Another DIY Tonearm

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Ray P
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#1 Another DIY Tonearm

Post by Ray P »

Another interesting DIY tonearm that I thought might be of interest to you liquorice pizza connoisseurs.

https://www.diyaudio.com/forums/swap-me ... t-arm.html

They also do a full titanium arm, similar but only fully assembled - looks great.
Sorry, I couldn't resist!
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IslandPink
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#2 Re: Another DIY Tonearm

Post by IslandPink »

Nice. It's a very good price and worth it I'm sure.
I am still sceptical about low-slung counterweights, though. They sound slow to my ears and there are reasons why. Maybe Ant can comment. It would be easy enough to change the counterweight, though.

edit : ..... especially since I saw someone selling a Mayware Formula V arm on EBay at £560 ...
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izzy wizzy
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#3 Re: Another DIY Tonearm

Post by izzy wizzy »

IslandPink wrote: Tue Oct 29, 2019 7:35 pm I am still sceptical about low-slung counterweights, though. They sound slow to my ears and there are reasons why. Maybe Ant can comment. It would be easy enough to change the counterweight, though.
Doesn't that put the counterweight at record level? Would have thought there were many tonearms like that. Triplanar for one.
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Ali Tait
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#4 Re: Another DIY Tonearm

Post by Ali Tait »

SME also. Interesting point though Mark, what are the reasons?
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#5 Re: Another DIY Tonearm

Post by Ant »

You want the pivot point at record level not the counterweight. The only reason for an offset counterweight is stability and simple azimuth adjustment. Which makes azimuth very fiddly. Tried it in various designs over the years and found that the lower it is the less quick the arm is to react and recover to warps. It puts the centre of gravity for the assembly lower than the record surface. It seems to make the arm dull sounding if that makes sense.
There are better ways. I had an interesting conversation with Morgan Jones at an Owston meet, we seem to be on the same wavelength when it comes to arm design, he said that the counterweight needs to be very slightly lower than the pivot point, too low and it kills dynamics and I agree.
It soesnt seem to affect gimbal arms in the same way as it does unipivot for some reason, doesn't make a blind bit of difference to a rega arm to have a low slung counterweight other than looking different and costing more. My AT1100 has a lower counterweight, but that also has lower bearings, putting them at record level in line with the stylus and it's the best tracking arm I have in my collection by far.
I think the mission 774 Ali has also has low bearings.
Ime, what is needed for a unipivot is the stylus and pivot in line and the counterweight centre of mass slightly lower by a few mil at most. Too low and the arm does odd things. But it's a challenge to do this and keep the arm stable which is why I used 2 extra weights to balance the last one I did laterally, and used the bias pull position to keep it stable
The mass needs to be in the right place, centred around the pivot to keep the arm nice and reactive
Just my thoughts
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Ali Tait
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#6 Re: Another DIY Tonearm

Post by Ali Tait »

The CW is lower than the arm wand, but about the same level as the pivot point from memory. It’s been a while and all my vinyl gear is in storage.
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Ali Tait
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#7 Re: Another DIY Tonearm

Post by Ali Tait »

Speaking of VFM arms, this looks good value for a 12” arm-

https://www.acoustand.co.uk/collections ... ew-product
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Nick
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#8 Re: Another DIY Tonearm

Post by Nick »

It soesnt seem to affect gimbal arms in the same way as it does unipivot for some reason
Assuming that's not being sarcastic, I would have thought it was obvious as gimbals only have two axis they can move on, unipivets have three.
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#9 Re: Another DIY Tonearm

Post by Ant »

What I mean is that all things being equal, I. E that both types of arm are adjusted properly and the azimuth is correct on the unipivot, there still seems to be a difference having the too far underslung cw with the unipivot but none with the gimbal. When riding warps they behave the same but the up is dulled down. This was quite marked with the last one I did, it was worse with a lenco counterweight than it was with the one I made which was the same weight and almost exactly the same dimensions, but the hole in the centre and the stub 1/4" lower than the wand
Just what I found, doesn't mean it's the same for all
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Nick
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#10 Re: Another DIY Tonearm

Post by Nick »

But just thinking about warps. Because a unipivot has the extra "twisting" freedom, and because the stylus tip is not inline with the arm because of the offset, the effect of a warp will be converted into a twisting motion, unlike a gimble where the arm can only move up or down. I would expect the position of the counter weight would have some effect in these situations as the arm twist will convert to moving the weight.
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#11 Re: Another DIY Tonearm

Post by Ant »

Well that's the thing with the last one I did, because when I looked at the ways to implement bias I decided to put the outrigger for the bias weight on the left like a hadcock. It is on centre with the pivot, so bias pull doesn't affect azimuth and the loop the bias weight wire runs in and drops down through is also at the same height as the pivot. This means that the twisting motion is also resisted by the bias weight
It it leans to the left the outrigger goes down, or right it goes up meaning that either way the arm has to pull the bias weight up in order to twist. This makes the design very stable and it behaves closer to a gimbal in the third plane. Obviously it can move in that plane, but compared to the formula 4 on the jbe it moves much less in that plane
Even so, the low counterweight made a difference that I didn't like which given the extra stability I built into it makes me wonder if there is something else going on aswell
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#12 Re: Another DIY Tonearm

Post by IslandPink »

Nick wrote: Wed Oct 30, 2019 3:43 pm But just thinking about warps. Because a unipivot has the extra "twisting" freedom, and because the stylus tip is not inline with the arm because of the offset, the effect of a warp will be converted into a twisting motion, unlike a gimble where the arm can only move up or down. I would expect the position of the counter weight would have some effect in these situations as the arm twist will convert to moving the weight.
Exactly, i haven't had much opportunity to post, but this is the nub of the issue, the torsion effects on the arm wand, especially in the bass, can interact with the offset counterweight, on a unipivot. On a gimballed arm, the torsion cannot really get through to the counterweight. I first came across this in a slightly different context on Vic's air-bearing arm when he had a very 'dangling cylinder' weight which was resonating with the thin carbon-fibre wand he used.
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