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Unipivot tone arms

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

lstringfellow
tablejockey
3,978 posts
 

On paper, unipivot is inferior.

Properly setup and handled, you're not going  to "hear" its  deficits comparing it with other implementations.

S.O.T.A. tables typically are NOT unipivot.

Longtime VPI user.

 

kennyc
1,713 posts
 

Got a used VPI that came with 2 unipivots, I upgraded the arms as I’m not a fan of unipivots.

larryi
4,169 posts
 

As I mentioned above, there are many kinds of unipivot tonearms, and different designs address performance challenges differently.  One cannot say that any particular design is superior or inferior because no arm does everything perfectly. 

Among the somewhat unique designs is the Supatrac tonearms that utilize both a fishing line and a sideways unipivot as the moving elements of the arm.  This is a unique design which I have heard, but, only in an unfamiliar system; the system did sound good to me.  

Viv Float utilizes a hardened ball sitting in a magnetic cup as a kind of unipivot.  Magnetic forces not only reduce the downward load of the ball on the cup, it is used to increase the resistance against movement of the bearing assembly within the cup thereby providing the needed rigidity of the bearing.  This arm has a lot of other unconventional design features that do away with most of the skating force on a cartridge at the expense of very high tracking angle error.  But, the end result is a very good sounding arm.  Again, it is hard to say how much the pivot design has to do with the sound, but, it sounds good so the pivot must be good.

The Kuzma 4-point arm is closer in design to a unipivot than conventional gimbal bearing arms.  It too is a very good tonearm.

I don't see any basis for saying that Graham, Basis, Kuzma, Supratrac, Viv Float, Moerch, VPI, arms are inherently inferior to other arms out there.  I don't think they are superior to other designs either.  There are many successful ways to skin this cat.

mulveling's avatar
mulveling
2,096 posts
 

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.

daveyf's avatar
daveyf
2,980 posts
 

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.

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