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Old 25th May 2010, 11:09 PM   #41
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Here's another idea, horizontally it has three pivot points which is a lot and may be difficult to make it work. The idea is to keep the split plane concept like the Dynavector but imagine the arm is extendable just like the one of two lines in the Thales triangle. But the guiding requires moving arm base with a magnet tracking, not touching, a steel rail below to keep the cartridge in tangent.

The red guiding arm is similar to what I proposed earlier with the tuning fork idea. Sorry again for the crude drawing.

Click the image to open in full size.

I am working on another idea that can will reduce the pivots.

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Old 25th May 2010, 11:48 PM   #42
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Hi again!
And thanks for pointing out the thread on the italian forum above. I just like to point out that I wasn't aware of it and had no intention to copy anyone without permission. In fact I got permission from Micha Huber to show that arm. And I had conceived it quite some time ago(together with various other solutions for pivoted linear tracking arms), mainly to combine the positive traits of the RS Labs arm with the zero tracing error offered by the Thales arm. I'll never be a commercial product, only built to find out if the added complexity outweighs the theoretical benefits. Which brings me to the "sound" of this arm.
Extremely tight and well controlled bass, mainly due to an effect that hasn't been discussed here. The arm-cartridge resonance frequency in the horizontal plane is nearly undectable if the thread tension(restoring force), combined with the inertia of the pivoting headshell+cartridge leads to an fres exactly at or near the fres with a fixed headshell. It acts as an anti-resonator.
Since the arm is so short(185mm eff. l.), energy storage/armwand resonances are very low. Image placement and specifity is exemplary. Build one and you'll hear how well it works.
Hope those italian DIYers get to read this as I don't speak or write italian. Don't want them to think I presented myself as the inventor of the Thales principle. Quite the opposite. Micha Huber deserves a lot of praise for his out of the box thinking.

All the best,

Frank
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Old 26th May 2010, 05:18 AM   #43
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Quote:
berlinta:"Which brings me to the "sound" of this arm. Extremely tight and well controlled bass, mainly due to an effect that hasn't been discussed here. The arm-cartridge resonance frequency in the horizontal plane is nearly undectable if the thread tension(restoring force), combined with the inertia of the pivoting headshell+cartridge leads to an fres exactly at or near the fres with a fixed headshell. It acts as an anti-resonator. Since the arm is so short(185mm eff. l.), energy storage/armwand resonances are very low. Image placement and specifity is exemplary. Build one and you'll hear how well it works."
Thanks for sharing your experience, Frank! I forgot to ask how well does it handle warped records since the armtube is so short and there's constant lateral force to the right which I imagine to be stronger than usual for it to guide within the Thales circle. I am looking into my pile of spare arms and parts for a good candidate for this experiment. I imagine an arm with no built in antiskating mechanism would work, like the Audio Technica ATP-12T, which unfortunately I sold last year. I have a Kenwood KD-770D that has a straight armtube with no offset angle that just might work...

I also wonder if unipivot is a good or bad idea for this type of design. Your arm is essentially a unipivot design so I guess it will work. The pivot point of the string will act as stabilizing the unipivot provided the height is matched to the main arm's pivot point.

Speaking of unipivot, I believe the new Thales Simplicity model lends itself to unipivot design since two armtubes in parallel can sit on two unipivot bearings without inherent azimuth rocking and certainly can simplify the design further.

Yes, credit must be given to Michel Huber for thinking outside of the box. I salute him! I believe the Italian forum poster is aware of the designer of the Thales arm and I appreciate him in investigating further into the genre. He's also aware of the contribution of the host, Yosh, of the Japanese website on this topic. I look forward to more ideas on such designs before we have to resort to air pumps and motors!

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Old 26th May 2010, 05:20 AM   #44
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Default pivot headshell porn!

More pictures of rotary headshells from Japan!

More pictures of complicated tonearm from Japan!

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And more pictures rotary SME 3 headshell from Italy!


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Old 26th May 2010, 06:49 AM   #45
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Quote:
Mark Kelly: "Arm design incorporating Burne Jones' Thales circle concept and Dynavector's split planes concept. This design fails for the usual reason: the complexity of the bearings creates excess friction or excess play (or both). Currently working on a new version incorporating a new concept which seems to avoid this problem."
I believe this patent by R.W. Birch can help reducing the number of pivots on the horizontal plane in this "split planes" concept, particularly figure 2.

http://www.freepatentsonline.com/3476394.pdf -- by R.W. Birch 1969

Click the image to open in full size.

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Old 26th May 2010, 07:18 PM   #46
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Quote:
Originally Posted by directdriver View Post
Thanks for sharing your experience, Frank! I forgot to ask how well does it handle warped records since the armtube is so short and there's constant lateral force to the right which I imagine to be stronger than usual for it to guide within the Thales circle. I am looking into my pile of spare arms and parts for a good candidate for this experiment. I imagine an arm with no built in antiskating mechanism would work, like the Audio Technica ATP-12T, which unfortunately I sold last year. I have a Kenwood KD-770D that has a straight armtube with no offset angle that just might work...

I also wonder if unipivot is a good or bad idea for this type of design. Your arm is essentially a unipivot design so I guess it will work. The pivot point of the string will act as stabilizing the unipivot provided the height is matched to the main arm's pivot point.
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Hi again,
Warps appeared to be no problem. After all the arm is still many times longer than, say, a Souther, Revox or (part)Dynavector arm and the actual vertical pivot point is quite close to record level(unlike above mentioned arms)
Unipivots are (almost) as suitable as gimballed arms for the Thales thread assembly. Mainly due to the fact that the thread exerts very little force! The headshell bearing(s) need(s) to be of the highest quality. An additional skating compensation mechanism is beneficial since one can dial in a combination of (positive OR negative!)"conventional" antiskating force and restoring/antiskating force resulting from the hanging weight. Ideally if the hanging weight was chosen to compensate the skating force, the restoring force(the "tangential pull") should suffice too.
BUT!!! (ha, there's no free lunch..:-) all bets are off once the headshell bearing is no longer perpendicular to the record. That's when you need the usually odd(read: clumsy) looking threaded rod/counterweight nose "extensions" to create a neutral balance pivoting headshell. Azimuth HAS to be adjusted by shimming one side of the cart or via a central, raised ridge on the bottom of the headshell(cart screws are just to adjust the tilt).
Changing VTA by raising or lowering the arm bearing is likewise problematic.
For a commercial product, the above spells DESASTER. Thank goodness we're surrounded by likeminded nuts :-)
Wiring is the next problem. After looking at the pictures of the short arm, you can imagine that one doesn't want any "spring" connecting the headshell with the armwand.
Yup, there are easier ways to play a record, they're just not as much fun...

Cheers,

Frank
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Old 26th May 2010, 10:18 PM   #47
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Default string theory

Another idea with string inspired by these string arms.

Let's have a pivot with wingspan above the headshell and two strings going along the armtube and tie to another pivot wingspan right above the horizontal pivot of the arm. Both pivoting wingspans are mounted on the same armtube so VTA is locked to each other and the two strings are tensioned at all times. And part of the wingspan sticks out acting as the guiding arm to force the cartridge close to the Thales circle. This guiding arm has to be slightly lower to match the height of the vertical bearing pivot point so movement can be precise. This can be implemented on arms like a Rega. The advantage of this is to shift most of the mechanism to the bearing area and also low mass. I haven't figured out the geometry yet but that's the gist of it.

Click the image to open in full size.

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Old 26th May 2010, 11:45 PM   #48
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Lovely!



Regards zeoN_Rider
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Old 30th May 2010, 08:32 AM   #49
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Instead of having the rear attachment points on the bearing assembly, would it not be possible to use a 'pair of cams' for the rear string to run around, thereby changing the angle by any amount desired?
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Old 31st May 2010, 03:23 PM   #50
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Default Two Strings or Two Arms

Quote:
zeonrider: "Lovely! . . . "
Sarcasm is not helpful in the experimental spirit. Oh, well...

Quote:
ralphfcooke: "Instead of having the rear attachment points on the bearing assembly, would it not be possible to use a 'pair of cams' for the rear string to run around, thereby changing the angle by any amount desired?"
Thank you for the suggestion. You are right, a cam system should work. I was mainly concern about the vertical geometry because the main arm pivots up and down if any additional horizontal pivots not located at the height of the bearing will affect the vertical movement. My original idea was not well thought out, hence the mocking by Mr. Zeonrider. Hey, no laugh no gain!

After looking at the string system again, I realize there's no need to reinvent the wheel as the mysterious Japanese arm has apparently done all the homework by placing two static pivots around the main arm pivot point matching the same height. Brilliant!

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I guess in spirit the two-wand arm designed by Robert Van Eps is similar, just imagine the two strings are replaced with two wands. It would likely cost more to make. I think this arm would benefit from using a unipivot bearing for each wand and would simplify things. I suppose the Thales Simplicity tonearm fits into this two-wand arm genre.

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Last edited by directdriver; 31st May 2010 at 03:25 PM.
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