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Simple wood tonearm with magnetic bearing
Simple wood tonearm with magnetic bearing
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Old 13th January 2018, 04:47 AM   #11
pixworld is offline pixworld  Sweden
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Location: Sweden
Default Well tempered

Quote:
Originally Posted by Rodeodave View Post
The Well Tempered Lab tonearms have antiskating implemented by twisting the suspension thread, maybe pixworld has done the same.

Very nice build!
Thank you for your kind words.
This arm was just a first prototype where I admitted the antiskate funktionality. Partly because I am not sure if its needed on this straight arm with very little overhang, and partly because I know this would be the leas difficult feature to add afterwards if changing my mind.

Yes, I am aware of that Well tenepred used the wire twisting to get the antiskating force. However if the wires are twisted all together (more that 180 deree of twisting) the force will be very low. And if the twisting is less than 180 degree (with separate starting points) the force will change between the outer resectively inner record groove. Meaning the antiskating will be hard to contoll.

Here are a picture showing the wire topp assembly point. Actually the wires meet in a small teflon tube before entering the topp nut to avoid getting teared down.

Click the image to open in full size.
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Old 13th January 2018, 05:31 AM   #12
Cold Beer is offline Cold Beer  Croatia
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Quote:
Originally Posted by pixworld View Post
... Partly because I am not sure if its needed on this straight arm with very little overhang, ...
I am using my 14 inch armtube on my Morch tonearm. Antiskating IS needed, believe me

Click the image to open in full size.
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Old 13th January 2018, 06:04 AM   #13
pixworld is offline pixworld  Sweden
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Default Magnetic bearing

Quote:
Originally Posted by Bare View Post
Very nice craftsmanship in that project.
Bit confused re the Magnetics though.
Seems like the mags simply centralize the arm while the Y (?) shaped wires (?) fitted into those inset brass tubes act as the actual bearing/ pivots.
Can't see what keeps the Two mags from eagerly sliding away / repelling/ / escaping each others magnetic field as fast as possible .
Or am I missreading ?
Thanks for your kind words

This concern were also mine when I started this project, and thats why I sattled to start off and make this simple prototype in simple woods and cheap materials. I wanted to try how stable this arm was in horisontal movements, with only a vertical force to count. Actually the result where very positive.

However, first I must write some words about my thoughts about mechanical plays.

The imaginay picture of a ideal tonearm bearing is an arm where we kan feel no play whatsoever. We whant it leghtwise stiff, not to smear out the sound and loose impulse and signal risetime.
But as a start, ALL bearings has mechanical plays. And the best ball bearing types has plays in the um (micrometer)-region, which is acyally in the same region as the record groove. So "feeling" if a bearing has a play or not is irelevant. By saying that I think it´s more ineresting to go deeper and figure out how different mechanical play look like.

A ball bearing play is often very small, but has a free movement with hard ends. To exagurate this a bit, one kan say that its a free um movement that bangs into hard stopps.
This magnetic bearing play is for certain WAY bigger than the ball bearing. but it has no stiff ends, so it will behaive diffenently. The movement is more or less sinusodial giving less upper resonance fenomina.
So we can choose a ball bearing that feels stiff in bigger regions, but actually has a "bad" type of play in the smaller regions, or a bearing feeling loose in the bigger regions, but has a "kind" play in the smaller regions.
The upper region play (the one we can feel by hand) must by any means be in controll. In a ball bearing this is controlled by its mechanical tolerances, while in this magnetic bearing rely on the arm mass.

Finally I would like to explain how "stiff" or horisontally stable the arm is but its difficult to explain this in text.
But going into a more technical discussion I must first point something out.

At first I just had the two flat magnets facing eachother (not a spheric upper surface as in the picture) making a vertical force. Since the facing surfaces where identical in size, the magnetic force where equally spread all over this surfaces. Any pulling force in the arm trying to get the magnets out of position where held back by an oposite force. This would talk for flat surfaces with sharp ends.

Later on I added a spherical iron hat on the top magnet that can bee seen in the picture. This partly contradict what I just said, but where nessesary to keep a constant airgap when the arm moves up and down.
I am sure that in the optimization between horisontal stiffnes (identical magnetic faces) and constant airgap (sperical faces) is where work shall be done to get this optimal working.
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Old 13th January 2018, 06:12 AM   #14
pixworld is offline pixworld  Sweden
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Default Thoughtful text

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Originally Posted by rickmcinnis View Post
With admiration for the quality of the build I, too, find calling this a magnetic bearing a little presumptuous.

My first thought would be for the builder to experiment with more than two strings for the bearing like Pete Riggle does. I am using his arm and know that very fine sound is available from this approach. His arm is fully suspended from the top with what might be considered a less elegant way to stabilize the arm than the magnets. Unless as stated above the magnets are not absolutely attracted to each other in a line and you end up having to add something to keep them in check. If that is not the case you end up having to do something like Pete did and if you have to stabilize the magnets then you might as well do without it.

The more I think about it it would seem a very long wand would be required to minimize the upper magnet's displacement when making vertical movements? And would the change in attraction have some kind of effect on the stiffness of the bearing? It would introduce a change. Of course, a purely suspended arm would have a comparatively always "loose" bearing. AS I think about it if the two magnets do stay reasonably in line with each other at all times this has to be something worth trying. For all I know it is a concept as old as tonearms!!!

As i argue with myself I keep in mind: Compromise is the one thing we can be sure of. All that matters is which approach produces a sound we can easily convince ourselves has something to do with music in our systems. Sure would be nice if there was the one perfect way.

Not feeling able to make a good arm i went with Pete's. I could afford it and had the adjustability I wanted. Wish I could make my own arm! With Pete I enjoyed doing business with an audio craftsman.

Great admiration for this project.
Thanks for your kind words

You are absolutelly right. Its all about making the compromize as small as possible. But still there are always compromizes. Nothing is perfect
I will Look into Peters design and see if there are something I could adopt into mine
Best regards
Lars
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Old 13th January 2018, 06:16 AM   #15
pixworld is offline pixworld  Sweden
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Quote:
Originally Posted by Cold Beer View Post
I am using my 14 inch armtube on my Morch tonearm. Antiskating IS needed, believe me

Click the image to open in full size.

I have just designed an azimuth-in the fly adjustment on my arm which in my head seemed to have a higher prioritize. Next is a VTA-adjustment and then I will propably ad an antiskate force to the arm
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Old 13th January 2018, 06:27 AM   #16
pixworld is offline pixworld  Sweden
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Default Added a on the fly azimuth-adjustment feature to the design

One of the goals with this projekt was to have a simple on the fly azimuth-adjustment on the arm.
This picture shows the idea
Click the image to open in full size.

When leveler is moved sideways the wire attachement moves making the arm to rotate
Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

I put a small film on facebook where you can see how it works:
Azimuth-adjustment
ETF European Triode Festival Public Group | Facebook

Airgap-adjustment
ETF European Triode Festival Public Group | Facebook
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Old 13th January 2018, 08:23 AM   #17
Cold Beer is offline Cold Beer  Croatia
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Very cool azimuth adjustment!
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Old 6th February 2018, 10:53 AM   #18
ChrisG139 is offline ChrisG139  United Kingdom
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Default Magnets

Hi
Could you give me details on the magnets used?
Thanks
Chris
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Old 6th February 2018, 12:10 PM   #19
jls001 is offline jls001  India
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Really cool arm lifter.

Assuming the four Kevlar threads are installed without any pre-tension, a small twist in the top "knurled" knob ought to provide enough, if fiddly, anti skate adjustment. Of course things are much easier when using a single thread (a la Schroeder)
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Old 6th February 2018, 02:22 PM   #20
ChrisG139 is offline ChrisG139  United Kingdom
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Default Thread Arrangement

Hi Folks
If you look at earlier Schroeder arms, he too had the same arragement prior to opting for the single thread.
Regards
Chris
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