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Linear tracking - a myth debunked?

niklasthedol said:
You can go back to the pictures I posted in this thread and get clarification.

"dolph"
Click to expand...

HI,
Please, I'm not trying to bait you at all. I don't understand what you are saying. I have looked at your pictures. While I have very serious reservations about the usefulness of those arms, I do understand they develop zero (approximately) tracking error. I find them interesting. But, because the pivot is off to the side, I think they will develop skating force which, of course, is impossible with a linear tracker. Thus, I'm defining skating force as a benchmark characteristic of a linear or tangential tracking tone arm.

So, I'm in need of an explanation of the geometry. I think this question and discussion is well at home in this thread.

Sparky
 
Karma16 said:
HI,
Please, I'm not trying to bait you at all. I don't understand what you are saying. I have looked at your pictures. While I have very serious reservations about the usefulness of those arms, I do understand they develop zero (approximately) tracking error. I find them interesting. But, because the pivot is off to the side, I think they will develop skating force which, of course, is impossible with a linear tracker. Thus, I'm defining skating force as a benchmark characteristic of a linear or tangential tracking tone arm.

So, I'm in need of an explanation of the geometry. I think this question and discussion is well at home in this thread.

Sparky
Click to expand...

What makes you think it is the skating force laying behind the definitions?
Tangential arms have side moving force too.

"dolph"
 
cactuscowboy said:
Just a comment from personal experience.

My Beogram TX-2 (a linear tracker) is hand's down the best tracking turntable I've ever owned. It will track warps and damaged grooves better than pivot tonearms.
Click to expand...

What's a fair used price for a TX-2? What problems might I expect to have with a used one? If repair is needed what company still works on them?

Thanks
Bart
 
niklasthedol said:
What makes you think it is the skating force laying behind the definitions?
Tangential arms have side moving force too.

"dolph"
Click to expand...

Hi,
Some, but very little and it depends on the design. My Eminent Technology ET-2 air bearing arm has almost none because the bearing is essentially fiction free. The only side force in this case is that which is related to the inertia of the arm as the groove pulls it across the record. Because of the constant nature of the groove acceleration of the stylus and arm, inertia is very small. Thus, the side force is very small. While servo type linear arms have more side force it is still very small compared to a pivoted arms skating force.

Skating force is an entirely different thing. It is caused by the offset angle of the cartridge mount, the off center location of the arm pivot and groove friction acting on the stylus. If you work out the force vectors you will see that skating force is not small at all. It is very significant. This difference, that is, the side force of a linear arm verses the skating force of a pivoted arm, is why I claim that the lack of skating force is the characteristic that can be used to define a linear tracking arm.

To reinforce this notion, for many years I have monitored stylus wear on a variety of arms using a Shure purpose designed laboratory stylus microscope which I used professionally in my repair business and personally on my own equipment. I have observed thousands of styli.

The difference in wear patterns between a linear arm and a pivoted arm is striking, obvious and consistent. On the microscope, wear is indicated by the size of the flat spots where the stylus tip contacts the groove and friction grinds on the stylus. I call these wear facits.

There are two facits that correspond to the inner and outer groove sides and, thus, the inner and outer sides of the stylus. In all cases, the facits shown by styli used on linear arms are perfectly symetical. That is, they are the same size and shape. In all cases, the facits shown by styli used on pivoted arms are asymetrical. The inside facit is usually at least twice as big as the outside facit. They are shaped differently too.

Why is this? Because the linear arms generate no significant side force and no skating force. Thus, the stylus sides wear evenly. Pivoted arms, however, generate skating force which cause the sides to wear unevenly. You do recall that skating force cannot be properly compensated because the groove friction is constantly changing causing the skating force to constantly change.

Your comments are welcome.

Sparky
 
Karma16 said:
Hi,
Some, but very little and it depends on the design. My Eminent Technology ET-2 air bearing arm has almost none because the bearing is essentially fiction free. The only side force in this case is that which is related to the inertia of the arm as the groove pulls it across the record. Because of the constant nature of the groove acceleration of the stylus and arm, inertia is very small. Thus, the side force is very small. While servo type linear arms have more side force it is still very small compared to a pivoted arms skating force.

Skating force is an entirely different thing. It is caused by the offset angle of the cartridge mount, the off center location of the arm pivot and groove friction acting on the stylus. If you work out the force vectors you will see that skating force is not small at all. It is very significant. This difference, that is, the side force of a linear arm verses the skating force of a pivoted arm, is why I claim that the lack of skating force is the characteristic that can be used to define a linear tracking arm.

To reinforce this notion, for many years I have monitored stylus wear on a variety of arms using a Shure purpose designed laboratory stylus microscope which I used professionally in my repair business and personally on my own equipment. I have observed thousands of styli.

The difference in wear patterns between a linear arm and a pivoted arm is striking, obvious and consistent. On the microscope, wear is indicated by the size of the flat spots where the stylus tip contacts the groove and friction grinds on the stylus. I call these wear facits.

There are two facits that correspond to the inner and outer groove sides and, thus, the inner and outer sides of the stylus. In all cases, the facits shown by styli used on linear arms are perfectly symetical. That is, they are the same size and shape. In all cases, the facits shown by styli used on pivoted arms are asymetrical. The inside facit is usually at least twice as big as the outside facit. They are shaped differently too.

Why is this? Because the linear arms generate no significant side force and no skating force. Thus, the stylus sides wear evenly. Pivoted arms, however, generate skating force which cause the sides to wear unevenly. You do recall that skating force cannot be properly compensated because the groove friction is constantly changing causing the skating force to constantly change.

Your comments are welcome.

Sparky
Click to expand...

Thank you for welcoming my comments.

I have, for the time being, five worn down cartridges, all being used in pivoting arms.
I have taken pictures of the for fun with electromicroscopes with different magnifying ............whatever it's called in english. :-)

I also have magnifiers I use when I work on mechanical watches.
There seams to be no asymetrical wear on my cartridges.

I suggest the reason of the asymetrical wear you experience is due to misallignment and unfortune adjustments of the set-ups.

All set ups are offering one compromise after another.
Nothing in audio is without compromise and nothing is perfect.
I find that the linear tracking pivoting arms should have more attention and developed further.
It might be or become the best compromise of them all.

"dolph"
 
HI,
Sorry, I must disagree. While some may be due to that reason, I have seen, I repeat, thousands of styli. I'm confident in my observations.

Are you saying that skating force will NOT cause what I described? If so, you are kidding yourself.

Sparky
 
Thank you, Sparky, for a most informative post! I have wondered about the wear patterns you report (for years), and your comments are the most definitive I have ever found.
 
oh man, someone locally is selling that crazy Revox for 500$

Is it actually worth that much?

edit: not in a dollars and senses kind of way, more in a curiosity on my end kind of way
 
BartJY said:
What's a fair used price for a TX-2? What problems might I expect to have with a used one? If repair is needed what company still works on them?

Thanks
Bart
Click to expand...

Bart,

I bought my TX-2 new back in 1989. It was my sole turntable for 19 years and saw continual use, spinning at least 3-4 LPs every day. Aside from cartridge replacement (which is expensive) I only replaced the belts once. Note that there's two belts. One to drive the platter and a smaller one for the tonearm. After 20 years the smaller belt broke!

The only other problem resulted from a dumb-ass mistake I made. I placed the turntable directly on top of a receiver. After playing a few LPs at high volume, the turntable's speed became erratic, slowing down considerably and then stopping altogether. When I touched it, it was very hot, from sitting on the receiver.

I removed the platter, gaining access to the circuit board inside. Spotting a larger electrolytic capacitor, I decided to replace it, just on a hunch that it was the problem. I bought a new capacitor at Radio Shack, soldered it in, and it fixed the problem. :banana:

I can't tell you what a used TX-2 would sell for, but it would probably be cheap. The main drawback with most B&O turntables (including the TX-2) is that they use proprietary cartridges. They're no longer available from B&O, but Soundsmith offers their excellent cartridges based on this design. My Soundsmith SMMC-2 cost about $425 two years ago. Soundsmith does offer less expensive options, but they're still relatively pricey.

As for repair (if needed), I couldn't tell you. I live in NW Wyoming, so I pretty much have to fix every piece of audio gear myself, or just give up and throw it away. So, I'm a novice electronics repairman, not by choice, but by necessity.
 
Karma16 said:
HI,
Well, one way to define a linear tracking tone arm is if it develops skating force. True linear arms do not. The Zero 100 does along with a lot of other nasties. It does not belong in this thread which has so many fine linerar designs.

Please, start your own thread.

Sparky
Click to expand...

:rolleyes: :rolleyes: :rolleyes: :rolleyes: :nono:

No thanks.

I constantly learn something new. Continue my education. :scratch2: , especially on the Zero100, have you ever owned one? Regards.
 
I actually find it fruitful to have both linear tracking and articulated pivoted arms discussed in the the same thread. Clearly there are differences in approach, but some of the aims and some of the benefits are the same, though the penalties seem to be different.
 
Tonearm Design Objectives

If I am not mistaken, all/most tonearm designers strive to move the stylus tip in a straight line across the record surface.

In the world of mechanics this is called a linear movement (not argueable, right?). Well, maybe there is a nonlinear movement in the direction of travel due to groove modulation, bearing friction etc, etc.

Why is this desirable? One reason, stylus/groove destruction, as Sparky noted with his microscope. Can we imagine/guess what the record groove looks like?

Another reason descrbed by Erik Loefgren in 1938, audible distortion. He demonstrated mathematically the harmonic distortion created by stylus tracking/tracing errors. He also subjectively noted the "dirtiness" sound of complex symphonic music due to tracking errors.

I conclude that all tonearm designs are foremost, linear trackers by design. Some designs are better than others.

Draw your own conclusions.

Regards. Peace.:music:
 
Karma 16: Not trying to get in a squabble, but it seems to me that linear arms have to put some force on the outer groove wall either to actually move the arm, as in air bearings, or to take the arm out of true tangency, so that the mechanism knows to move the arm, and so perfectly balanced wear seems impossible. Am I wrong in thinking of it this way, and if so, why?
 
Obviously friction with the groove, and with skating force making the issue more complex. I was not trying to suggest that pivoted arms don't have uneven wear patterns -- that would be just as stupid as you obviously think it would be, since its commonly noted as a problem even with more or less correct antiskating force applied.
What I'm asking is how its possible that linear arms create perfectly symmetrical patterns -- some force has to move the arm across the record.
 
I'll take a stab at answering this, from an engineering perspective. Let's start with a tonearm that has the stylus exactly in line with the pivot point. Let's take a record that's not turning and set the needle in the groove. The needle is at position A. Now rotate the record slightly to position B. The needle must move inward (or else jump out of the groove) because the radius of the "circular" groove is decreasing. This movement doesn't come from a centripetal force, it's the force of an inclined plane (a wedge if you will). The tonearm by necessity has now pivoted a little.

Linear trackers--at least like my Technics SL-5--actually still have a pivot point. They also have a sensor that detects that the tonearm has pivoted very slightly. The turntable then moves the pivot point of the tonearm inward slightly; the pivot point assembly rides on a linear bearing and a slow-speed motor moves the tonearm assembly. The tonearm moves ever-so-slightly past the new ideal position, allowing the tonearm to go from a position slightly outward, to perfect, to slightly inward, before the process starts again. The movement is tiny, so the tonearm is never very far out of the ideal position.

The antiskating force comes into play on "non-linear" pivoted tonearms; the needle is not in-line with the pivot point. There is an offset, by a certain distance (d). This can be seen by looking at the tonearm, and drawing a line from the angled tonearm head past the pivot point, and measuring the distance that this line misses the pivot point. On my Dual 1225 it appears to be about 75 mm, or 3 inches approximately.

Now spin the record. The needle isn't frictionless, there is a tiny drag on the needle. The coefficient of friction between the diamond stylus and the vinyl is very low, but it's not zero, plus the needle has to go up the ridges of the groove (of course then it goes back down again too). If the groove were perfectly smooth, the force of the drag would be the coefficent of friction (COF) multiplied by the tracking force. Let's say the COF was .1 for diamond on vinyl, and a tracking force of 1.5 grams; the force of the "drag" would be 0.15 grams (note grams isn't really a force, but a mass, the force is actually 0.0015 Newtons). This drag, being off-center from the pivot point, will attempt to make the tonearm pivot inward. The torque is the distance times force, or 75 mm times 0.0015 Newtons...that equals 0.11 N-mm which is pretty darn small, and if I did my math right. But the anti-skating is an opposing torque which attempts to counteract this inward-acting torque. Whew.
 
nashvillebill said:
Linear trackers--at least like my Technics SL-5--actually still have a pivot point. They also have a sensor that detects that the tonearm has pivoted very slightly. The turntable then moves the pivot point of the tonearm inward slightly; the pivot point assembly rides on a linear bearing and a slow-speed motor moves the tonearm assembly. The tonearm moves ever-so-slightly past the new ideal position, allowing the tonearm to go from a position slightly outward, to perfect, to slightly inward, before the process starts again. The movement is tiny, so the tonearm is never very far out of the ideal position.
.
Click to expand...
Excellent explanation.:thmbsp:

My Phase Linear (Pioneer) does pretty much the same.. detects any slight movement with a sensor, in my case a light source and photocell that detects any change from a "shutter" that's attched to the pivoting tone arm, a fraction of a degree, which is amplified and drives the stator coil part of the linear arm motor which moves the tone arm base in a straight line on rollers. It is interesting to watch how it handles a slightly eccentric record, which is quite well! Whole arm base will move slightly side to side with the movement of the record.
 
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