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Old 17th April 2010, 05:42 PM   #31
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Directdriver: it is my understanding from those who I have spoken with who have hands on experience with Cantus that the roller bearing assembly has superb contact with the surface of the glass track and the bearings are considered to be rigid except for their horizontal rolling motion. The bearing race assemblies in the roller bearings have been designed to have a small amount of slack (self damped by lubricant and sealed) which permits the arm enough motion to track record warps. It is this rigidity which accounts for the arms tremendous control and dynamics. The intent is to transfer as much energy from the cartridge (tip motion in the record groove) into electrical energy as is possible. This is achieved by reducing physical motion in the arm to a minimum.
I had though along similar lines to your possible suggestion of the roller on a knife edge. I had envisioned two captive single ball in cup bearings one at either end of a sled assembly that holds the arm. These would be very small and provide both horizontal motion as well as a pivotal axis point for arm motion, a rolling knife edge bearing if you like.
I discussed this with Bo himself and found his comments to be very interesting. Bo told me that as soon as the arm was allowed to freely pivot to provide forward and backward motion to track warps you have also allowed it to resonate at some frequency. You are then loosing energy and adding distortion through that motion. The purpose designed slack which permits the race assembly to move as a whole so the arm can navigate small record warps and which is damped is all that is required to play through a warp while maintaining the concept of keeping the assembly as rigid as possible. Tremendous bass control and dynamics are two of the primary characteristic qualities that owners of the Cantus repeatedly comment on regarding its performance.
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Old 17th April 2010, 06:28 PM   #32
bappe is offline bappe  Sweden
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Quote:
Originally Posted by directdriver View Post
......My concern with the Cantus arm is that the two rollers are cylindrical and seating on a glass tube would create too much contact points, at least four......
Just want to point out that there is an edge on the bearings so there are only two contact points.

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Old 17th April 2010, 08:38 PM   #33
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Default Cantus arm

As far as I know early versions did have a ridge on the side edge of the roller bearings upon which the arm could pivot but this is not any longer part of the design on current Cantus arms as the rocking action was not considered desirable. The new version is said to be more stable and perform better as a result. The attached drawing shows the old style bearing assembly. Regards.
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File Type: jpg Opus 3 Cantus Bearing.jpg (21.2 KB, 979 views)
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Old 17th April 2010, 11:55 PM   #34
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Thanks to Moray and Bappe for clarifying things and providing more design details. Now that I saw the drawing, it makes sense to have a flange bearing using the ridge as a rolling knife edge to reduce contact area. Judging from previous pictures I was confuse about that and thought the two ball bearings were flat circumference cylindrical shape that would create too much contact area and, hence, friction. This early version is really not much different conceptually from a V-groove bearing riding on a blade or the reverse, a rolling blade riding on a v-groove track. I am curious about the current version if, as you said, it eliminates the ridge and how it behaves vertically. If having more contact area is a good thing then a U-groove bearing riding on a round shaft would help stability, right? This is a fascinating design and its simplicity makes it very DIY-able for this community. Thanks again for the drawing.

By the way, the tonearm on the obscenely expensive Clearaudio Statement turntable uses, I believe, similar concept. Except the armwand is above the bearings whereas the Cantus is below the bearings. Check pictures and websites.

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Click the image to open in full size.
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Click the image to open in full size.

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Old 18th April 2010, 02:00 AM   #35
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Directdriver: perhaps you can re read post # 31. The roller bearings in the current version of the Cantus are designs to permit the internal bearing race a small amount of controlled motion. The bearing race can move within the roller assembly without disturbing the horizontal motion of the sled or carriage.
Here is a Quote from Bo Hansson outlining the design goals of the Cantus

"There are of course a lot of different ways to make a tonearm. My goal for Cantus is in short:

The cartridge tip shall read the information in the track, on the same spot as it was cut, This is not possible with a pivoted tonearm.

The cartridge shall have a stable reference and not be able to "swing" i.e. there shall not be a fundamental resonance in the system. This is not possible with a pivoted arm. To solve this there are two contact points, which make the carriage hold the cartridge so it can move side ways but not get into resonance.

There shall not be resonators coupled to the cartridge, such as the "organ-pipe" resonance that is common with most existing tonearms. I mean that when you have a tube almost one foot long coupled to the cartridge, the tube itself resonates on two foot and four foot tones approximately 300Hz and 600 Hz and overtones of this. By making the tonearm tubes very short, the resonance is forced up to higher frequencies, and by using a very small diameter for the tubes the resonance is further reduced significantly. You can easily hear a tonearm resonance when you put down the cartridge in a quite track on the record. When you compare the sound from Cantus with most of other tonearms you will find Cantus playing the empty track, much quieter than other arms.

There shall not be any kind of energy storage in the system (flexible materials). All mechanical energy shall be converted to electric output from the cartridge.

The vertical movement of the arm riding the record, shall be damped. In Cantus damping is provided by using ball bearings with a little side ways play. This means the contact point in the bearing is changed when the tonearm moves up and down. As the contact point is changed there is automatically a damping, because it's not a resonant point. This is perhaps difficult to understand, so please give it some time and thought." End Quote.
I hope this helps to make it clearer how the arm works.
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Old 18th April 2010, 02:28 AM   #36
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Please note that I was in error about the bearing assemblies in this arm. I had been under the mistaken impression the bearings were lubricated with a light grease this is NOT the case, the Bearings are clean with no lubricant and are sealed. I apologize for this error and thank my dear friend Peter at Pentacone for correcting me
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Old 19th April 2010, 08:58 PM   #37
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Here's one that uses V-groove bearing riding on a string, much like the Clearaudio Tangent.

Click the image to open in full size.

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Here's a rather rare one, Nottingham Paragon linear tracker. Rather elegant looking.

Click the image to open in full size.


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Old 19th April 2010, 10:14 PM   #38
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The Nottingham Paragon looks very nice but the picture does not show much of the mechanical detail did you find any other pictures of it? The first arm shows that even one tensioned thread can support a linear arm. This arm will have a resonance as it allows the arm to freely swing up and down on the V-groove rollers which is something the Cantus eliminates. Thanks for posting these interesting pictures.
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Old 19th April 2010, 11:01 PM   #39
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Here are few more images on the Paragon tonearm. It's really rare. Judging by the look of it, it's essentially two V-groove bearings moving laterally with a short armwand.

Click the image to open in full size.

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Click the image to open in full size.

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Here's one using linear motion bushing made by THK for horizontal movement. More pictures in the website and I believe the DIYer can reduce the mass even further if he simply glue the armwand directly below the bushing without using a coupler.

Click the image to open in full size.

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Click the image to open in full size.



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Old 19th April 2010, 11:24 PM   #40
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can't get either of your first two images to open? can you reference the page you found the pictures on?
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