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Directions in SPUs - Tonearms, advice sought, reflections on gear...

Discussion in 'classic' started by naimnut, Dec 22, 2021.

  1. naimnut

    naimnut Deep in the Mines of Soul

    Just remembered a question that someone here might be able to answer. What makes an arm "high mass"? Is it the overall design and actual weight of the complete tonearm? If so, are arms like the Ortofon RS309, Groovemaster and Schick considered high mass? Or can the weight of the counterweight be factored in to adapt a "normal" arm, like a Jelco, to be used satisfactorily with an SPU?
     
  2. montesquieu

    montesquieu pfm Member

    It's complicated - certainly more complicated than simply based on the stylus pressure at the end. The overall mass (tonearm + headshell + cartridge) drives the resonance behaviour of the entire system. Mass calculations can be impacted by how the mass is distributed along the arm tube and even by the relative position of the counterweight.

    Resonance is best checked using a test record. Calculators are available to work this out on Vinyl Engine but assumes correct inputs and very often specs for tonearm mass much-repeated on forums are inaccurate, as are quite a lot of cartridge specs (not least as many Japanese cartridges quote dynamic compliance at 100hz rather than the 10hz required by the calculator).

    BTW you really don't need a Glanz arm to get the best out of an SPU, for a 9in arm, a used SME M2-9R or a Fidelity Research FR64S would be my choice. For a new arm the Schick or the Groovemaster/Timestep are excellent and certainly less of a lottery when it comes to bearing condition etc.
     
    naimnut likes this.
  3. naimnut

    naimnut Deep in the Mines of Soul

    IIRC I've read somewhere that some of the Ortofon and SME arms were made in Japan. Do you know whether this is true?
     
  4. Tony L

    Tony L Administrator

    I’d argue no arm capable of balancing out a 30g+ SPU head could ever be described as low mass! Even something like a 3009 Improved becomes high-mass if you can ever find the additional very heavy counterweight required for the SPU. It certainly isn’t about the arm-tube to any great degree, mass at either end has a far greater impact, though I just don’t have the maths education to be able to articulate that in figures. A 12” arm will inevitably be much higher mass than a 9” arm as you need a way bigger counterweight at the back to balance-out a 30g+ SPU. On paper the difference in effective mass between a 3009 Series II and a 3012 is only 3g, but once you start playing with such heavy cartridges that number will increase.
     
    naimnut likes this.
  5. daytona600

    daytona600 Registered User

  6. Nagraboy

    Nagraboy How’d all these people get in my room?

    @naimnut

    I’m keen on the Schick too but there’s no way to hear one and setting it up could be a nightmare with no experience - wobbly scales and judging things by eye etc. Too much money to spend and end up with a botched job.
     
    naimnut likes this.
  7. montesquieu

    montesquieu pfm Member


    I wouldn't personally use an SME 3009 improved (the lightweight one) with an SPU, though an earlier non-improved one will probably be OK. The higher mass M2-9R is better than either. I stand by the point that the whole thing should be looked at as a system. It's not true that the arm wand mass has no impact - it depends hugely on specifics of the arm wand, whether it tapers or bends, and its relative contribution to the overall mass. Consider a swinging stick that's the same thickness all the way through, and a thinner stick with a weight on the end - the mass distribution will influence how it moves and handles, and will certainly impact the resonance behaviour which is the important factor here.

    There was a good thread in Vinyl Engine a few years back that goes into some of this https://www.vinylengine.com/turntable_forum/viewtopic.php?t=77151

    While it's true that in principle that a 12in arm, all other things being equal, will have higher mass than a 9in arm, it's not necessarily the case when comparing different designs that are not equal- a 9in Ikeda or Glanz or FR64S will be higher effective mass than many 12in arms for example, eg an SME V12 or possibly even some flavours of SME 3012. Indeed according to my resonance tests my old late model shiny/heavy chromed 9in Ikeda IT-345 CR1 was very slightly higher mass than my very early, non-chrome 12in Ikeda IT-407 from 30 years previous.
     
  8. montesquieu

    montesquieu pfm Member


    Ortofon AS 212 tonearm arm by the looks of it. Definitely a Garrard 401.
     
  9. Tony L

    Tony L Administrator

    I’m kind of gently trolling to question some of the received wisdom with the SPU. I’d not use an Improved either, plus I bet you’d have to pay £300 for the SPU counterweight if you could even find one (absolute hens teeth!). They do seem to work ok in a Series II if you can find a 3012 counterweight to balance things out easily. If I ever tried one that is likely how I’d do it.

    Anyway, what has me curious is the maths. An SPU is a very, very heavy head with a 10cu compliance. In its day it was routinely partnered with 9” & 12” Ortofon and SME arms, all of which are medium mass as far as I can tell, though necessitating a heavy counterweight to balance out the SPU (an option on the SME). I know the original 1959 SME Series I was a heavier arm, but they are just crazy rare and AIUI only a few hundred were made before the ubiquitous Series II arrived in 1961. The vast majority would have been used in Ortofon arms or Series II SMEs.

    [​IMG]

    Here’s a simple mass/compliance calculator. A 10cu cart does not need the simply crazy levels of mass sticking a 30g+ SPU head in a FR66 or whatever would give. As stated my maths and grasp of physics really isn’t of the level of being able to calculate what sticking such a heavy head in such an arm would result in, but my bet is a period-correct ‘60s Ortofon or SME would be in the blue safe zone, and the FR or Ikeda not. This is one of those areas of audio that is actually maths.

    PS Jimi’s deck is a good example of what I mean. That is the context Ortofon sold them to be used in.
     
  10. montesquieu

    montesquieu pfm Member

    Yes that all makes sense ... bear in mind it's the earlier (vintage/alnico) SPUs that have a nominal compliance of 10 (I would say that's an average .. I'm sure it varied quite a lot in practice between versions and over time as suspensions stiffen in many cases) but the majority of the newer production SPUs have a compliance of 8 so a bit more borderline on this model.

    Yes at one point I had the RMG309 Limited (basically the RMG309i with an SME-style sliding/adjustable base plate) which was made in Japan in the 1990s, based on and original Ortofon tonearm from the 1960s. Japan was where the SPU revival began and as I understand when Ortofon started making SPUs again in the late 80s or early 90s after a bit of a gap, the first production was Japan only. Obviously some enthusiasts wanted a tonearm to go with the cartridge ...

    edit - found it! If memory serves, there was a suggestion it was made for Ortofon by Audiocraft (later of course Ortofon contracted Jelco to make some of their tonearms).

    [​IMG]

    [​IMG]
     
    G T Audio likes this.
  11. daytona600

    daytona600 Registered User

    Effective tonearm mass in grams including Alu headshell 19.5
    A unique counterweight construction allows you to balance cartridges from 5 up to 25 grams (excluding headshell) depending on weight of the chosen headshell (up to 37 grams with ´Alu´, up to 39 grams with ´Carbon´, up to 41 grams with ´Wood´). So, this is also an ideal tonearm for direct mounting of SPU cartridges.
    [​IMG]
     
  12. montesquieu

    montesquieu pfm Member

    Looks like pretty decent value at list price. And shiny. I like shiny.
     
  13. naimnut

    naimnut Deep in the Mines of Soul

    Those photos are really helpful. Thanks.
     
  14. InSides

    InSides pfm Member

    To echo what was already said - you could 'force' any tonearm to accept a SPU (provided it has a bayonet mounting collar). However, you are in effect disrupting the design equilibrium and bringing up undue stress on the bearing structure and general operation of the tonearm.

    I would stick with the suggestions here - there are very good examples of 3012 for not too high of a price, and the maintenance of said tonearms is not at all difficult - in addition to the plethora mentioned new tonearms one could attain currently.
     
  15. Nagraboy

    Nagraboy How’d all these people get in my room?

    @InSides

    I read today in an article about arms for SPUs that the SME 3012 has the wrong geometry for G-style SPUs.
     
  16. montesquieu

    montesquieu pfm Member

    Strictly speaking that's correct - the nominally stated spindle to pivot distance (which varies anyway from version to version) puts the stylus in the wrong place when the SPU's arm collet to stylus tip of 52mm is taken into account ... you can use the sliding base to position it better but the geometry is never going to be quite correct as you can't vary the offset angle, or (obviously) twist the cartridge in the headshell. Most people find it ok to live with though. In practice, all arm setup is a compromise.

    Very few arms have their geometry specifically set up for an SPU, Ortofon obviously is, also Thomas Schick, I believe, though I had mine over 12 years ago so I can't remember the specifics. Most Japanese tonearms are aligned for a collet to tip distance of 50mm.

    @daytona600 any info on the geometry of the Project?
     
  17. InSides

    InSides pfm Member

    Somewhat true, however...

    ...problem is that various SPU models vary between 50 and 52mm.

    This states 52mm:

    https://www.ortofon.com/support/support-hifi/cartridges-dimensions-chart/

    But this earlier drawing states 51mm:

    [​IMG]

    Also, SME 3012s varied in alignment geometry between Stevenson and Lofgren. So there is that also to complicate things.

    Fun, no?

    Ultimately, as @montesquieu states - arm setup is always a combination of compromises - SME designed the sliding base to, among other things, aid the negation of mounting hole location issues.
     
  18. Nagraboy

    Nagraboy How’d all these people get in my room?

  19. InSides

    InSides pfm Member

    I always come back to "How I Learned to Stop Worrying and Love the Bomb" as an adage to live by.

    At least when hifi is concerned.
     
  20. daytona600

    daytona600 Registered User

    Single-Pivot 12'' Tonearm
    The new tonearm is a genuine Pro-Ject design and allows stepless, "on-the-fly" VTA and mounting distance settings. With its wide range of adjustment possibilities and the number of included counterweights, 100% of performance can be extracted out of any cartridge.

    Technical Specifications
    Effective tonearm lenght in mm (from the tonearm pivot to the stylus) 304.8
    Mounting distance (from the tonearm pivot to the spindle) 291.6
    Offset angle (between a groove and the stylus direction) 18°
    Overhang in mm (from the spindle to the stylus) 13.2
    Effective tonearm mass in grams 17,2 18,5 19,5 (including Alu headshell) 19.5
    Counterweight rotation diameter in mm 77
    Cartridge weight range in grams 5-23 5-25 5-25 (depending on individual headshell weight) 5-25

    [​IMG]
     

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