Unipivot vs Linear Tracking

Like Albert, I've been through a few arms too. I like the *idea* of LT, and have had a few. But- I found myself preferring a uni-pivot (the Graham) and ultimately the Triplanar over that.

I still want to see an LT happen though. My feeling is that the air-bearing approach is fundamentally flawed, as the lateral tracking mass is several times higher than the vertical tracking mass (which is about the same as a radial tracking arm). You need a *really* low compliance cartridge to make that work, otherwise you get tracking distortion as the cantilever sweeps back and forth.

In addition, the more pressure you put in the bearing the better it sounds. Here is a fundamental rule about LP playback:

There can be no bearing slop between the platter spindle and the cartridge cantilever. The coupling between these parts must be absolute! (BTW, any of you that ride motorcycles will recognize this rule, it is the same one that says there will be no slop between the handlebars and the rear wheel, if you want the bike to handle safely).

Air bearings break this rule, as a result, you can always get them to sound *better* but you can never get them to actually work completely right- and so they can be shown up by a radial tracking arm, which simply should not be.

There is a solution. There are motion devices that have zero slop in their bearings. Some are small enough to be used easily in a tone arm, solving the Rabco track issue. One problem that the old Rabcos had was excessive slop in the track and there was nothing you could do about it (in addition there were a host of other problems- I had one of these for years and solved some of them, but some were fundamental to the design and could not be solved).

The kind of arm I am talking about currently does not exist. But- if you used one of these tracks and installed a modern arm tube/bearing system on it, and then an updated electro-mechanical means of arm advancement along the lines that Rabco made, you could make something that would work really well. I've been thinking about this ever since I got rid of my Rabco 20+ years ago... :)

Until then I'm using a radial tracking arm and its awesome. It is so nice to put on a record and not fear any tracking issue, any dynamic range; just have the music emerge (and buy more records) :)

THK has a patented linear motion slide that is the perfect size for a linear tracker, has low sticktion and guaranteed no bearing slop. All one would have to do is put gimbled bearing and an arm tube, and...

I've stayed in the amp side of the business for a reason :)

I've had a THK slide sitting around for a while. Its low sticktion and lack of slop makes it an ideal candidate for a proper TL arm. Its also an ideal size.

Alun, the problem with many air bearing tonearms is that the lateral tracking mass is much greater than the relatively normal vertical tracking mass.

This causes the cantilever of many cartridges to 'walk' back and forth as it produces all the forces needed to move the excessive mass of the arm toward the center of the LP as it spins. The result is that often the tracking error caused by the cantilever bending is much more pronounced that that of a radial tracking arm. This can be reduced by using a cartridge that has less compliance but you run into troubles with the effective mass vs the mechanical arm resonance (which is usually between 7Hz - 12Hz for best results).

A linear tracking arm that relies on a servo to move the rear tone arm will have a much lower tracking error and no need for a low-compliance cartridge. The Rabco was one of the few arms to use a system like that, but otherwise was a terrible arm. The 1960s for the most part was not a good time for tone arm designs :)