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Physical comparison of three LP12 subchassis: Linn Kore, Greenstreet, Mober

Discussion in 'audio' started by anhammond, Nov 10, 2019.

  1. anhammond

    anhammond Member

    I'm in the midst of a needlessly thorough comparison of various LP12 components, and so I found myself with three subchassis. I thought I would take as many measurements as I could, since I'm curious about these kinds of things.

    Here's what they look like:

    [​IMG]
    Linn Kore

    [​IMG]
    Greenstreet for Aro (logo added by previous owner)

    [​IMG]
    Mober for Rega.

    First thing I measured was weight. They’re all quite similar in mass. The Kore is heaviest at 1102g, followed by the Greenstreet at 1033g, followed by the Mober at 1011g.

    Next up: centre of gravity / balance point. I've indicated it in the following photos with a spot of blu-tack. The Mober and Greenstreet are in exactly the same spot, 14.3cm from the edge of the armboard; the Kore is further from the motor, 13.3cm from the armboard.

    [​IMG]
    Kore

    [​IMG]
    Greenstreet

    [​IMG]
    Mober

    Finally — most excitingly for me (I need to get a life!) — tap tone. I wasn't able to upload audio here, so you'll need to visit my blog here to hear them, or click on the links below.

    The Kore is by far the least resonant. This is what it sounds like when you knock it with your knuckle while suspending it from a string: (sound here). Frequency analysis of this tone in Audacity suggests the Kore resonates at 407 Hz (G#4).

    The Greenstreet rings much louder and longer (sound here). Audacity has it resonating at about the same frequency as the Kore: 415 Hz, also G#4.

    The Mober rings loudest and longest (sound here), with a different frequency to the other two. Audacity has it at 699 Hz (F5).

    See my blog post for more and larger photos, including screen grabs of the Audacity frequency analysis of each tap tone.

    http://www.hifiaf.com/three-lp12-subchassis/

    Thus ends a thorough treatment of a subject of very limited interest.
     
    McNaim, Drumossie, rontoolsie and 5 others like this.
  2. sq225917

    sq225917 situation engineer

    What's the balance point with the arms on, I notice each is for a different arm.
     
  3. DavidS

    DavidS pfm Member

    You're right , you need to get out more.
     
  4. YNWOAN

    YNWOAN 100% Analogue

    I’m not surprised the Kore is the most damped, I’m more surprised it rings as much as it does; of course the Keel will ring strongly, much as the GS and the Mober. I’m also surprised the ring tone is so different for the GS and Mober and suspect this is down to the specific grade of aluminium that they are machined from.
     
  5. Darren

    Darren All Business

    More interesting than I initially thought! The three make very different ringing noises.
    I don't think you should get out more.... I think you should stay at home and experiment further.
     
    anhammond likes this.
  6. anhammond

    anhammond Member

    Thanks for the support, Darren :)

    sq225917, that's a good question. I've already installed the Mober, so late for now, but I can check on the rest. My guess is that the differences aren't enough to compensate for the difference in mass between, say, a very lightweight Nima and a heavier Ekos. But I'll check it out with the Aro and the Ekos, and the Mober sometime when I have it out of the deck.

    YNWOAN, I'm a total amateur in such matters, but I wondered if the rather different shape of the Mober, with the cutouts around the bearing attachment, might contribute to its different ring tone.
     
  7. YNWOAN

    YNWOAN 100% Analogue

    Given the similarities in overall weight I would be surprised if the, relatively small, variations in the centres of gravity would have any appreciable effect.

    The cutouts will, I agree, have some impact but I’m surprised it is as great as it is. For what it’s worth, I don’t think the Mober is anodised black, at least not in the same sense the GS is, and the change in finish will have some impact on the ringing (not much though).

    ——-
    May I suggest this further experiment? Fit the main bearing and the inner and outer platters (make sure oil is in the bearing). Support each chassis on the springs and grommets arrangement and try your experiment again - that would be very interesting.

    If one uses a stethoscope and are able to place it against the armboard, or chassis, whilst a record is playing (amplifier turned off), it is very easy to hear the music - vibration passes down the armtube and into the armboard/chassis. Some of this music will find itself back into the arm and back to the cartridge - this is the primary mechanism by which the armboard and chassis impact upon the sound (colour it).
     
    anhammond likes this.
  8. anhammond

    anhammond Member

    YNWOAN, this experiment will take a while, but I'll do it. I imagine there are stethoscopes with digital outputs? Any suggestion for a test track for this experiment? I suppose anything well-known will do.
     
  9. YNWOAN

    YNWOAN 100% Analogue

    Oh, I meant just record the ringing noise as you did before, but with the added pressure load of the platter and the parasitic elements of the suspension and platter :). The music doesn’t matter in this context as it’s actually extremely easy to hear the echo of any track played - you can easily recognise the music.
     
    anhammond likes this.
  10. nobeone

    nobeone pfm Member

    Makes me think Stack might be on to something with their material choice for the Serene parts? No appreciable ringing when I tapped the base plate ...
     
  11. sq225917

    sq225917 situation engineer

    Anyone ever seen proof of ringing on a measured lp12 during playback? It's mostly motor noise and rumble.
     
  12. anhammond

    anhammond Member

    Ah yes, YNWOAN, that makes sense :) I'll do that next time I have all the parts out (I don't have any spare bearings to do this with now). If you're interested in the knock tone of the Mober fully installed, however (I did put it in yesterday), here it is. Not much ringing in the full system, so perhaps the ringing in isolation isn't very important. Although I don't hear much of a tone of any kind, Audacity reads this having a peak frequency of 496 Hz — different from the subchassis in isolation. The next peak is at 689 Hz, close to the Mober's resonant frequency of 699 Hz.
     
    YNWOAN likes this.
  13. sq225917

    sq225917 situation engineer

    That the point I was making, once assembled the effect is nothing like the sub chassis on its Todd.
     
  14. TheDecameron

    TheDecameron Unicorns fart glitter.

    Great thread topic! are you planning to run comparative SQ assessment? I bought the Mober on spec because it’s the best price, got it fitted by J7. Have to say it’s a huge improvement on the Linn 80s bonded sub-chassis.. it’s such a shame Linn weren’t doing this themselves back then.
     
    anhammond and Hove 100 like this.
  15. anhammond

    anhammond Member

    Yes, I have a whole ridiculously elaborate methodology set up for evaluating each the deck every time I make a change. The basic story is here. In brief, I have a bunch of test tracks that I will compare A/B against my decent digital rig whenever I make any kind of upgrade to my LP12. I've described the test tracks and test albums here. I'm working up my "before" article now from notes I made over the last week.

    I've spent today listening to the deck with the Mober installed. Though this is NOT based on an A/B comparison against a digital baseline, so far the music does sound amazing (and, to use a dumb but effective word, better) with the Mober than with the Cirkus subchassis + laminated armboard. I will use smarter words after I've spent a few months listening to my test albums and done my A/B comparison. Then I'll make another modification!
     
    YNWOAN, Ian M, sq225917 and 2 others like this.
  16. McNaim

    McNaim pfm Member

    Hello anhammond, great topic and great blog. You have found a follower :)
     

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