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Old 27th February 2016, 08:15 PM   #1
paulfk is offline paulfk  United Kingdom
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Default Linear tracking arm in liquid

Hi all, having read several threads about linear trackers and seen the DIY efforts of many dedicated members here of the glass tube variety, ala clearaudio etc got me thinking. I don't like the ball bearing inside or outside a glass or metal tube/round bar idea as it seems to me unlikely a ball bearing will rotate without sufficient weight as the friction within the bearing will prevent this and it may slide first. Now I don't want this to dominate this thread and it's only my thoughts and may have no foundation. It's just made me think would it be possible to have a tube with the slot at the top with the carriage floating inside on some form of liquid, either water or thin oil etc. Like a well tempered arm but linear. Has it been done?
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Old 27th February 2016, 09:30 PM   #2
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the most popular method has been using compressed air but yes fluids have been used. The trouble with all of these designs is that they miss the benefit that mechanical systems provide which is damping of arm assembly motion to prevent resonance. If you watch any of the numerous you tube videos of mechanical bearing assemblies you will find that when set up properly they roll very effectively. Remember that the bearings are run dry of lubricants which are not necessary or desirable at the speed of rotation involved and they only create drag. The fact that the arm and carriage have to be dragged up the inside wall of the glass tube as in the Opus3 Cantus is a plus not a negative as the arm has enough damped motion to accommodate normal record surface variations but should a bad warp come along you can still track the warp and not have you arm go into uncontrolled resonance. The less easily your are can move away from where it needs to be the better for energy transfer. That why Bo's design is so very clever, it moves freely right to left and is damped during any up and down motion especially so with severe warps. gravity is enlisted to pull the carriage assembly back down to its correct position after a warp has passed. This aspect of Bo's design is missed by many who simply do not understand what is happening. Yes you can play much more severely warped records when the arm is allowed free swing up and down but that simply degrades performance and severely warped records will never sound good even it you can track them. remember that Bo and Opus 3 were the first to impost and sell the Souther linear tracking arm into Europe. Bo saw this short coming in Lou's design and asked Lou to address it. Lou felt the arm was fine as it was and suggest that Bo design his own and see if it was an improvement. Not long after the Cantus was born and Bo stopped selling the Souther arm.
the only way that you will know for sure is to build both designs and compare. I suppose that you could compare Bo's design to an air bearing to see how they differ. trouble with a free floating carriage in a liquid trough will be unrestricted motion of the carriage in all sorts of directions and you have no way to damp them even when using a keel of some sort a viscous fluid will be required and then you add a huge amount of friction. Why don't you give it a try and see what you discover?
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Old 27th February 2016, 10:11 PM   #3
paulfk is offline paulfk  United Kingdom
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Thanks mj, I will look into it.
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Old 27th February 2016, 10:26 PM   #4
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Done, by Mr. Grimm. Very good job, methinks.

The solid universe: Vinyl audio: DIY linear tonearm

and his video:

https://www.youtube.com/watch?v=q4hK...ature=youtu.be

Very interesting.
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Old 27th February 2016, 11:15 PM   #5
paulfk is offline paulfk  United Kingdom
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Mmm yes, I've seen that before, but while watching the video there was another more interesting arm Orpheus designer, or desinger as it was spelt. On an sp10, now that I would like to know more about. Couldn't anything searching online. I must sign or register on you tube to contact the person responsible for the video.
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Old 28th February 2016, 08:44 AM   #6
paulfk is offline paulfk  United Kingdom
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link to the tonearm on youtube
https://www.youtube.com/watch?v=-WPDKXlQL9I

seems its an air bearing but can only guess as to how its done
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Old 28th February 2016, 08:57 AM   #7
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GoodSoundClub - Romy the Cat's Audio Site - Here is my new tonearm.
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Old 28th February 2016, 09:01 AM   #8
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Quote:
Originally Posted by paulfk View Post
link to the tonearm on youtube
https://www.youtube.com/watch?v=-WPDKXlQL9I

seems its an air bearing but can only guess as to how its done
the captive air bearing is to the right in the metal block and the tube which the tonearm is attached to slides in the air bearing.
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Old 28th February 2016, 09:45 AM   #9
paulfk is offline paulfk  United Kingdom
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Quote:
Originally Posted by moray james View Post
the captive air bearing is to the right in the metal block and the tube which the tonearm is attached to slides in the air bearing.
I guessed that much. looks like a difficult engineering job. I assume the air holes are all around the shaft to stop it from being pushed up and scraping on the top of the housing. I am thinking instead of an air bearing, linear bearings and a hollow shaft, I will go to my local bearing supplies and talk to them, the bearings would need to be unsealed and dry. I was thinking to build one with linear bearings before but with the carriage fixed to the linear bearing but this way looks more user friendly if it works well enough and retracts away from the record without the need to move the whole carriage.
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Old 28th February 2016, 03:05 PM   #10
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Quote:
Originally Posted by paulfk View Post
I guessed that much. looks like a difficult engineering job. I assume the air holes are all around the shaft to stop it from being pushed up and scraping on the top of the housing. I am thinking instead of an air bearing, linear bearings and a hollow shaft, I will go to my local bearing supplies and talk to them, the bearings would need to be unsealed and dry. I was thinking to build one with linear bearings before but with the carriage fixed to the linear bearing but this way looks more user friendly if it works well enough and retracts away from the record without the need to move the whole carriage.
This seems like a 13 mm New Way air bearing. It is about $200 each in the States. However, the design in the video is not well implemented.

Last edited by super10018; 28th February 2016 at 03:08 PM.
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