Angling for 90° - tangential pivot tonearms

MØRCH DP-8! I did not know about it. The design is quite convincing and, most of all, one can easily add these side weights, increasing the 'horizontal effective mass' only, in some DIY pivoted tonearm experiment!

As for the cartridges compliance, I feel that special designs would be needed, with significantly different compliance values in the horizontal and vertical directions..
 
Well. Niffy, I am quite convinced on the benefits of the increased tonearm 'lateral mass'. I may not take special measures to increase my 32 g one, but I will feel free to add some more grams due to useful changes, e.g. replacing the plastic screws with metal, applying more heavy, but finer bearings and building a more stable and stiff boat construction. My new detailed measurements show that the rolling noise of my boat is really very low and the horizontal friction at the 1 mm/s speed levels is about or below 5 dyne. I will post these results later. Greetings!
 
A good take on skating (and tonearm design in general) can be found in this article by Marc Gomez of Swedish audio technology.

https://hypercomments.com/api/go?url=http://swedishat.com/SAT 9" vs 12" paper.pdf

Niffy

Very good reading. I can’t agree more for following statements.

The function and performance of an arm is therefore best analysed by its behaviour from a mechanical point of view, as a mechanical precision instrument rather than a musical instrument.

The 2nd statement is especially true for a floating arm.

It is fundamental to understand that every relative movement of the stylus with respect to the cartridge body will generate a signal - it doesn’t matter whether the movement comes from the stylus or the cartridge.

However, Mr. Gomes completely disregarded the reductions of tracking errors on a 12” pivot arm, but put emphasis on the vibrations caused by extra 3” long of arm wand on 12” pivot arm. I find it is difficult to agree with that. If I have to use a pivot arm, 12” is a must.
 
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This one seems a bit better, to me. (you know it for sure)
http://brujic.gradjevinans.net/HiFi/ve_skating_force_and_antiskating.pdf

Detailed examination of the factors that determine skating, detailed analysis of the force breakdown, calcs corroborated by measurements and practical observations. Data and behavior quite near to those that could be observed even with my crude kitchen-table pendulum (#1548-1569-1595, if physicists may forgive me).
No trace in those formulas of the - tracking error - that would affect Gomez "Linear Offset" (what? how?), when at most it can have a minimal effect on the stylus drag. Also the calcs for the antiskating torque as independent by the shaft length seem doubtful (r does not change as the sinus of the angle, or not?)

Although being a fan of TA rigidity, and of 9" arms (...so cute) like Herr Gomez, that seems to me yet another leaflet pro domo sua type. Maybe those who believe in decoupling + damping on trembling 20" arms could produce equally valid ones: there are dozens around.
Recently when reading these so learned demonstrations sometimes reminds me of the fable of the fox and the unripe grapes. In advertising it's called "selective exposure", we only listen to what confirms our opinions, especially when they falter.

carlo
In the last part of the pdf there is an interesting overview of anti skating devices (but the simple, variable Mikroseiki is missing) and of dynamic correction efforts, which more or less is the way I would like to go, even if in a different way.
 
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However, Mr. Gomes completely disregarded the reductions of tracking errors on a 12” pivot arm, but put emphasis on the vibrations caused by extra 3” long of arm wand on 12” pivot arm. I find it is difficult to agree with that. If I have to use a pivot arm, 12” is a must.

Hi Jim,

We don't disagree on many points but we do on this one.

He doesn't disregard the difference in the tracking error between 9" and 12" arms. What he says is that compared to things like the manufacturing tolerances of the cartridge the difference between the two arm length is not very significant. I completely agree with him that the large increase in rigidity and the higher resonant frequency of the shorter arm makes MUCH more difference than the small improvement in tracking error of the longer arm. He does stress the point that the 9" version of his arm sounds better. If I have to use a pivot arm, 9" (or shorter) is a must.

The reason I made a linear arm was not to decrease lateral tracking errors. I wanted to push the rigidity and resonant frequency of the arm as high as possible. In order to achieve this required making the arm very short. Making the arm very short dictated that the arm had to be linear tracking. Any decrease in lateral tracking error is just a bonus.

Niffy
 
www.esperado.fr - Une idée de bras radial
bras-def-petit-meca.gif
 
From my previous link - attachment
Someone knows how this strange arm works?

From drawing and description seems that the traction exerted by the stylus drag trough the wand on the ring 5, is compensated by the inclination of the balance member 12 on his pivot 15.
I cannot see any other consequence than a continuous variation of the overhang, which could have only harmful effects. Strange, improbable from a respected designer.
But if there is an anti skating or geometry effect, or a variation of pivot resistance (which is what interests me presently) really I don't understand how it could work. (not so strange)

carlo
 

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  • percy wilson TA 2.jpg
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Thanks a lot Ray, beautiful documents; your TA knowledge seems endless.
Maybe i got it, once read his description. Seems simple and sophisticated, just a matter of planes of tilting of the "balance member": not on the azimuth as i thought, but slanted due the " push pull" (the stylus drag) acting at the offset angle.
Now i'll try to evaluate well the consequences of that design. Even the construction is filled of uncommon ideas (like the pneumatic unipivot etc.).
This arm pose really many challenges, and deserve to be further investigated: that man, more than half a century ago, had really a clear vision of the tracing problems.
carlo
 

Thanks for chiming in.

The designer Christophe Esperado was a one time member of the forum (now banned) and participant of this thread and introduced this arm in post#225.

The arm is another variation of the Birch geometry discussed earlier and it uses a servo system to move the arm base, which I think has great potential as opposed to a parallel tracking servo. The similar arm in modern production would have to be the Reed 5T arm.
 
...going off topic?
Hi friends, first of all I have to ask Directdriver (and then you all) if the research for geometries and/or passive devices tending to cancel (not compensate) the skating (balancing it with the side force, in order to avoid left or right bending) may be considered part of the target of this thread, dedicated to PLTs, and tending to eliminate the offset as main cause of the skating.
That is, if it's the enemy, or how to beat him that counts in this battle. Admitted, and not granted at all, that we can succeed.

thanks - carlo
yesterday I did a simplified 3D model of the Percy Wilson TA, which however does not seem to fully confirm the claims of the Wilson patent, but I will not talk about without permission