Angling for 90° - tangential pivot tonearms

[directdriver]

More pictures of the SL5 arm.

Goldmund also introduced the same arm called T5 under their name, usually mated with the Goldmund Studietto turntable.

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[directdriver]

Goldmund T5 arm installed independently, on a DIY turntable!



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[tade]

I have a similar plan as to that goldmund. It is going to be a short unipivot arm, with a mirror mounted perpendicularly over the pivot point. I will mount a laser/reciever on one end of the track, and bounce the laser off of the mirror and against a photodiode to control the speed. The speed feedback will not be on/off, but proportional to offset. This system should assure smooth travel, and perfect azimuth to boot.

Excited to see that!

[berlinta]

@walterwalter: A groove modulation figure from zero to, say, 50 µ will require a change in antiskating force of about 2-4%, itself inseparable from the friction coefficient of the vinyl used for a particular record. The difference between vinyl formulas is (generally) greater than that caused by modulation variation. Since music usually changes in level all the time , the only way to create a - close to - "perfect" antiskating mechnism would be using a strain gauge cartridge and taking the net deflection of the gauges as the value on which to base the application* of a compensating force. *like the servo controlled pivoted arms of the 80s (Sony Biotracer, JVC, etc...). Except those took a preset value and tried to maintain it. Real time values can only be obtained from a strain gauge cartridge. Skating compensation is flawed in principle because all known mechanisms apply the force at the pivot point, not the stylus. Less than perfect bearings and a certain eff. mass will cause the cantilever to be deflected(unevenly loaded), throwing the mechanical symmetry of the generator(in the horizontal plane) out of balance.
@directdriver: You'd be well advised to leave the original armwand/bearing assemblies on the Lurne/Goldmund arms. They are vastly better(less resonant) than the Clearaudio Satisfy.

I've played for years with the idea of providing a base to convert pivoted arms to linear trackers. The fact alone that most pivoted arms are not surface mount designs and the difficulty altering the headshells or being able to lower the arms sufficiently kept me from doing it. Nor did I like most of the conventional arms sonically... would you put a bigger engine in a car that had a weak frame from the start? And the added complexity has its price(literally).
Anyway, Ralfs arm is, for the most part, the only design that tries to address nearly every geometrical issue related to tracing a record(conceptually superior to all commercial arms that travel on a line parallel to a radial line). Now Ralf, if you would only loose those carbon fiber tubes ;-)

Good night,

Frank

[berlinta]

@tade: What's the connection between the system you're describing and perfect azimuth?

Did you mean zenith or tangency instead?

Frank

[tade]

Berlinta,

So long as you set up the laser/reciever such that the headshell is level, any later change in azimuth should cause the laser to no longer fall on the reciever properly. It would be obvious then that something was amiss.

I would mount the laser/reciever as far away from the tonearm as possible. If you mount it a foot away, that is two feet of beam path. This could be much more sensitive to a change in angle than any of the other designs I have seen.

Thoughts?

[Conrad Hoffman]

Yes! That SL-5 is exactly on the lines of what I've been thinking about- thanks, never seen it before. No doubt, it too is far beyond my means.

As for laser and other position feedback, if you do the design right the sensitivity will be so high that there's no need for any extra beam path. The problem I worry about is manual cueing. I want to be able to grab the headshell and cue with the action no different from any manual arm.

? Tangential (be it pivoted or not) arms have no skating problem by definition.

Oshifis, I don't believe this is correct unless you mean the entire arm is tangential, and that traditionally wouldn't be pivoted. Unless you remove the offset, placing the pivot directly in line with the stylus, all the anti-skate issues remain. Think of any standard pivoted arm where you adjust the cartridge for perfect alignment at some arbitrary point on the record. That's no different than what most of these parallelogram arms do. They still have offset.

Nor did I like most of the conventional arms sonically...

Berlinta, maybe without the offset you'd find the character of the arms changed significantly. IMO, that's the big question that only building the thing can answer!

[directdriver]

berlinta: "You'd be well advised to leave the original armwand/bearing assemblies on the Lurne/Goldmund arms. They are vastly better(less resonant) than the Clearaudio Satisfy."

Frank, I do not own the Lurne tonearm and I was NOT encouraging people to butcher an existing product. I was only suggesting if one builds a similar gliding arm-base along the line of the Lurne and Conrad Hoffman's idea, one can mount a conventional arm on it and the reason I suggested the Clearaudio Satisfy because it uses a rotatable headshell (Schroeder clone??) that can straighten the offset angle and its vertical bearings are not angled +-23° like many pivot arms and it's also not terribly expensive so DIYers can afford. I supposed one can also use a Rega or straight tube Jelco or any other budget arm for experiment. Mr. Lurne is a talented designer and I would not want to alter or butcher his product. Again, the suggestion was for a diy project only not existing product.

berlinta: "I've played for years with the idea of providing a base to convert pivoted arms to linear trackers. The fact alone that most pivoted arms are not surface mount designs and the difficulty altering the headshells or being able to lower the arms sufficiently kept me from doing it."

I understand the difficulties. With the proliferation of thick tall platters, it is possible to have enough height to mount a conventional pivot arm on the base without lowering the platform. If a plinth is not too big or wide, it is possible to mount the base on an arm-pod with an elongated hole for the mounting hardware to drop through so arms do not have to be surface mount design -- imagine a carriage or wagon on two rods with a wide hole in the middle. More and more arms are using headshell of your design, the Schroeder style headshell, so altering the headshell is not that hard, if we choose the arm wisely. Bottom line: it is totally doable. And I would love to hear the difference between a pivot arm in a conventional set up and in a "linear mode" set up.

Thanks for all the ideas and suggestions, Frank!

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[directdriver]

Conrad Hoffman: "The problem I worry about is manual cueing. I want to be able to grab the headshell and cue with the action no different from any manual arm."

I think if we implement the sensor mechanism closer to the pivot area (like the Rabco) or at the back close to the counterweight, it would not affect cueing like the sensor at the headshell area or at least not as awkward.

Anyway, your idea is totally doable!

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[walterwalter]

Berlinta: " Skating compensation is flawed in principle because all known mechanisms apply the force at the pivot point, not the stylus. Less than perfect bearings and a certain eff. mass will cause the cantilever to be deflected(unevenly loaded), throwing the mechanical symmetry of the generator(in the horizontal plane) out of balance".

To Berlinta, one more question, trusting your experience. I already figured out technical solution for close to "ideal " antiskating compensator for one record(or, let's assume, it's statistical approximation). Keeping in mind all inherited problems you mention, would those irregularities on different records be still audible (if I'll succeed with this design and apply it)?
Or it is better get rid of skating problem at all and move to purely tangential design (I've already figured out that one too)? Been mechanically inclined, rather than electronically, I've chosen mechanical tracking and dragging principle.
However, for DIY-ers here, those who thinks of electronically guided one, I would suggest to consider CD-LD-DVD tracking solutions, those there seems to be using constant and smooth transition of laser pick up head, instead of sporadic movement with most of tangential tone arms...