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Poul Ladegaard's Air Bearing Tangential Tonearm - has anyone here built one?

Discussion in 'd.i.y.' started by Rosewind, Jan 12, 2019.

  1. Rosewind

    Rosewind Lost in Translation

    I will build the air bearing arm with what I bought now or have in the house. It will be placed on a movable tray that I can place in front of the turntable when I need to test things. I will work methodically on this.

    Surely it would be useful to have a second turntable available. However, I do not have a place for it.
     
    Last edited: Jan 17, 2019
  2. davidsrsb

    davidsrsb pfm Member

    I find it hard to believe that an air bearing does not suffer from turbulence causing vibration at the record groove scale
     
  3. Rosewind

    Rosewind Lost in Translation

    I am certain that this has been discussed in one of the long, long threads on diyAudio. The Trans-Fi terminator arm uses the same basic idea. So ...
     
  4. h.g.

    h.g. pfm Member

    The air flow is laminar not turbulent. The lack of friction (i.e. damping) is not ideal as shown in one of Rosewind's links. A small amount would be helpful. The vertical compliance may be a help, hindrance or unimportant would need to think more. The vertical and horizontal mass of the arm are strongly different which may be helpful or a hindrance. Before starting the construction of such an an arm I intend to construct a numerical model to address a few questions like this.
     
  5. davidsrsb

    davidsrsb pfm Member

    Achieving ideal laminar flow is incredibly hard, with dust, imperfections in finish and so on. Any audible hiss at all is a sign of turbulence
     
  6. h.g.

    h.g. pfm Member

    An air bearing requires the viscous forces to dominate the inertia forces in order to function as intended. Turbulence occurs when it is the other way round. Dust particles and such will introduce friction but the air flow around them will remain laminar not turbulent. In the case of this arm a bit of damping/friction is desirable but if I recall correctly from the link the desired amount of damping was only achieved when the bearing was starting to stick. Nonetheless it is something to think about.

    Laminar flows may be unstable. Vortex shedding behind a wire at low Reynolds number would be an example. A flute at low Reynolds number another. They are characterised by fairly pure tones and so would be more of a whistle than a hiss. So if it was a hiss and not a whistle and was coming from the air bearing and not somewhere else then I would agree that the air bearing would be in trouble. Has this been a reported problem with the arms that have been built so far?

    Having said that, the vibration of the cartridge by the arm needs to be minimised. The air bearing would seem more compliant than the solid bearing of a conventional arm when it comes to the vibration of the chassis being transmitted to the arm. This may provide better isolation at higher frequencies but also may (or may not) introduce an unwanted resonance at a low frequency. I haven't done the sums but it is the type of thing simulation would address.
     
  7. Rosewind

    Rosewind Lost in Translation

  8. Rosewind

    Rosewind Lost in Translation

    Last edited: Jan 20, 2019
    h.g. likes this.
  9. Rosewind

    Rosewind Lost in Translation

    Today I did two things: (1) Bought a cheap headshell from China that I will receive in about a month, (2) Cut out a DIY headshell from a paint mixer stick 2cm by 5 cm. I will need to drill holes for mounting it - at one end 2 holes for the cart, at the other end one hole for attaching it to the arm, then device a small lifter for it, sand it, possibly stain it and prime it.

    The idea is to cut the wood arm tube flat at the headshell end, drill a hole through the arm wand and attach the wood headshell there (model photo not of wood wand obviously):
    [​IMG]
     
  10. h.g.

    h.g. pfm Member

    Interesting. It addresses one or two things nicely in exchange for one or two weaker points like the handling of some record imperfections. Not that I have fully worked out the pros and cons yet. Several of the claims are too strong with respect to damping, mass and resonances but, again, a numerical model would help optimise that sort of thing. Tempting...
     
  11. Rosewind

    Rosewind Lost in Translation

    I am slowly gathering the parts for this.

    A friend of mine has a bog standard Lenco 75 that I may borrow for setting up the arm.

    Knife bearing: I have some stanley knife blades in the house, and have found two rounded bolts with threaded ends and an aluminum angle (1 x 15 x 15 mm) to hold the blade in place. Should work.

    Counterweight: I am going to use a spare one from my Thorens TP 16 arm and possibly leave it dangling from the arm in two threads/wires.

    Arm: I have 4 different wood duwels en route to me. I will pick the leightest one. If that does not work out, I will hunt down a carbon fiber wand from a s/h badminton racket or an arrow. Flexible arm wire with cartridge connectors is also on its way to me and I am sure I can scavenge some RCA plugs from some of the spare cables I have in the house. I have an old Ortofon OM10 cart in the house.

    Headshell: I have a DIY wood one, and a metal one on its way to me.

    Air bearing sleigh: I have an anodised 2x20x20 mm angular aluminum profile en route to me, double sided foam tape, and regular tape at hand. I need to buy an air intake connector. I will need to find a way to support the air bearing unit.

    I will need a suitable air pump and a way to regulate the air-flow.
     
  12. Paul R

    Paul R pfm Member

    You can buy various diameters of carbon tubing from model type shops and equivalent online suppliers. You will probably find thin wall aluminium tube in the same places. If you have one locally then being able to handle the material might be useful.

    Aluminium is tempting to me because the end could be squashed flat giving a surface to clamp the cartridge against without needing much in the way of fabrication skill...
     
  13. Rosewind

    Rosewind Lost in Translation

    Paul, I will check those two options out I am sure.
    I just received the aluminum angles, which looks fine, however, the outside angle is rounded whereas the inside angle is straight. Will this be a problem, I wonder?
    [​IMG]

    I also received the arm wire and arm connectors from Trans Fi

    [​IMG]
     
  14. Paul R

    Paul R pfm Member

    I think the aluminium will be fine, the bearing surface is on the flat parts not in the vee. So as long as the pieces fit closely together should be fine.

    I used the Transfi supplied cable/cartridge connector set to rewire my broken RB300 some years ago. IIRC the best approach is to burn the insulation off at the time of soldering, but perhaps it mentions that somewhere.
     
  15. Rosewind

    Rosewind Lost in Translation

    Thanks Paul. The pieces do fit together

    I found a description of how to work with the wire on the Trans Fi home page, so I should be ok if am able to follow the proper procedure laid out there.

    I may have a little time to cut the angles and perhaps drill the holes this weekend. Assembly will have to wait until the coming Thursday and Friday when I am off from work.
     
  16. Rosewind

    Rosewind Lost in Translation

    The aluminium angles ARE NOT 20mm x 20 mm - they are 19mm x 20.2 mm or so - which means that the angles HAVE NOT BEEN BENT/SHAPED symmetrically. That buggers up the air bearing sled because I need that to be perfectly balanced. I got as far as cutting two of the pieces in the correct lengths of 2 pieces measuring 30 cm before I noticed that the sides are of unequal width when I put the two parts together. #%&%#!!!!

    I will se what the eBay seller says to this. I think that a 1 mm deviance/intolerance from 20mm x 20 mm specs is too much. Lengthwise I couldn't have cared less.

    [​IMG]
     
    Last edited: Jan 26, 2019
  17. YNWOAN

    YNWOAN 100% Analogue

    The air flow in the ladegaard is not laminar because turbulence is generated at the edges between the sled and the support, not to mention the fact that air flow is never entirely even from the pump (both long recognised issues with air bearing arms). The concept is simple but the application involves so many compromises it introduces more problems than it solves.
     
  18. Rosewind

    Rosewind Lost in Translation

    I know that some builders have used two air inputs whereas others have used one. I also know that some builders have used a tank between the pump and the air bearing input to try to even out pressure fluctuations.

    As far as I know no arm build method has been able to create the perfect environment with zero drawbacks for a turntable arm. I am sure some arm builds come very close to perfection but they do so at a cost. And what cost.
     
  19. Rosewind

    Rosewind Lost in Translation

    If I settle for one air intake, where would the best location for it be? - dead centre or at the end? - or doesn't it matter?

    Which silent type of fish tank pump would be perfect?
    It has to be one that is readily available in the EU.

    As for the angles and other materials, from now on, I will buy from local stores so I can handle and measure everything prior to purchase. Lesson learned.
     
  20. YNWOAN

    YNWOAN 100% Analogue

    You would be better off buying an air bearing designed for the purpose rather than cobbling one together in the way transfi does. Designs where a sled rides on a rail carry inherent compromises that cannot be overcome. You need a constrained design where the bearing surrounds a shaft. Look at the Kuzma where a porous material is used - the bearing Kuzma use can be bought.

    As for in line surge tanks - at least one absolutely must be used otherwise every action of the pump will be directly passed to the bearing - in effect, you are actively vibrating the arm bearing.

    DIY air bearings are, by their very nature, low tolerance and flexible.

    Also, bear in mind that the air delivery tube (in particular) and arm wiring apply significant forces to the arm bearing as the arm moves and can easily overcome the benefit of the low friction of the air bearing principle. In addition, air bearing tangential arms, unlike any other design, are hyper sensitive to absolute level during play. Any deviation from absolute level (and I do mean absolute level) will mean that the mass of the arm supporting carriage will apply really significant side force to the stylus in a way that doesn’t exist in any other arm type. In short, whilst tangential air bearing arms do overcome end of side tracking distortion they are worse in every other aspect of performance than a pivoted design.
     

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