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Old 30th June 2013, 11:04 PM   #11
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Haha, not many into linear arms huh?. The more I listen the more I'm amazed just how good vinyl really can sound. You might also notice the rubber o rings at each end of the glass tube, these are to prevent ringing and act as damping for the glass tube and threaded rod . Dynamics are fabulous, and detail is spot on and speedy which tells me the arm does a fine job of dissipating stored energy quickly rather than slowly sending it back and smearing the sonics.
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Old 1st July 2013, 12:23 AM   #12
AuroraB is offline AuroraB  Norway
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Very interesting execution of an intricate problem.....
Which bearings do you use...?
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Old 1st July 2013, 01:47 AM   #13
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Hi auroraB,

The friction is very low, this was visually tested with some very off center pressings in which the arm will rock back and forth without skewing the stylus . The bearings used are pretty common RC car bearings, 5x9mm with a 5mm center.


Colin
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Old 1st July 2013, 01:55 AM   #14
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Colin if you look you will find that Bo's first arm was a rolling knife edge bearing which provided the same motion your arm does. Later Bo removed the edge from his arm so the rocking motion was eliminated to make the coupling more rigid. If the cartridge was forced to play a bad warp then the arm could simply push the carriage assembly up the wall of the tube and gravity would pull it back down after. In Bo's opinion there is no point building an arm to play badly warped records. Really nice work by the way. Thanks for posting. Best regards Moray James.
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Old 1st July 2013, 02:33 AM   #15
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Many thanks Moray,


The opus if I'm correct?, originally used knife edge bearings then switched to flat bearings?. This arm is almost an inverted opus, instead of riding in a tube it rides the outside of a smaller tube for much the same movement except the balance and weight of the arm itself will pull it up the tube. They both work out to 4 pivot points, but as with the joy of this stuff there was no point just copying an arm.


Colin
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Old 1st July 2013, 08:15 AM   #16
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Did some more work and replaced the nuts as counterweights with a polycarbonate block that slings the weight a little lower, the cow weighs just over 4g.
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Old 1st July 2013, 03:53 PM   #17
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I love linear tonearms and I replaced my VPI 10.5i arm with the Terminator linear air bearing and never looked back!

can you tell me why you decide to not use air instead?
I see pros and cons of using air, but honestly I see more pros.

I would be interested to know your take on that.
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Old 1st July 2013, 04:40 PM   #18
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Quote:
Originally Posted by vynuhl.addict View Post
Many thanks Moray,


The opus if I'm correct?, originally used knife edge bearings then switched to flat bearings?. This arm is almost an inverted opus, instead of riding in a tube it rides the outside of a smaller tube for much the same movement except the balance and weight of the arm itself will pull it up the tube. They both work out to 4 pivot points, but as with the joy of this stuff there was no point just copying an arm.


Colin
Collin here is a drawing of what Bo's bearing looked like originally I see this as a rolling knife edge. As I mentioned the edge was later remover to eliminate the rocking action of the assembly. From discussions with Bo I know that he felt this was a significant improvement with respect to performance. It is nice to find out why changes like this were made. I agree that it is also nice to roll your own. Being able to stand on the shoulders of those who have gone before is very helpful and can make clear the way to new insights into improved and better designs. Again excellent work on your arm I am sure that it will inspire others to give diy a try. Best regards Moray James.

Please Note: the attached thumbnail is a red line drawing on a black background so it looks all black. If you click on the box you will be able to see the drawing without problem.
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Old 1st July 2013, 07:47 PM   #19
Khom is offline Khom  Belarus
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Quote:
Originally Posted by vynuhl.addict View Post
Hi auroraB,

The friction is very low, this was visually tested with some very off center pressings in which the arm will rock back and forth without skewing the stylus . The bearings used are pretty common RC car bearings, 5x9mm with a 5mm center.


Colin
Hi, Colin.
Did you think about ceramic ball bearings? They have very small friction and should works better.
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Old 1st July 2013, 08:46 PM   #20
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Hi Moray,


Those knife edge bearings look like flanged bearings, also available from hobby shops . I took a lot of inspiration looking at different arms on the web and must admit the Cantus was one of my favorite commercial designs because it was simple and worked, very well at that too.


Stephanoo,

I thought about air bearing, but as well as they may work there is a lot of complexity, and I've read mixed views on air bearings, so I decided if anything a mechanical arm was more feasible for a first attempt.


Khom,


I've looked into ceramic bearing assembly's, there may be a small gain in this case, but from what I've been told by some local bearing companies any gain may be small for the expense vs steel bearings, but the way I've used the bearings also keeps friction low since they roll free on a brass shim.


Colin
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