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

Discussion in 'audio' started by sonddek, Sep 20, 2020.

  1. sonddek

    sonddek Trade: SUPATRAC

    It's a very small issue, possibly inaudible, and it is fixed by a very small adjustment in hoist angle.
     
    Garrard 401 and Rockhopper like this.
  2. yuckyamson

    yuckyamson pfm Member

    Again, sorry if this is creating "noise" in the communication (pun intended), but do I have it right that you've now made the hoist sit vertical (i.e. no underhang), and thus the only effect when twisting left/right away from "record middle" (call it "track 3") will be one of skate/antiskate, which you're adjusting for in your antiskate mechanism. Correct?

    I kind of liked the underhang to apply forward pressure from the thrust plate onto the pivot point. If you're now using a magnet, is there a chance that as the pivot swings l/r ever so slightly that the magnet will not have continuous effect on the pivot? That it could be pulling it one-way or the other, rather than just at the thrust plate?
     
  3. sonddek

    sonddek Trade: SUPATRAC

    Yes, correct.

    The magnet will be optional, just as it was in my prototypes. Some people may decide that the degree of lean variation is barely or not audible and prefer to use the arm without a magnet for simplicity's sake.

    The requirement for very light pressure at the pivot point is or can be supplied in three ways: stylus drag (not optional), gravity/underhang (optional) and magnetism (optional). My view is that stylus drag is not enough on its own to guarantee good performance unless you tilt your deck, in which case you're using gravity but not underhang. If you use too much underhang the rotational plane of the arm and record do not match perfectly and there will be a tiny variation in lean across the record.

    I intend to send both a stainless steel (tungsten-tipped) pivot bolt and a magnetised mild steel (tungsten-tipped) pivot bolt with each arm. A small magnet can also be placed on the end of the pivot bolt to increase the pull at the pivot point. The magnetic pull is small, but enough, so although you are right about variation in the pull of the magnet as the arm yaws, the angle of use is 18º or less, and I do not expect this to be a source of significant error in skate forces, especially when you consider that correct skate force is also signal-dependent. Roughly right net anti-skate, the best that one can do on any pivot arm, will remain roughly right net anti-skate.

    Either way, with a light touch of magnetism or underhang, the arm will continue to produce astounding performance. I hope that all makes sense.
     
    Last edited: Oct 25, 2021
  4. yuckyamson

    yuckyamson pfm Member

    It makes sense. Without having used it, I'd be more inclined to use underhang than add a magnetic field into the mix, but that's all just in my head and if there's one thing I've learned, it's that the imagined physics of audio don't always translate when you try something and listen to it, and learn from there. The bottom line is that Adam said that this arm, in no uncertain terms, was better than his ekos, aro, and javelin, and he wasn't making any bones about it. So that to me is high praise. Perhaps in future iterations you will have a more refined version, or another solution still implimenting the sideways unipivot. I rather love the concept.
     
    sonddek likes this.
  5. sq225917

    sq225917 Bit of this, bit of that

    It's a unique approach to the task at hand and one that does away with most of the issues that plague certain unipivot designs and chattering gimbal arms.
     
    sonddek likes this.
  6. sonddek

    sonddek Trade: SUPATRAC

    At LencoHeaven Billy says it is better than his Audiomods 6, Arndt thinks it helped him install what some said was the best system at the Berlin Audio Meet, and about ten people have made clones of varying sophistication, all of whom report unprecedented performance. More arms are going out as I produce, and I now expect there will be many more surprising reports. Meanwhile I don't get enough time each day to listen to those archaic black discs! ;-)
     
  7. sonddek

    sonddek Trade: SUPATRAC

    I don't know when 'production' can be said to have started, but I'm 'gearing up'...

    [​IMG]
     
    Dan K, Garrard 401, Dark Lord and 7 others like this.
  8. sonddek

    sonddek Trade: SUPATRAC

    A brief update: for the time being, only the Death Star thrust boxes will be available for new orders. The Aero version may be available again in the future, but probably not for a few months. The reason is simply to do with ordering batches of parts, as I'm sure you will understand. If you're desperate for Aero, then I can make one for you, but I will have to charge an additional fee because of the time it takes me to make parts myself instead of having them made elsewhere. All thrust boxes are now painted and have channels to make room for vertical hoists/magnetic bearing contact.
     
  9. sonddek

    sonddek Trade: SUPATRAC

    The string lifter has now been sighted on Schröder and Javelin arms...

    [​IMG]
     
    Darren L likes this.
  10. sonddek

    sonddek Trade: SUPATRAC

    Even the faithful Ittok can have a significant usability upgrade after all these years ;-)

    [​IMG]
     
  11. Craig B

    Craig B Re:trophile

    That reminds me, we had a lovely looking pair of cardinals at the feeder this morning.
     
    sonddek likes this.
  12. sonddek

    sonddek Trade: SUPATRAC

    The first VPI compatible Blackbird has been installed by its new owner today. He says...

    "First impressions are excellent, definitely leaves the JMW Memorial Tonearm in the dust. More Bass and tighter, separation is excellent and overall great soundstage. Working through a load of albums as we speak and loving what I am hearing."
     
    Last edited: Dec 21, 2021
  13. Waxxy

    Waxxy pfm Member

    Ahem! I have a VPI Aries II. What in particular is needed make the Blackbird compatible with a VPI?
     
  14. sonddek

    sonddek Trade: SUPATRAC

    The pillar and base are narrower than the Linn/SME, Rega and Jelco mounts. I made a 15mm diameter pillar which still has room for a 12mm DIN plug in the base. There isn't room for the arm support post within the 15mm diameter so it has to be off centre like a crank shaft. The base has countersunk bolt holes at the appropriate radius. I'll see if I can get some photographs.
     
    Waxxy likes this.
  15. sonddek

    sonddek Trade: SUPATRAC

    Meanwhile, time for a supasnac.

    [​IMG]
     
    nobeone likes this.
  16. sonddek

    sonddek Trade: SUPATRAC

    As promised, a photo with kind permission of the owner:

    [​IMG]

    Although it's slightly beyond depth of focus, in this crop you can see the cam shaft style of the post and narrow pillar. Note also the neodymium magnets perched on the near end of the pivot bolt:

    [​IMG]


    The thrust box has counters to avoid contact with the hoists above the flex points, so the hoist plane can be vertical, ensuring consistent azimuth while adequate contact force at the bearing is supplied by the magnets and stylus drag. The offset post allows the pivot to be on the vertical axis of the pillar so rotation of the pillar in the base does not alter spindle-to-pivot distance, and this facilitates optimising bias using the three factors, pivot orientation, bias pulley length and bias weight displacement from the rotor axis. This mechanism allows you to adjust both the average bias and the rate of change of bias across the record. It is easier done than said.
     
    Waxxy likes this.
  17. Waxxy

    Waxxy pfm Member

    Thanks so much for the prompt and detailed reply.
     
  18. sonddek

    sonddek Trade: SUPATRAC

    No problem - please don't hesitate to ask if you have any other questions.
     
  19. sonddek

    sonddek Trade: SUPATRAC

    It might look slightly less odd if I explain that my children were making Christmas biscuits in funny shapes – snow flakes, stars, what-have-you – and they've noticed that I've been concentrating quite hard on making tonearms, hence the birth of the supasnac.
     
    Last edited: Dec 31, 2021
  20. sonddek

    sonddek Trade: SUPATRAC

    I'm pleased to say that Blackbird arms have been sent to everyone who has paid for one in 2021.

    Two consigned orders are with couriers and still to arrive in Canada and New Zealand.

    Have a magnificent 2022!
     
    tiggers, Dark Lord and Iain Docherty like this.

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