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Old 30th March 2003, 03:04 AM   #1
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Default DIY Unipivot Project

hello...

ok, so i'm on my way to making my (first) tonearm, and i have a couple of questions i wanted to throw out at all of you.

1) what arm material do you all favor. i am currently leaning towards wood, perhaps ebony (hey, if it works so well in mpingo products...). but i can also easily get various metal tubes (large, or very small diameter? any preferences. i noticed that more often than not unipivots with metal wands opt fot the really thin metal ones) and also ceramic tubes. so i wanted to get some opinions on that.

2) for the pivot cup (upward facing point) i was going to use a sapphire vee-bearing, and i saw this page

http://www.engineeringfindings.com/cat22/cat22pg290.pdf

and what caught my eye were the bearing assemblies (not the ones with the springs, the ones that are simply the vee-bearing mounted into a set screw). besides being easier to work with i feel, i had what i feel is an excellent idea for their application, especially if i do opt for at least part of the tonearm assembly being made of wood (and i think that were i to make the armtube something other than wood, i would make the area that the pivot is attached to out of wood for its sonic signature anyhow). if i were to- at the pivot point of the arm- drill a hole straight through it, and fit it with a brass threaded insert (the knife-threaded types, maybe a dab of titebond in ther too just to make sure it won't go anywhere) then i could simply screw this bearing assembly into that insert, and though i would NOT use this for adjusting VTA, (i will have something else for that) i could then (from the top of the arm, using the screw on the bearing assembly) adjust the height of the pivot relative to the arm so that for different cartridges i would still be able to keep the pivot height in exactly the same plane as the stylus, and also do it rather conveniently. wondered what you all thought???

3) for the pivot itself i was considering using (ala morsiani arms) a gramaphone needle (cheap, easy to find, and available in multiple hardnesses so that too is another easily tweakable feature of this plan) thoughts?

4) also, i had an idea for the couterweight that may be a great idea or not. that's why i'm asking y'all . i like the idea of underhung couterweights, but they of course exert a higher downforce on the cart on warps and the like, so that's no good. Roksan in their artemiz arm use a free swinging counterweight that supposedly minimizes this, and by not being rigidly attached relieves the problem of energy and vibrations in the counterwieght. so what i was wondering if anyone had tried before or had any thoughts on is an underhung counterweight that would be adjustable in its position (in the horizontal plane) to the pivot but hung from a piece of string off of the tonearm. this would, i think relieve the excessive downforce on the cart during upward movements of the arm. i would need to use a rather stiff string so to avoid the couterweight at times of large movement "jerking" the tonearm. at any rate, your thoughts ideas would be appreciated.

5) the only method of anti-skating i have ever seen or could imagine that is at all accurate and acceptable is the use of magnets (again, ala morsiani- see interview on TNT audio), i was wondering if anyone of you had tried this, and how it worked out? of course, this i can worry more about once the arm is up and running i suppose. but i'd like to plan it out now.

6) any general advice you can give me, recommendations, sites to look at would be greatly appreciated. and also any info on how you made YOUR arms, how you acheieved antiskating, azimuth adj. what tonearm wire you used, mouting, etc... and of course pictures of your arms i would love to hear/see, thanks

jesse
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Old 30th March 2003, 10:39 PM   #2
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would a drawing help?
do you see what i'm getting at here?


Dice45 where are you?
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Old 31st March 2003, 08:47 AM   #3
peterr is offline peterr  Netherlands
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Quote:
Dice45 where are you?
Dice is no longer part of the forum. I for one would like hime to come back but i doubt if he will.

Quote:
would a drawing help?
yes.

I suggest you do a search first. There is a lot of info about DIY arms on this forum. I expect you to find most of the answers you require
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Keep an open mind. It helps.
Peter
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Old 31st March 2003, 08:05 PM   #4
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i have searched this entire site and many others regarding this, and these are the questions i'm still left with.
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Old 31st March 2003, 09:47 PM   #5
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Magnets can be made to work effectively, my Decca International unipivot uses them for anti skate. they sit in a sliding collar that increases the force as it moves higher up the arm pillar.

That being said, I think for DIY the implementation might be tricky and I've got to say that the dangling weight on the fine string should work well. (500 arm manufacturers can't be wrong)

Wilson Benesch use this method of A-S in all their unipivot arms.

The story seems to be that you should apply approx 1/4 of the tracking downforce as a sidepull to the tonearm. In effect, if you have a 9 inch arm and you apply a force from a weight that's the same as your downforce (say a 1.5 gram weight) you need to set it up so it's being applied at 2 1/4 inches from the arm pivot.

If you set up the A-S arm so you could adjust the connection point of the string from 3 inches back to 1 inches you ought to have oodles of adjustment.

I'm currently building a diy unipivot myself but work commitments (and building a new phono stage) have got in the way lately.

I hope to be back into it again in the next week or two.

Drew
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