles much like a traditional gimbal arm. Phantoms also do well with Koetsus, which seem to appreciate the enhanced stability.

VPIs can add the "dual pivot" mod. Though I’m not sure how well that "swash pad" bearing holds up over time. At least it’s easy enough to replace. I liked VPI’s metal unipivots - late builds of these wands were great, IMO. Really nice build quality and "feel". I had much more issues with the 3D and Fatboy wands. Very reactive to bass frequencies in my setup (~ 100Hz). I think it was more a matter of the wand material, than the unipivot bearing itself - but that could have played a factor too. I know the 3D / Fatboys are generally more popular than metal in this ecosystem - but not for me.

I wonder if the use of a unipivot has anything to do with cost of manufacture and complexity of same, vs the more expensive/complex gimbal. I use a variation on the unipivot design, a Well Tempered ’Black’ arm that sits the pivot via strings in a bed of silicone fluid. I do think that some of the unipivots have fundamental issues, like chattering on the point, or some other instability. The Naim Aro is a good example of this.

It might be cheaper/easier to build a unipivot, particularly because precision machining of the point and cup is not as critical as the machining of conventional gimbal bearings, but, some very good builders with very exacting machining make unipivot arms, and some very cheap arms are made with coventional bearings.  I don't think cost explains the choice made.  There are arms that do seem to be quite sloppy and chatter that are made with all sorts of designs. 

As to the Naim ARO, that is an interesting arm.  It may be a bit sloppy, and to my ears anyway "jangly" sounding, but I can see why some people like it for its lively character; I heard it perk up a system that sounded a bit too dark and dead sounding for my taste.

I had a Keith Monks Audio Lab (KMAL) and a JH Formula 4 arm from Australia. Both unipivots. Now I have a Mayware from England - the original that JH copied. They all sound excellent!

Some unipivot tonearms (VPI for example) are poorly designed because they are inherently unstable, thus the tracking force is in a constant state of fluctuation as the tonearm traverses the record. I suspect this is why VPI has been moving toward gimbal bearing arms in recent years.

Graham Engineering knows how to make a proper unipivot.