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Old 27th April 2010, 04:57 PM   #1
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Default Angling for 90 - tangential pivot tonearms

There has to be a way to get that 90 degrees on a stylus without the damn air pump!!


I don't want to go off track in other tonearm threads so I decided to start a new thread focusing on the discussion and design ideas for pivot style tonearms that can attain tangential tracking, a pivot linear tracker if you will. Sounds like an oxymoron but it can be done.

To be brief, most tangential tracking tonearms are typically air-bearing tonearms that allows the stylus glide across the radius in almost frictionless manner to simulate how a record is cut on a lathe. Other means of this gliding action can be also achieve via linear bearings like rollers on a rod or bushing on a rod, etc... Some concept arms even suggest using floating opposing magnets. The flaw of such tonearm is that the horizontal mass is enormous regardless of bearing quality, low friction or no friction. It limits the choices of stylus, depending on its compliance. And the use of an air pump is not for everyone to say the least - a personal pet peeve of mine. The genre of electronic servo detection pseudo-tangential trackers like the Rabco tracking across the record in tiny little arcs constantly self correcting its way to the end of the record is not part of this discussion here. Anyway, this thread is NOT about the above tonearms. We want to talk about pivot tonearms that can track tangentially by changing stylus angle simultaneously.

The best examples are actually currently available in production. By now, many people have heard of the Thales tonearm from Switzerland. It is a pivot style tonearm with an extra pivot at the headshell area right above the stylus. The changing angle is always 90 degree to the radius because it is part of a triangle that is inside a semi-circle that adheres to the Thales theorem, that is, "Thales discovered that the circumferential angle subtended by a triangle in a semicircle is always a right angle. As a result, the half circle above the hypotenuse of a right-angled triangle is called the Thales Circle."

http://www.tonarm.ch/kommentare/thaleskreis_e.html

6moons industryfeatures: Thales

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With the basis of the Thales Circle, the designer Micha Huber devised a tonearm that can track any point inside the semi-circle always 90 degrees to the center of the record, voila a linear tracking tonearm that pivots without any linear motion. Genius! The tonearm appears to be executed with quality construction and precise worthy of a Swiss watch. So far it is the ONLY tonearm on the market that is capable of 100% geometric accuracy in maintaining tangency, at a price,of course, as it sells for, I believe, 6000 .

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Visually, it has the look of a Rube Goldberg device but looking closely, everything seems to have its specific function for good reason. I don't want to write a white paper on the Thales design but for those who are interested in examining it more closely, feel free to explore its website. But this tonearm does give a good example of the objective here.

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Thales will introduce a new tonearm named "Simplicity" that looks simpler and elegant and even though it is not 100% accurate in geometry but it reduces the tracking error to a maximum of 0.008! Pretty damn good in my book.

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There are historical predecessors of such design and one can find that in the classic Garrard Zero 100.

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And the Burne-Jones arms.

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One can also find examples in contemporary designs like the RS Labs RS-A1 arm with a pivoting headshell.

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"Prototype of the 'Bajulaz' tonearm on a TD-124. It was designed by Ing. Bajulaz to overcome the geometry problems of the conventional tonearms, but allegedly it wasn't so good for the new stereo cartridges and therefore never went in production."

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I will continue to upload more pictures and present ideas to stimulate discussions and, hopefully, inspire the DIY spirit.


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Old 27th April 2010, 05:13 PM   #2
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More Thales tonearm pictures.

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Old 27th April 2010, 05:21 PM   #3
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Click the image to open in full size.

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The above is a diagram of the working of the Thales arm. Now, if I eliminate the arm from M to C completely, what is left is the triangle inside the semi-circle that C is always tangent to A. The hitch is that we have to come up with a design to allow the distance between to B to C to change about couple inches. In this case, there's no need for any pivot or bearing at the headshell area at all, just a straight wand. We can have a fixed arm length and the arm's base sit on some linear motion bearing or a tricycle platform that can move front and back and the middle wheel to steer the tricycle in a curved track that allows the arm to be tangent to A at all time. Essentially an assembly that allows pivoting and linear motion at the same time.

Look at picture below and I hope this makes sense.

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Old 27th April 2010, 05:37 PM   #4
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Arm in motion

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Old 27th April 2010, 06:09 PM   #5
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IMHO, all mechanical nightmares that probably introduce as many problems as they cure. Here's what I've been thinking about, but have yet to build. Pivoted tone arms are highly developed and work well, but I think that offset introduces forces that cause more trouble than can be fixed with anti-skate mechanisms, not to mention the obvious problem of getting the angle right at only two points. Rotating the head of an offset arm is not the answer! You must eliminate the offset. So, keep the standard tonearm, remove the offset and make it a bit longer. Now, just drive the pivot assembly along the back of the turntable in a track. Servo it, probably photoelectrically, but don't try for perfection. Let the tonearm do what it was designed to do. Try for silence and smoothness on the drive. I'm not sure what the best drive method would be, maybe a lead screw and DC motor, maybe a thin thread and drum drive or even a linear motor track. This is basically an electronic forum, so moving the pivot under motor control shouldn't be too difficult. The angular error will be very small even if the pivot location is off a couple mm- no human can align a cartridge that close regardless of what they claim. Maybe line the track with Teflon tape and/or make it a V-way for better stability. IMHO again, any system that tries for a rigid coupling between the tone arm and track (like air bearing arms) creates a horizontal mass problem that's completely unnecessary. The arm in this design can be a unipivot or whatever you like.

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Last edited by Conrad Hoffman; 27th April 2010 at 06:13 PM.
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Old 28th April 2010, 08:04 AM   #6
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Quote:
I think that offset introduces forces that cause more trouble than can be fixed with anti-skate mechanisms
I agree. I think many audiophiles prefer the sound of linear trackers is, perhaps, due to the elimination of offset angle and anti-skating in pivot arms.


Quote:
Rotating the head of an offset arm is not the answer! You must eliminate the offset.
I don't know if you are referring to the Thales arm or the other above arms but all the arms I mentioned earlier does NOT have an offset angle and the stylus is NOT tracking with overhang, since it is pivoting in an arc the headshell towards the spindle it is constantly rotating in tangent and there is not skating force created, therefore NO antiskating mechanism is needed.


Quote:
keep the standard tonearm, remove the offset and make it a bit longer. Now, just drive the pivot assembly along the back of the turntable in a track. Servo it, probably photoelectrically, but don't try for perfection.
What you are suggesting is really ending up with a servo tonearm like the Rabco or the Goldmund. And that's not what I have in mind and as I said at the beginning of this thread that I don't want to resort to motor or air pump. What I want is to think to come up with something geometrically clever and simple at the same time. That's where the creativity comes in.

However, just to indulge you for a second, I have thought of something along similar line is to create a gliding armboard that allows a conventional pivot arm to work as is but to servo correct the microscopic out of tangent arcs via motor and sensors. There are linear motion guides and bushings out there that have no slops that are quiet and smooth such as products from THK. Not all pivot arms are good candidates to be mounted on such motorized gliding armboard because some arms have offset headshells that are not suitable for this operation and arms with J-shaped or S-shaped armwands make matters worse. But the worse is the kind with offset bearings at the pivot point. Looking through available modern tonearms to find a good candidate for such experiment, one must find an arm with straight wand, no offset headshell, and no offset bearings. And the best arm I can think of right now is the Clearaudio Satisfy arm because it has a rotatable headshell, straight armwand, no offset bearings. And one can easily defeat the antiskating mechanism. The arm itself is visually quite elegant looking too.

I think the rotatable headshell allows for experimenting with adding a pivot point about the stylus to turn it into an RS Labs RS-A1 type of arm. Just a thought.

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Last edited by directdriver; 28th April 2010 at 08:27 AM.
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Old 28th April 2010, 05:34 PM   #7
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Some images of pivoting headshell from RS Labs. Without any guiding mechanism, I do not believe just by having a pivot headshell will give us less tracking error but this is just for showing how a pivot mechanism can be implemented on a headshell, no more no less.

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Old 28th April 2010, 06:29 PM   #8
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Some patents on how to pivot the headshell:

Pivot headshell patented by Wolf

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Pivot headshell patented by Van Eps

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Old 28th April 2010, 07:20 PM   #9
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Garrard Zero style tonearm patented by Klein


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Old 28th April 2010, 07:54 PM   #10
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More discussion of linear tracking arm from Yosh in Japan.

http://www7a.biglobe.ne.jp/~yosh/lineartrack.htm via Google Translate


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