Are linear tracking arms better than pivoted arms?

02-22-10: Larryi

However, the pivot and fulcrum mechanical advantage means much less force is needed to move the arm around the pivot point as compared to dragging a very heavy (in the horizontal plain) linear tracking arm. Again, this is just the THEORY; whether this actually translates into a meaningful issue is another matter.

Exactly, I wonder if this is really significantly so in the real world?

Is there even a way to measure this lateral force/stress on the cantilever/motor assembly?

Anyone know someone who has a Fidelity Research FR 64s for sale?

Is there even a way to measure this lateral force/stress on the cantilever/motor assembly?

it would seem to be simple to place some sort of sensor between the linear arm housing (or the cartridge body) and press against it. the smallest force required to get the arm moving from rest would be the maximum amount of force required. it might be impossible to measure the force required on a pivoted arm since the arm is able to flex in multiple planes. how could you isolate the resistance in one plane?

since i removed the dampening fluid from my arm the lateral resistance of the arm has got to be negligable.

it's the stress of that initial starting force on the canteliver which potentially could cause premature cartridge failure. my experience is that a linear tracker with vaccuum is the least stressful environment for a cartridge since the record is always flat. my favorite Colibri (a fragile cartridge if ever there was one) lasted 5 years on the Rockport before i accidently broke the canteliver while dusting two years ago.

my linear tracking arm only has two issues; and that is to make sure that the lateral shaft that the arm housing slides on is perfectly level, and that the shaft is clean. cleaning is simply a matter of sliding the arm back and forth once prior to using. i check the level by tapping on the arm to unweight it at various places along the shaft to make sure it stays in place. if it drifts to one side i adjust the plinth leveling on the air suspension. it needs adjustment once or twice a year and takes 30 seconds.

Lewm, I built a servo for the Rabco (which uses contacts, not relays) so the contact had only to get below 1 Megohm and the motor would run. Then I put a large capacitor across the motor so it would ramp up slowly and turn off slowly. The result was that the motor was always on, and would set its speed according to the rate that the LP grooves dictated. This eliminated 95% of the hassle of that arm- it was reliable and quite precise as far as linear tracking was concerned.

Later I had an ET but after eating a few cantilevers, I ditched it. Obviously I had the wrong cartridges in it; you could sit can watch the cantilever move back and forth as the arm tried to negotiate the LP. If you have ever seen the arm 'wobble' you know what I am talking about.

There are cantilevers that are stiff enough so this effect is reduced. What is not known (IOW I have seen no measurements to this effect anywhere) is how much the cantilever actually moves to make the arm move. IOW if the cantilever flexes by only a few degrees (which will not be visible to the naked eye) than any advantage of straight tracking is lost to radial tracking where this does not occur (of course this phenomena could occur with a radial tracker too, but most cartridge designers are expecting a certain effective mass in the arm and so this should not be a problem).

Short arm tubes such as seen in the Souther have two issues. The first is that the arm bearings cannot be in the plane of the LP so tracking pressure will change as warps and bass frequencies are negotiated. The second is that warps will cause wow.

BTW to be clear about something: its impossible to have an air bearing that has no slop. If there was no slop, there would be no place for the air to be in the bearing. With precision machining and tight tolerances, the arm can be poised on its cushion of air, and not move too much- until it is disturbed by the motion of the cartridge. The fact is that the arm has to move back and forth and yet stay exactly on its locus. If it moves even slightly out of locus that will be interpreted by the cartridge as a coloration. Its a bit of a trick.

I'm pretty sure that everyone agrees that air pressure and holding tanks to promote stable pressure are important to the sound of the arm. If that is **not** the case, then I would agree that air bearings work... Right now I have a Triplanar, and I've had several pivoted arms before that, not because I think anyone of them are the state of the art, but because what I think is required in a straight tracker does not exist. I regard radial tracking arms as a temporary solution.

Atmosphere
"Short arm tubes such as seen in the Souther have two issues. The first is that the arm bearings cannot be in the plane of the LP so tracking pressure will change as warps and bass frequencies are negotiated. The second is that warps will cause wow."

My SOTA has vacuum disc clamping. Severely warped records will not suck down anyway, besides who plays warped records on a decent set up? So how much warp matters anyway? In the same vane, what sort of bass tracking are we talking about?
Wow is at a certain frequency range, or put another way, if I can't hear it, is it there?
regards,
Sam