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Old 25th June 2013, 06:59 PM   #551
alighiszem is offline alighiszem  Hungary
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[QUOTE=directdriver;3539059]Exactly. The clever thing is that it never had to use any linear bearing or any contact type of bearing, hence the low friction. The shape of that curved metal is crucial to the tangential accuracy, though.

During play friction pulls the needle forward, i.e. it exerts a turning moment on the brown lever (clockwise). This tries to turn the armwand anticlockwÝse, what is countered by the pulling force of the magnet. As a result the brown lever stays in place and the sum of the forces pulls the needle inward, to the center of the record. I would not call this ideal.
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Old 25th June 2013, 09:06 PM   #552
berlinta is offline berlinta  Germany
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Hi,
I can demo(did that many a time by now) that the arm(when set up properly) will remain stationary once set down on a blank disc(irrespective of VTF!!!)... a mild blow will move it across the disc though(either way).

(@alighiszem):Your analysis is semi-correct, but there is more to the design than what is visible in the pics. Even if what you describe would be all there is, the resulting skating force would maximally be less than 1/3rd of an arm of comparable eff. length(offset angle accordingly).

Is no-one building a clone yet? :-)

The patents cited are mostly based on the Thales circle(one arm features an offset angle). My design doesn't depend on it.
The guide/control mechanisms are all friction laden(or too massive), require an electrical circuit or/and are complicated as hell.

All the best,

Frank
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Old 25th June 2013, 09:11 PM   #553
ecir38 is offline ecir38  United States
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Frank, will you be at RMAF with this arm this year?
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Old 25th June 2013, 09:15 PM   #554
berlinta is offline berlinta  Germany
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Yup, just like the previous two years.... in fact I've not missed a single RMAF yet :-)

Hope to see you there(and other DIYaudio guys as well)!

Best,

Frank
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Old 25th June 2013, 09:19 PM   #555
Joachim Gerhard is offline Joachim Gerhard  Germany
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I registered yesterday.
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Old 25th June 2013, 10:44 PM   #556
directdriver is offline directdriver  United States
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Quote:
Originally Posted by alighiszem View Post
During play friction pulls the needle forward, i.e. it exerts a turning moment on the brown lever (clockwise). This tries to turn the armwand anticlockwÝse, what is countered by the pulling force of the magnet. As a result the brown lever stays in place and the sum of the forces pulls the needle inward, to the center of the record. I would not call this ideal.
The guiding arm that holds the magnet is in line with the main arm and if it's tangent there will be no side force (counterclockwise) to pull away from the skating (clockwise) force (which does exist according to Mark Kelly) which is minuscule. Bear in mind the magnetic guiding arm is not acting as pulling device horizontally, more as a rail like a linear bearing except no contact.... to keep the main arm in the quasi-Thales geometry or close to it.

I believe, as a design, it's a good compromise. Personally, I would take this over anything that involves an air-pump, my pet-peeve!

Oops, I posted the above right after Frank posted his reply. It's best to let the designer do the talk.... so ignore me please.

Last edited by directdriver; 25th June 2013 at 10:47 PM.
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Old 26th June 2013, 02:26 AM   #557
dtut is offline dtut  United States
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Quote Frank, "Is no-one building a clone yet? :-)"

I've tried and thought I was getting close to understanding the main tricky bits, but I hit the limits of what I can machine accurately. I haven't given up, but I put it aside for a while and went on to other projects. If I'm right about this design, I'm in awe of what Frank has accomplished especially considering that the parts that make the alignment work seem to get smaller with each new iteration.

I hope to see the arm and meet Frank at RMAF this year.
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Old 26th June 2013, 05:31 AM   #558
Sprags is offline Sprags  United States
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When is someone going to just invent a device that levitates the cartridge with the stylus oriented in exactly the correct orientation at its continuos path from OD to ID on the LP with nothing actually physically attached to the cartridge?
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Old 26th June 2013, 06:38 AM   #559
directdriver is offline directdriver  United States
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Quote:
Originally Posted by Sprags View Post
When is someone going to just invent a device that levitates the cartridge with the stylus oriented in exactly the correct orientation at its continuous path from OD to ID on the LP with nothing actually physically attached to the cartridge?
By the time you can really do that, will you even play vinyl? I think imaging the vinyl groove is more practical like that laser reading record player but more advanced... or MRI or a super scanner etc...

But I like your idea though.
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Old 26th June 2013, 10:50 AM   #560
Mark Kelly is offline Mark Kelly  Australia
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Quote:
Originally Posted by berlinta View Post
Is no-one building a clone yet? :-)
Frank

I think the few people who are capable of understanding what you have achieved are so in awe of it that thoughts of a clone are anathema. When it became clear how you'd managed the magnetic tracking on the third link I was gobsmacked.

I'm still working on the arm that I call "string theory", it's less elegant than your solution but still fun.

Wish I could make it to RMAF but there's no chance, I have several prototype bicycle frames to build.

All the best

Mark

Last edited by Mark Kelly; 26th June 2013 at 10:53 AM.
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