Magnetic pull kevlar suspension tonearm

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cressy
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#16 Re: Magnetic pull kevlar suspension tonearm

Post by cressy »

Ah I see what you mean.the bending force applied to the wand by the magnets trying to stay where they while the arm moves adds to the vtf figure
Last edited by cressy on Fri Apr 21, 2017 2:49 pm, edited 1 time in total.
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Nick
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#17 Re: Magnetic pull kevlar suspension tonearm

Post by Nick »

Mind you, if the moving magnet is spherical, the above isnt a problem
Well, the shape may be spherical, but it will still have a north and south pole opposed to each other, otherwise you would have created a monopole and that would be far more interesting than a tonearm :-)
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#18 Re: Magnetic pull kevlar suspension tonearm

Post by cressy »

Spherical magnets would negate the clearance issues,
Would be some breakthrough in particle physics to create a monopole magnet :D
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#19 Re: Magnetic pull kevlar suspension tonearm

Post by shane »

If you break it down to its simplest form, imagine a cylindrical magnet suspended a mm above another one. If the thread is attached to the top of the suspended magnet, then when you try to twist the suspended magnet away from vertical you're increasing the gap, and will have the full force of both magnets opposing you. If the top magnet pivots around a point level with the gap, that doesn't happen.
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#20 Re: Magnetic pull kevlar suspension tonearm

Post by shane »

The first time I tried this, the magnet I used was about 10mm high with a hole down the middle so the pivot point was about 10mm above the gap. This was enough to hold the arm horizontal even without the counterweight fitted. It wasn't a question of slight variations in VTF, the thing was completely unusable!
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#21 Re: Magnetic pull kevlar suspension tonearm

Post by Paul Barker »

so at that, isnt the ideal to have two balls one drilled, but as mentioned tapered so pivot point is bottom? taper needs must be extended right to top of arme so no part of arm can touch thread at any lilely up down movement. Quite a large opening at the top of the arm.

And now, no anti scate provision. which may not matter.

anyway kevlar not arrived and havent yet ordered any magnets.
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#22 Re: Magnetic pull kevlar suspension tonearm

Post by cressy »

If I were building one id use a flat magnet as the fixed one and a spherical one as the one in the wand. Id use a yoke initially as it id want to see if i could drill into the wand magnet first
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#23 Re: Magnetic pull kevlar suspension tonearm

Post by shane »

Which ever way you do it, the pivot point is always oat the point where the thread is held captive.
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#24 Re: Magnetic pull kevlar suspension tonearm

Post by Nick »

Can I just point out that we are now requiring a spherical (or at least half sphere magnet, into which we need to drill a conical hole. The solution is in danger of becoming ore complex than the problem.

Reed (I must try getting a adapter made for my sp10 so I can fit the arm) get around the problem by using a magnet and pin in cup bearing in one plain, and two pin in cup bearings in the other.

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#25 Re: Magnetic pull kevlar suspension tonearm

Post by Ali Tait »

You have a Reed Nick?

Was looking at those the other day, looks a nice bit of kit.
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#26 Re: Magnetic pull kevlar suspension tonearm

Post by Nick »

Well, I have access to one. I don't own it, its never gone back after we borrowed it for a Whittlebury a couple of years agp. The turntable it was with has gone elsewhere (sold), but the arm is sitting on my floor in its wooden box. I need to get around to getting an adapter made so I can try it where the Hadcock normally lives.
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#27 Re: Magnetic pull kevlar suspension tonearm

Post by Paul Barker »

And should this pivot point be same plane as record?
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#28 Re: Magnetic pull kevlar suspension tonearm

Post by shane »

Ideally yes, I suppose, but I don't suppose it matters more with thread suspension than any with other type of bearing.
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#29 Re: Magnetic pull kevlar suspension tonearm

Post by cressy »

Im trying to see if having the pivot point on the same plane as the stylus makes a difference with the unipivot, i think it would be best if it is. Wether it actually is, I dont know yet
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#30 Re: Magnetic pull kevlar suspension tonearm

Post by shane »

Because the vertical movement of the cartridge follows an arc around the pivot, there is a slight fore-and-aft movement of the stylus as it rides over warps, which will cause a slight variation in the speed of the groove relative to the stylus, known as warp-wow. If the arc is exactly vertical where it meets the vinyl on a perfectly flat LP, which happens when the vertical pivot is at record level, then this movement is at a minimum. I can't honestly say that I've ever actually heard any effect from it though, let alone any audible difference between arms with pivots st different levels. It's a very tiny effect. If the warp is bad enough for warp-wow to be audible, it'll probably be the least of your problems!
The world looks so different after learning science. For example, trees are made of air, primarily. When they are burned, they go back to air, and in their flaming heat is released the flaming heat of the Sun which was bound in to convert air into tree.
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