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Sideways Uni-Pivot Arm, SUPATRAC Blackbird, formerly "Ekos Killer (Price?)"

'bout perfect for me, in terms of reading the text alone.

i had a bad feeling you were going to say the maths was straight-forward ... :D
 
Well, we tend to recognise whole words so number of words is the first approximation. If we split the quote at the spaces we get number of words. But we are slower to digest longer words so we can adjust for that by multiplying by the number of letters. But we have factored in the length twice now, so take the square root or thereabouts to get back to a linear relationship with length. Multiply by some factor for human compatibility. Add a couple of seconds to cover start up speed.

No A-level maths required!
 
Hi , can i ask about the pivit , i can see a v shape threaded screw to a point , does the box that carries the weight have a cup for the threaded screw , and
if not does it mean that the point can move on a flat surface , also have you tried other materials there ball bearing for example or delrin , phil.
 
Hi , can i ask about the pivit , i can see a v shape threaded screw to a point , does the box that carries the weight have a cup for the threaded screw , and
if not does it mean that the point can move on a flat surface , also have you tried other materials there ball bearing for example or delrin , phil.

Hi Phil - great questions. The flat surface (the arm's thrust surface made from steel box - hence 'thrust box') can indeed move against the point. However, during playback when the arm is correctly configured there should be almost no movement as the arm swings across the record, and effectively none from one second to the next. This is because the majority of the forces from the cartridge are along the arm, pulling the thrust box directly against the point. The cartridge supplies little torque, so it has inadequate force to scrub the thrust box sideways against the point.

The hardness of the point and thrust surface mean that 'give' in the time axis is minimal and ensures longevity. I assume Delrin is not as hard wearing as steel and HSS.

A ball bearing would not ground the arm as effectively as it would be more likely to react sideways, and it would also recess as the arm advanced across the record, i.e. the contact point will shift around the ball moving the effective pivot position, possibly causing lateral slipping.

A cup makes configuration harder because you need contact to occur at the centre where the point axis is close to normal to the thrust surface. Since the pivot contact always occurs at a single point, a cup serves no useful purpose except making misconfiguration highly likely. On the 100 page LencoHeaven discussion a DIY arm maker has confirmed that removing a cup from his second SUPA design brought a significant improvement in performance. A flat surface allows you to concentrate on positioning the pivot contact exactly on thr line between the hoists' lower flex points, which is critical to the optimal function of the bearing. The idea of a cup is instinctively attractive, and I milled a dimple into the thrust surface of my first prototype but I soon realised that it achieved nothing but a likelihood of misconfiguration.

I find it quite hard to describe the physics of the SUPA bearing design, so if something's still unclear, please don't hesitate to ask.
 
Thanks for your explanation , if you were to put a straight edge down the tonearm lined up with the pivit screw , you would set the post cartridge in the middle of the lp , start and end of lp would be offset , on each side of pivit tip , all the best with the project . phil.
 
Thanks for your explanation , if you were to put a straight edge down the tonearm lined up with the pivit screw , you would set the post cartridge in the middle of the lp , start and end of lp would be offset , on each side of pivit tip , all the best with the project . phil.

This is precisely how it works. To test if the theory works for you in practice, hold a ballpoint pen at 80⁰ to your desk and push it straight down into the desk. Does it slip? Does it make any progress into a hard desktop? Now lean it over to 100⁰ and try it again. Does it behave any differently?

The fact that the pivot point is offset by 10⁰ or more as it presses against the thrust box has no important effect. It will not slide significantly sideways because there is friction enough and nearly all the forces press it straight into the hard surface.

In my experience it still works well if the offset to the normal vector is 0⁰ - 20⁰ instead of -10⁰ - +10⁰.

Why waste resources on a bearing which can turn through 360⁰ when a record only needs 20⁰ of arm swing?
 
I had a good query on another forum which I thought might be worth sharing here, so here it is with my response.

Hi SUPATRAC - would you be able to post a close up picture of your string solution please? Thanks

Sure, here are some pictures of two ways to attach a cuing tress to my dusty, fallow, but mechanically superb Ekos 2. You can see that the tress can be bent over while the record is playing so that it doesn't interfere with any lid, and you can also see in picture 7 why I think this is a good way to avoid excessive downwards pressure on a cartridge. In the penultimate picture you can see that I turned the hoop of a slip knot into a double loop to improve its grip on the arm tube. Obviously there are many knots and many ways to do this to any arm, and the length and flexibility of the string can be selected to taste. I like to put a bit of heat-shrink on the tress to make grip a bit easier to sense, as well as obstructing fray. If your eyes aren't perfect, why not use red heat shrink or funky string?

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When it comes to use, I recommend holding the tress near the end for maximum flexibility and gentleness. If the tress is the right flexibility and length you really can hold it while the record is playing which means you can...

- ensure it's engaged with the groove at the beginning,
- get a sure grip before lifting at the end,
- bend down the tress before lowering the lid,
- grip it between thumb and forefinger with your palm facing downwards, left hand or right which can be a great deal more comfortable than the usual contortions.

HTH.
 
News
I'm working on the final two replacement magnetic pivot arms.

I'm also working on a batch of 180 arms of various lengths - I don't know if that qualifies as 'production'.

From now on arm tubes, pillars and bases are painted with Cerakote.

The manual will soon be updated to describe a new tuning technique and more types of base.

There have been improvements to counterweights, mass adaptors, connector plugs, resonance damping, the bias rig, arm cables, the Supatractor. Mostly improvements are in ease of manufacture and marginal usability - they do not constitute anything like a new version, as the design remains essentially the same.

I'm planning to have a stall at the UK Hifi Show with several turntables and headphones so that visitors can listen to a Blackbird in action.

"The Point Of Music" is now a UK registered trademark of SUPATRAC.

If you have any questions, please don't hesitate to ask.
 
Wonder how this performs with a click that keeps you in the same groove? I’ve an occasional record I play regularly that needs a lift/nudge. Direct contact with the arm tends to overdo it.
 
Wonder how this performs with a click that keeps you in the same groove? I’ve an occasional record I play regularly that needs a lift/nudge. Direct contact with the arm tends to overdo it.

With a record which is damaged or mastered in such a way that an infinite loop occurs even when bias is appropriate, a temporary fix is to blow on the side of the arm with increasing strength until it advances.

I started a thread on the Steve Hoffman forum about my experiences in permanently fixing records damaged or pressed with this type of fault:
https://forums.stevehoffman.tv/threads/mending-records-which-jump.1145659/

Briefly, I have found that with a cheap microscope it is not difficult by hand to fix permanently grooves which suffer from this kind of deformation. My technique is described in the thread linked above.
 
interesting - simply on aesthetic grounds I think it's one of the best looking arms I've seen, particularly in situ.

that is, however, without the dangly, cage-like thingies mid-arm, important as they are for performance I don't doubt.

The adventures of Adam of hifiaf.com have produced an alternative way of adding mass for low compliance cartridges, which is to insert a tungsten rod into the headshell end of the right arm tube. The somewhat rubbery heat-shrink around the cartridge wires does a good job of coupling and grounding the rod. He is now happy with his Miyajima Zero/Blackbird setup. I'm sure he won't mind me posting one of his pictures here, as before:
IMG_9500.jpeg


Although Adam is using a tungsten rod in conjunction with the adjustable mass adaptor, this cartridge demands quite a heavy arm, and Adam reckons that the tungsten rod alone without the adjustable mass adaptor gives the arm a similar effective mass to an Ittok. I can also offer longer tungsten rods, so it will be more or less trivial to configure a Blackbird's mass for specific mid-to-low compliance cartridges without any visible paraphernalia.
 
I will have a stand in the fourth floor concourse near the bar(!) at the UK Hifi Show Live in Ascot (https://hifishowlive2022.eventbrite.co.uk or
www.hifishowlive.com) and I'm aiming to have four turntables sporting Blackbirds which you can listen to with headphones, Amadeus, Garrard 301, Sondek and Technics SL-1210. I understand there will be some used record dealers nearby, so instant gratification should be accommodated.

If you can make it, I look forward to seeing you there.
 
I was ‘away’ for the duration of this thread but have just read it start to finish. Absolutely awesome.
 
My personal view is the string lift (I know that’s been repeatedly covered) in combination with cart leads just sat there does not really do the arm justice. It has a plonked on a table top feel that lacks dynamism for want of a better word. Just IMO of course.

Good choice to show it on an LP12 obviously but I think the reverse is too cluttered. Personally I’d be brave and skip the random endorsements and stick to the tech.
 
I hadn't realised CDs had won, why hasn't anybody told me?

Apologies, I have nothing useful to suggest Richard, looks good to me.
 
Cheers Alex - views noted. it looks like I won't have time to alter this run of the flyer now, but your points will be in my ears for the next run.
 
My personal view is the string lift (I know that’s been repeatedly covered) in combination with cart leads just sat there does not really do the arm justice. It has a plonked on a table top feel that lacks dynamism for want of a better word. Just IMO of course.

Good choice to show it on an LP12 obviously but I think the reverse is too cluttered. Personally I’d be brave and skip the random endorsements and stick to the tech.
I disagree; I consider reviews by owners / users to be more valuable than what gets written by “professional” reviewers who are all in a symbiotic relationship with the manufacturers. And those are some eye catching endorsements!

I’ll call by and say hello on Saturday Richard.
 


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