Linear tracking - a myth debunked?

[Aristophanes]

One objective of tracking is reducing tangent error and liner tracking does this. But how much pressure on the outside groove wall does it take to move the cartridge. This is where pivot arms are better because they require very little force to keep the cartridge moving. You’ve got a 220mm fulcrum there on bearings. And the virtual pivot point is extended out another 150mm. I was able to reduce my tangent error down to around one degree by doing a bunch of things with overhang and null points. See


http://www.dvautier.com/nullpoint/null.htm

 

[vinylrayk]

Pivot arms suffer from skating, which is always changing, and causes a whole litany of distortion producing problems.

Ray K

 

[pfcs49]

One objective of tracking is reducing tangent error and liner tracking does this. But how much pressure on the outside groove wall does it take to move the cartridge. This is where pivot arms are better because they require very little force to keep the cartridge moving. You’ve got a 220mm fulcrum there on bearings. And the virtual pivot point is extended out another 150mm. I was able to reduce my tangent error down to around one degree by doing a bunch of things with overhang and null points. See
http://www.dvautier.com/nullpoint/null.htm

I can't imagine that bearing friction could be an issue in a well engineered/executed linear tracking arm. What's the relationship? 9" vs 12"? (psst!: 75% or 1.33 depending on how you look at it)
I feel that the common disregard for linear trackers is like racism: totally irrational

 

[SA-708]

One objective of tracking is reducing tangent error and liner tracking does this. But how much pressure on the outside groove wall does it take to move the cartridge. This is where pivot arms are better because they require very little force to keep the cartridge moving.

The arm on my linear tracking Technics SL-M3 also pivots, so the amount of force to move the cartridge is the same as any other pivot arm. It all depends on bearing friction and inertia from the mass of the arm.

 

[bimasta]

You probably didn’t feel like it standing outside while others could go in, but man, what a lucky kid.

Where I grew up, about the only place you could get to was a video game arcade. I got informed about jazz from my old uncle—really my dad’s uncle—stooped, sibilant and clacky speeched from dentures, a glass eye, shaky, afflicted with arthritis and Parkinson’s disease. He lived by himself and got around with the help of a walker as he shuffled everywhere in his tiny one-bedroom shack on a street corner a stone’s throw of the Lake Erie shore.

But he was a jazz drummer back in the roaring twenties. He got lessons as a schoolboy during WWI from a drummer who was sweet on his older sister trying to get in good with her. And he’d fill my ears with crazy stories about the old days and wild Prohibition Era and mob era gigs all the way up until, as he’d say, “The Parkinson’s got me!”

He taught me what he could with his numb, shaky hands, and when he could still produce a healthy sizzling drum roll on his padded dining room table, he’d still crack a grin and I swear both eyes, the real one and the glass one, would light up.

I eventually bought a very used drum set and brought it over to his house one day to see what he could still do. He could barely hold a coffee mug, but I sat him down, put his old sticks in his hands (I still have them—he’s been gone twenty years now) and he just started playing. And he played, and he played, and he played...

Naw, I enjoyed it. At 13, I didn't expect to get in, I didn't belong inside, so there was no disappointment or sense of exclusion — and man, Sunset Strip after midnight in those days was some of the best people-watching in the world.

Great and moving story about your great-uncle. And beautifully written — I could see his hands drumming on the padded table, see his glass eye light up.... You see with a writer's eye — ever do anything with this gift besides contribute to small audio websites?

And he played, and he played, and he played... and maybe still is...

 

[Nat]

I think considering bearing friction in a linear arm is totally rational, and I'm don't think that bringing in politically charged moral issues is in anyway helpful to the discussion.
Any arm, pivoted, linear, or whatever, needs some way of sensing when it is no longer perpendicular to the groove. That is usually the stylus, and it must move the arm enough for the sensor to register. So there will be some error - granted, in a properly designed and operating arm it will be very low. At that point, the arm need to move. If whatever bearings the arm is moved by are not already in motion, they need to start, and they need to overcome static friction which is much higher than sliding friction. So bearing friction is an issue. If the groove moved at a consistent rate across the record, this wouldn't be even a potential issue, but, of course, records are cut with constantly changing intergroove distances to account for varying volume levels which cause different amounts of groove modulation.
I have no disagreement with the idea that linear arms can have less tracking error than pivoted arms. It would be pretty pathetic is they didn't do better than a device, that at best, has two zero error locations across the disc. But my experience is that plenty of linear arms do much worse, usually because of maintenance issues - linear arms are complex, and most live and die by lubrication, which hardens and collects dust.
Pivoted arms have their problems, but those problems are there from the get go, and don't get worse simply by the passing of time. And there are pivoted arms that are widely considered to sound as good as the best linear arms (tastes differ, and all arms have problems - resonances, warp wow, ergonomics and so on - so you pick your poison). It's entirely legitimate and rational to discuss these issues.

 

[pfcs49]

@Nat: I'll agree with Aristophanes that less deflection occurs at the stylus to overcome gimbal bearings at the base of the arm if the arm (lever moment) is longer. That's just basic physics. But it's a red herring because bearing friction in a well engineered and construct arm (of any type) is very low. This is true-leverage counts (but not much!) for any type of arm, but amounts to hair splitting with the length argument.

I think considering bearing friction in a linear arm is totally rational, and I'm don't think that bringing in politically charged moral issues is in anyway helpful to the discussion.

Considering bearing friction in ANY arm is rational! However, as stated, in a well executed linear tracking deal, it's no more of an issue than in any other arm pivoting system. Your argument of static vs sliding friction seems contrived to me. Linear arms (with no mechanical sensor linkage, i.e.: optical and such) have exactly the same issues as pivoted; the arm bearings are in movement almost always, both vertically and laterally, very much as a conventional arm. Both have moments of motion in both axis and both directions as they track towards the record's end. And, both have similar bearings that can dry out or need servicing, so no difference there.
And, AFAIK, there is only one drag spec in each axis, not static and dynamic. Properly adjusted arm bearings have zero preload and zero play, thus virtually no drag or static friction whether conventional or LT.

As a LT enthusiast, I DO feel discriminated against by many audionerds, and it's arguments like above that seem, at least to my feeble mind, to be irrational and baseless, much like racism is. Sorry if you don't like the analogy, but if you've not joined the LT Tribe, you wouldn't understand!

 

[Nat]

Well, if you posit that a properly adjusted arm has zero preload and zero play, you are right. I just don't know of any mechanical device that actually has those qualities.

 

[sregor]

Seems to be a misunderstanding about arm movement with linear tracking arms. Most (from the Rabco SL8 to most current linear arms DON'T USE THE RECORD GROOVE TO MOVE THE TONE ARM. They have about a degree or two of motion around the tone arm base, and then have a sensor of some sort which moves the tone arm base to maintain tangential. The original Rabco used a switch sensor, which is one of its problem areas. The many arms which came out in the eighties used an LED sensor, which adjusted the arm tangential. My favorite system was the Mitsubishi design, which used a pair of LEDs in the base, and would move the arm to balance the output put and maintain tangency. The trick is to keep the tonearm base movement speed slow enough to not here it, and fast enough to keep the tangential error small. Even the mechanical systems like the SAT-4 and the HK tables use a mechanical assist to move the arm (a rubber roller on a rotating shaft. And if setup and working properly they sound really good., My 2 cents.

 

[pfcs49]

Well, if you posit that a properly adjusted arm has zero preload and zero play, you are right. I just don't know of any mechanical device that actually has those qualities.

I agree, actually. It's like "where is that point=0 on a number line, zero being that infinitesimal point between preload and play.
While we're talking about points my point is that both type arms that use 4 bearings have the same "problem" and that well executed, and adjusted, it's not a "problem"

 

[pfcs49]

Seems to be a misunderstanding about arm movement with linear tracking arms. Most (from the Rabco SL8 to most current linear arms DON'T USE THE RECORD GROOVE TO MOVE THE TONE ARM. They have about a degree or two of motion around the tone arm base, and then have a sensor of some sort which moves the tone arm base to maintain tangential. .

I don't think any participants here misconstrued your point.
I was waiting of someone to change the topic to static friction, etc, in the tonearm carriage (bearings) that the tonearm assy. tracks on, but as long as the argument is mute, everyone seems on the same page pretty much.

 

[Pio1980]

The Souther, Cantus, and pneumatic bearing arms are not servomotor and the groove transports the arm and cartridge. Friction is very low on the first two to essentially nonexistent on the third. Clearaudio has the rights to use the first two, Bruce Thigpen (Eminent Technology) perfected the third for the Infinity pneumatic bearing linear turntable.
Seevomotor linear tracking arm turntables use a short pivoted arm with an error correcting feedback sensing arrangement and are essentially frictionless.

 

[pfcs49]

I've always wondered about those air bearing linear trackers.
The vertical effective mass could be quite low, but in the lateral it's the mass of everything that moves on the bearing which is very high I'd think.
OTOH, the lateral resonance point would be incredibly low!

 

[sregor]

I don't think any participants here misconstrued your point.
I was waiting of someone to change the topic to static friction, etc, in the tonearm carriage (bearings) that the tonearm assy. tracks on, but as long as the argument is mute, everyone seems on the same page pretty much.

I see your point. I over reacted when people start going on about friction in a tangential arm system. Done right, it shouldn't be a factor (i.e. it is a moot point). I would opine that the biggest problem is one that does it silently - mechanical isolation of the base drive from the tone arm, and that is what separates the good tangential arms from the not so good.

 

[Pio1980]

I've always wondered about those air bearing linear trackers.
The vertical effective mass could be quite low, but in the lateral it's the mass of everything that moves on the bearing which is very high I'd think.
OTOH, the lateral resonance point would be incredibly low!

Bruce made that adjustable on the ET arm, the pneumatic arms are always moving when tracking a record.

 

[restorer-john]

We had a good discussion in this very subject earlier this year. I can't seem to find the thread right now.

I stand by what I said in that thread, essentially: There has to be an error before the tracking system moves the arm. Some decks (regardless of price) need a quite significant error before operating the arm mechanism and many move in bursts and overshoot. Many systems are noisy.

I wish there was a perfect linear tracker, but every single one I've owned (and that's quite a number) have been flawed in one way or another. Some highly regarded ones are utter junk IMO.

Because of that, I keep them for 'play', not for listening.

 

[pfcs49]

Bruce made that adjustable on the ET arm, the pneumatic arms are always moving when tracking a record.

Do you mean that the arm air bearing has enough play for the arm to move laterally at the stylus while not at the bearing, effectively de-coupling it so lateral and vertical effective masses are equal or virtually so?

 

[sregor]

There has to be an error before the tracking system moves the arm.

But done right, they still will be less than the tracking error of a pivoted arm.

Some decks (regardless of price) need a quite significant error before operating the arm mechanism and many move in bursts and overshoot. Many systems are noisy.

These are engineering issues, and done right, they are surmountable. I will concede that not many do.

 

[Pio1980]

Do you mean that the arm air bearing has enough play for the arm to move laterally at the stylus while not at the bearing, effectively de-coupling it so lateral and vertical effective masses are equal or virtually so?

Not specifically, but play at a microscopic level is possible at low manifold pressure. At horizontal resonance, the entire arm assembly would vibrate laterally. The counterweight has variable coupling for tuning out such resonance.

 

[Nat]

In an air bearing arm, the friction is incredibly low, but generally the mass of the moving system - the arm and the air bearing - is fairly high, and unlike mechanical arms that use some sort of method of propulsion to react to the error signal, air bearing arms are moved by groove, and given the variations in groove spacing, the inertia of that lateral mass can be significant - resisting speeding up and then resisting slowing down. Certainly this was an issue that concerned the arm designers who worked hard to lower that mass.
Of course this is also true of all pivoted arms, and seems to be handled well enough by most arms of both types.