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Turntable speed analysis part II

Discussion in 'd.i.y.' started by flavio81, Apr 18, 2012.

  1. flavio81

    flavio81 pfm Member

    What turntable is that? "Kuzma-esque"?

    The graphs look fantastic !
     
  2. NRG

    NRG pfm Member

    Many thanks Paul, was the file from my post 683 or 687?

    The motor layout is this:

    [​IMG]
     
  3. sq225917

    sq225917 situation engineer

    Thanks Paul, I must say I'm very pleased with the graphs, it really would appear that I'm at the limit of the test pressing. Now to reclaim that .4%. ;-)

    Flavio, it's a Kuzma Stabi/s 12" version. But I have replaced the bearing, subplatter,platter and motor with Lp12 parts and built a PSU based on a large isolating transformer and simple phase shift capacitor network. The real improvement comes from modifications to the bearing which has increased drag.
     
  4. YNWOAN

    YNWOAN 100% Analogue

  5. Paul R

    Paul R pfm Member

    683 wasn't there, so it's 687.

    Paul
     
  6. NRG

    NRG pfm Member

    OK thanks Paul, thats good, I'm happy with the results, a step forward...
     
  7. flavio81

    flavio81 pfm Member

    Thanks! I'm taking note, now attention on this: On the last 5 or 10 years some motor oil additives have appeared that use 'nanolubrication'. This is not quack science but real: These additives consist of extremely small (<0.1 micron) particles which 'stick' to the metal surfaces, evening them out so the finish is smoother (even if the metal was originally mirror polished!), significantly decreasing friction.

    I have seen tests of those additives firsthand and i can vouch that they do reduce metal-to-metal friction in an impressive way. As a car nerd, i wouldn't pour any of those substances in my engine so easily since motor oil has much more functions than just preventing metal-to-metal contact, but i feel that this should be an excellent additive to turntable bearings !!!

    Example of nanolubricant substances:
    http://www.lowerfriction.com/product-page.php?categoryID=19

    One of such products is "CERATEC" by Liqui-Moly. CERATEC is made of Hexagonal-Boron Nitride (hBN). "Liqui-moly" is known as "Lubro-moly" on the US, by the way.

    I shall be testing one of these days the addition of a similar additive to my turntables' bearings.
     
  8. flavio81

    flavio81 pfm Member

    (My assumption is that the increased but SMOOTH drag of your more viscous lubricant is overcoming the ROUGH drag of the turntable bearing... if we could smooth the bearing surfaces even more, then we can have a similar effect without having to increase the lubricant's viscosity)
     
  9. Joe

    Joe pfm Member

    He doesn't use motor oil.
     
  10. YNWOAN

    YNWOAN 100% Analogue

    This is not a bearing friction issue
     
  11. sq225917

    sq225917 situation engineer

    Flavio, you can polish your bearing all your like, it might make a tiny difference to the rotation of your deck. I wouldn't waste my time trying it.

    The issue seems to be that because of the low number of motor poles, and the large variation in attraction between rotor and poles across the course of one motor rotation that the motor will 'peak' as elements pass come towards other, increasing its ability to pull the belt, and 'trough' as the motor elements pass each other. The PL71 polar graph is a perfect example of this effect.

    Adding viscous damping to the bearing adds a constant, almost linear load to the bearing. The idea being that the increased load from drag swamps the variance in attractor between motor elements as it rotates. This would seem to be proved true by the results achieved.

    So you could polish your bearing to a mirror finish and that might even out bearing drag, but it will do nothing to damp the motor variance and it really is the effects of this 'cogging' in the motor that ruins speed stability.

    If you had a huge heavy platter and very weak motor, then maybe bearing smoothness would be important enough to worry about. In most decks it isn't.
     
  12. flavio81

    flavio81 pfm Member


    Understood and i think you guys are 100% right.

    But still i want to try this nanolubricant thing, it has the potential to reduce the noise floor IMO.
     
  13. YNWOAN

    YNWOAN 100% Analogue

    Ah well, that's quite another thing Flavio ;).

    When looking at the lubrication of a TT bearing, I would encourage you to consider the following aspects:

    What loads are applied ion the horizontal and vertical and how do these differ? What mechanism actually applies these loads?

    What the surface velocities of the moving surfaces are and what forces actually encourage oil to exist between those moving surfaces?

    What element may specifically be generating noise?

    I think that one of the major problems with turntable main bearings is that analogies are often drawn between them and motor car engines. In reality, there is very little in common between these bearing types - other than the fact that one surface rotates against another. Consider the environment within an engine, the velocity of rotating surface, the load applied - consider why oil is actively pressurised - what is pressuring the oil in a turntable bearing?
     
  14. edd9000

    edd9000 pfm Member

    I am not sure you are still interested.

    In the process of building my diy turntable I became interested in measuring its performance. Are you willing to share the software you are using?

    This is the only recording i have to share right now:

    http://www.mediafire.com/?xz2us79ggicm9oz

    Its from a yamaha yp-d71 direct drive. Analogue productions 3150hz signal.

    I forgot to keep the recordings from my diy turntable, I hope to have more soon.
     
  15. edd9000

    edd9000 pfm Member

    FM demodulating the above with a 20hz bandwidth in Spectrum Lab, then plotting the FFT in rightmark I get this:

    [​IMG]
     
  16. John Channing

    John Channing fruit box forever

    That is interesting, I had always wondered why multi-motor designs like the Voyd worked and that could be the answer - if you align the peaks and troughs from different motors, you get a smoother total torque. It would be interesting to be able to directly measure these torque ripples, I note from a quick internet search this data is not on any motor spec sheets.


    This idea has been used on the Bauer DPS
     
  17. darrylfunk

    darrylfunk Banned

    yeah my lovely loth x othello had a large oil capacity giving a resistance to the load.

    until a linn dealer farked the bearing when putting a cartridge on....heaven only knows why they even fiddled with the bearing.

    it did used to need a good 15 minutes for the pitch to stabilise though.
     
  18. Paul R

    Paul R pfm Member

    This is still an ongoing project.

    At the moment I'm not willing to support it, so it seems best to keep it in house.

    I'll process your file and see if it matches your result.

    Paul
     
  19. edd9000

    edd9000 pfm Member

    No problem on the software. I re-read the thread and had previously missed the discusion on it. I will keep playing with gnuplot and see if i can find something that will generate enough data points for a meaningfull fft with it.
     
  20. madmike

    madmike I feel much better now, I really do...

    So would that be multi motor, or viscous damping ?...or both ?

    I have a Transcriptors reference which has the latter.
     

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