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Old 9th February 2018, 04:54 AM   #1711
2wice is offline 2wice  South Africa
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Quote:
Originally Posted by Hiten View Post
A noob idea.
Can a jig be set up in such a way that the main pivot is fixed, the horizontal line across the vinyl is fixed by a track can be placed on which the jig dummy headshell can be moved. and the ellipse part would have sharp marker; so when we move the dummy headshell across the record it traces the ellipse ?
Regards
I've basically done this digitally to calculate the perpendicular point between the idler and moving cam for every degree of the tonearm arm rotation. It's working on paper so far.
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Old 9th February 2018, 04:56 AM   #1712
nocdplz is offline nocdplz
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Maybe Walter, but I can give you just an answer: try it.
Instead that's why using a rubber belt: a belt has no motion relative to the pulleys. so it does not have friction - on the contrary we need that does not slip with respect to the pulleys, with the least possible tension (load on the bearings). The force dispersed (2- 3%) is only the deformation of the material of the belt (and the more rigid, the worst).
That's how it behaves in the prototype: in respect to the tracking forces (0.1 - 0.2 gr) the belt is completely rigid, the elasticity comes into play only with discs with marked eccentricity, in my opinion softening stresses in a positive way. With a rigid driving system this job should be done by the cantilever, with probable damages.

The problems of these arms - as reported by Doug - are: off-axis loads, inevitably relevant horizontal mass - complex mechanics and consequent frictions - use of ball-bearings.
I add another one: the relationship between side force and stylus drag that moves these Birch based arms varies between external and internal gooves, and I still could not analyze correctly the resulting force. With a normal or a test record the thing is not perceptible, but I am convinced that there are some consequences in tracking.

Hiten: long time ago Doug had done something similar to find the right pattern of the magnetic guide, with Schroeder's approval. Linkage, the program linked by Jcarr seems a great tool to explore geometries.
carlo

Last edited by nocdplz; 9th February 2018 at 05:02 AM.
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Old 10th February 2018, 03:16 AM   #1713
Hiten is offline Hiten  India
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ahh. OK.
Regards.
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Old 19th February 2018, 10:48 PM   #1714
dtut is offline dtut  United States
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So far:
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Old 20th February 2018, 12:09 AM   #1715
berlinta is offline berlinta  Germany
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[QUOTE=nocdplz;5290716]addendum

What I know from previous tests (Schroeder mentioned it as one of the merits of his solution) is that the guide must be elastic, otherwise at the first eccentric LP (do you have one that is not?) goodbye cartridge.

Hi guys,

about the above: not quite... any decoupling(rubber band, magnetic coupling...) in the horizontal plane will lower the eff. mass in the horizontal plane and , when tuned properly, act as an antiresonator, reducing the lateral arn/cart resonance frequency peak substantially. Rigid coupling would not kill you cart upon playing an eccentric record...

Did anyone check out the arm that I took to the Munich High End Show in 2016? Didn't receive much notice, but it proved that there is more than one path leading to Rome, - and it utilizes a rubber belt..:-)

The orientation of the lever is different but the functioning principle is identical to what was discussed here lately.

A video is available here:

Innovator Tone Arm Designer Frank Schroder Explains The Workings of the Rare Neumann Turntable | Analog Planet

All the best,

Frank
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Old 20th February 2018, 04:21 AM   #1716
2wice is offline 2wice  South Africa
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Originally Posted by berlinta View Post
Rigid coupling would not kill you cart upon playing an eccentric record...
Best news I've heard the whole day.
I'd near given up on the Rolamite idea.
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Old 20th February 2018, 08:10 AM   #1717
nocdplz is offline nocdplz
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.... so good, Doug!
I'm glad the rabbits started to grow and multiply, what are your first impressions?

And I'm also glad to discover that I've reinvented the wheel, if it's a Schroeder's wheel: at least I'm sure it's a round wheel. You know what happened with the square one of the Syrinx.
At this point I would like if Frank Schroeder could give us some more information about that arm, because from the linked video does not look like a Birch based (P. forward hor. pivot?)

Rigidity vs elasticity: effectively that statement was melodramatic (I am italian, guys) so after I have always spoken just of possible damages: seing a stylus bending always worries me, and my favorite records detest the skipping. Imho it's the arm that has to deal with the eccentricity, not the cartridge.

carlo
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Old 20th February 2018, 06:54 PM   #1718
dtut is offline dtut  United States
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Rabbits are famous for coupling, not decoupling. Magic rabbits might be different.
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Old 26th February 2018, 01:57 PM   #1719
nocdplz is offline nocdplz
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Hi all - Rabbit tonearm (almost) done.
Working on stiffness and lightness complicated a bit the construction. I gave up with the lifter in order to have a sturdy double crank system (design modified from previous). A small spring counterweight saves about 40 grams, so the total weight of moving masses is below 120 gr, which is an acceptable value for normal tonearms.
The most difficult things to build without a mill are the cranks and the vertical pivot: with my pillar drill I got a 0.12 mm error for the axes distance, and it took me a lot of patience to get there.
Ball bearings now are loaded almost properly, so having 4 instead of 2 does not increase frictions. Now it's easy to set up (leveling, spindle distance, proper angling are all fine tunable) and quite comfortable to place precisely on every trace of the record.
Some experiment are needed for cables that, being exposed on top, must be more resistant than those used on test-Bunny, but still very flexible.

carlo.
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Old 26th February 2018, 06:00 PM   #1720
RCruz is offline RCruz  Switzerland
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[QUOTE=berlinta;5347205]
Quote:
Originally Posted by nocdplz View Post
addendum

Did anyone check out the arm that I took to the Munich High End Show in 2016? Didn't receive much notice, but it proved that there is more than one path leading to Rome, - and it utilizes a rubber belt..:-)

The orientation of the lever is different but the functioning principle is identical to what was discussed here lately.

A video is available here:

Innovator Tone Arm Designer Frank Schroder Explains The Workings of the Rare Neumann Turntable | Analog Planet

All the best,

Frank
Outstanding
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