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

RichShortland said:
- the foam filling of (half) of the arm tube. Was this for damping or to increase / manage the effective mass? The reason I ask is that my WT copy has an aluminium/carbon arrow as an arm tube and it is unfilled (and very light) at present, whereas the WT arm is filled with sand or foam I think... wondering if I should do some sort of fill, but it is very difficult to undo!
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It's for damping. The increase in mass is very small. The WT arms are filled with sand which is heavy and non-rigid. One of my prejudices is that I think the best kind of damping is rigidity, and lots of it.

- if I've understood the the hoist wires correctly, they are there to support the 'thrust box' until load is introduced to the side bearing by the stylus drag, and also a job of reducing side to side rolling. There is the risk this design introduces vibration or removes the efficiency of the single point of contact bearing somewhat, so I was wondering if there was any merit in attempting a design which minimised the need for the hoist such as having the pivot angled at say, 45 degrees instead of 90, taking 'some' of the vertical load..? How valuable is the lack of side to side yaw vs the impact of the hoist wires do you think?
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The hoists support the arm (including thrust box) against gravity at all times. Their geometry inhibits roll and stops the arm falling down. The extent to which vibration is 'introduced' by signal is unknown, but I considered it of minor importance because the arm is grounded at the pivot point which is oriented successfully to oppose the principal forces from the cartridge. The hoists are made from a longitudinally inelastic material. They are virtually powerless to inhibit yaw and pitch movements of the arm so I surmise that they will not absorb much energy from the cartridge. I considered a 45 degree pivot at the design stage, but it would have to be higher so as not to introduce instability, and it would be inclined to rub like a traditional uni-pivot when signal oscillations start to pull. The virtue of the sideways uni-pivot is that it orthogonally opposes the fluctuations of stylus drag with minimal contact force.

Thanks very much. And for what it's worth I love the idea of the string finger lift. I'm going to give that a try in my WT clone as I hate cueing the thing manually using a rigid finger lift at present as it has such a low effective mass...
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I've been using the alternative rigid finger lifter on one of my Blackbirds for a few days now. It's about as good as rigid finger lifters get, but no match for the safe and comfortable use of the string. The key advantage of the string is that you get a confirmed grip on the string between thumb and forefinger while the record is still playing. There is no quantum leap between the two states of playing and lifted. They overlap. All the neurosis happens in the narrow gap between playing and secured.

Cheers!
 
divedeepdog said:
Any thoughts on longer length? I suspect 10”+ would look great on a 401 and make fitting easier…
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Many of the people ordering a Blackbird are requesting longer arms. I can cut the arm to any length. Don't forget serial number 1 was a 12.5 inch arm for the left mount on a SL-1000R.

If you supply your spindle-to-pivot distance I can supply the Blackbird in the optimal length/offset for your deck.
 
Very, very well done on this, awesome to see a one man band come up with something new and interesting. You have some engineering skills. I may well be a future customer!
 
Over on Lencoheaven some diy enthusiasts have built their own versions of the SUPA. They all report unprecedented performance. I hope it's OK to post an example of such reports here:

Your comment- Great design! I wonder why no one has thought of this in the last 100 years.

I believe creative thinking in hi fi has been notably absent in the commercial field for many years.
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Think about the loudspeaker- the basics have been unchanged for decades. I've been side-tracked in my arm designs by trying different materials for arm tubes but using the same unipivot principle and the differences have at best been marginal.
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I still might experiment with different materials for the arm tube but I'm afraid that the conventional unipivot bearing is no longer a viable consideration for me. Now that's pretty exciting don't you think?
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It's not that the conventional unipivot is rubbish (I'm really pleased with the results obtained to date) but Richard's design is something else...
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Evidence that this bearing design is "a game changer" seems to be accumulating and sets me thinking about those soon to hear Amelita's high C without disappointment! ;-)
 
I'm frustratingly close to sending out the next batch of arms. In the meantime, here's the new cover for the manual:

manualfront.jpg
 
I don't see the point in offering two fractionally different styles of thrust box. It's unnecessary complication, no one else does anything like that.
 
Mr Pig said:
I don't see the point in offering two fractionally different styles of thrust box. It's unnecessary complication, no one else does anything like that.
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I may terminate one of them if the other proves more popular, or if I start to get them made elsewhere. For the moment they take me about the same time to produce. Some customers already have examples of each. It's just a bit of fun really. Both are hard work to make by hand, that's for sure. It's not impossible that I will revert to no holes at the back if I get the time to test performance and reckon the effect is inaudible.
 
Mr Pig said:
I don't see the point in offering two fractionally different styles of thrust box. It's unnecessary complication, no one else does anything like that.
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No one else does a lot of things this arm does so I think it's rather up to sonddek if he chooses to offer both alternatives.
 
tiggers said:
No one else does a lot of things this arm does so I think it's rather up to sonddek if he chooses to offer both alternatives.
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The customer is in charge! Unfortunately, so far, customer choice is evenly split between the two schemes, so I've made a rod for my back. When I start to get them made by an external manufacturer I may have to drop one option, or add a premium for it to be handmade.
 
Mr Pig said:
How do you lift that arm? It has no arm-lift and no finger lift on the headshell.
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It was just being tested before being sent to a customer. The front face is now filed and the string is in.

The base bolts flush with the plinth, but has an offset locking bolt so that you can release the pillar from the top to adjust VTA. It will be painted black.
 
This seems like a very impressive arm. Very outside-the-box thinking. But honestly, you have to give up on the string lift. It really just cheapens the look and takes away the fact that this is now, in fact, a consumer ready product, vs a diy exercise. And I understand you find the string easy to use, but sometimes sacrifices must be made for aesthetics. Sticking with just the normal lift is definitely the way to go.
 
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