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Old 26th August 2012, 02:32 AM   #11
dtut is offline dtut  United States
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Frank,

Thanks for posting. I should have known somehow this approach would have your fingerprints already on it. Twenty-five years ago? Damn. I'm running the Heim joint dry because of the dust concerns. I had doubts about how low its friction would be, but the one I'm using moves quite freely so I'm going to continue playing with it for a while. There may be ways of burying it in the arm so it's somewhat protected, although that presents its own set of new problems.

And thanks for the description of your magnetic unipivot. I think I've figured out how it might go together and I've got the materials to, at least, build a mockup and then post pictures to see how close I've gotten. At the same time, I can test the reasoning in my response to sreten in #6.

That circular attractor is a great idea.
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Old 27th August 2012, 04:25 AM   #12
bgruhn is offline bgruhn  United States
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Quote:
Originally Posted by dtut View Post
Frank,

Thanks for posting. I should have known somehow this approach would have your fingerprints already on it. Twenty-five years ago? Damn. I'm running the Heim joint dry because of the dust concerns. I had doubts about how low its friction would be, but the one I'm using moves quite freely so I'm going to continue playing with it for a while. There may be ways of burying it in the arm so it's somewhat protected, although that presents its own set of new problems.

And thanks for the description of your magnetic unipivot. I think I've figured out how it might go together and I've got the materials to, at least, build a mockup and then post pictures to see how close I've gotten. At the same time, I can test the reasoning in my response to sreten in #6.

That circular attractor is a great idea.
Hi Doug,
Have you given up on linear trackers/cantus? I built a magnetic unipivot of sorts 3 or 4 years ago based on an upside down Morisiani (sp?) configuration. The needle point pointed up and was attached to the arm wand. A neodymium magnet with a conical seat was located above the arm. magnetic attraction sucked the arm wand and needle upward into the conical seat. Underneath the arm, and part of it was a fluted wire nut which dipped into a small reservoir of silicone fluid (pretty stiff stuff). This was an attempt to make a fluid damped unipivot that didn't float around like the Well Tempered arm with its string suspension. It was a crude device but worked well. Then I got started on a Schroeder clone and dismantled the upside down needle bearing. I'll be publishing pics of a pretty well designed and finished Cantus style arm in the near future. I think that will be my final one for a while. LT seems to be the best for me.
Rgds,
BillG

Last edited by bgruhn; 27th August 2012 at 04:28 AM. Reason: added clarification
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Old 29th August 2012, 10:50 PM   #13
dtut is offline dtut  United States
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Hey Frank,

Did you mean something like this? Is it even close?

Hi Bill,

No I haven't quit the LT adventure. This idea is just goofy enough to grab my attention and I wanted to follow up. I considered something like the magnet attracted upward point, but thought it would scare my wife. Having her feel comfortable using the tone arms I build is a big factor in the design I'm looking forward to your post about the buffed out LT.

I'm going to wind up with three or four TT s each with a different kind of arm - unipivot, LT, vintage conventional pivot, and so on. Different combos, different sounds, but all fun to listen to. I was skeptical about the synergistic claims for TT/tone arm/cart combos, but I learned better and I'm having fun playing with them.
Attached Images
File Type: jpg new mp.jpg (208.4 KB, 253 views)
File Type: jpg new mp 1.jpg (187.2 KB, 249 views)
File Type: jpg new mp 2.jpg (216.5 KB, 242 views)
File Type: jpg new mp 3.jpg (189.0 KB, 233 views)
File Type: jpg new mp 4.jpg (182.7 KB, 230 views)
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Old 29th August 2012, 11:49 PM   #14
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Hi Doug,
Implementation looks a little rough and there are more suitably shaped magnet / circle segment element options, but - essentially, you got it. The way the bottom magnet is positioned, you'll experience a restoring force similar to an antiskating force.... for various reasons.

Good night and good luck!

Frank
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Old 30th August 2012, 03:15 PM   #15
dtut is offline dtut  United States
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Frank,

Thanks again for the suggestion, description, and now the confirmation. This has been fun to figure out and I like the results, scruffy as it is.
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Old 7th May 2013, 11:15 PM   #16
dtut is offline dtut  United States
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Join Date: Feb 2007
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Last Fall, with Frank Schroeder's help, I was able to build a working magnetic damped unipivot. I'd started out using a Heim joint - aka Rose joint or rod end - instead of a unipivot and I wanted to pursue that idea so I combined it with Frank's magnetic damper, which involved moving the damper to the top. The arm actually works - with a high compliance cartridge, it tracks well and makes decent music.

I've wanted to try a wooden arm for quite a while so I decided to combine that idea with the Heim joint pivot. The Heim joint is buried, which I hope will provide dust protection. The wooden arm is heavy enough that it is much happier with a low compliance cartridge - it's loaded with a Shure M3D/N21D. So far the arm is working well, although I think it could use some kind of anti-skate provision.
Attached Images
File Type: jpg heim 2.jpg (194.8 KB, 89 views)
File Type: jpg heim arm.jpg (213.6 KB, 85 views)
File Type: jpg heim back.jpg (186.4 KB, 80 views)
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