As a (biological) scientist myself, I think that "what we have here is a failure to communicate", to quote the chain gang boss in "Cool Hand Luke". Motors and motor controller technology have their own jargon that tends to mystify those who have not been formally educated in the respective disciplines. (I am reminded of some smart friends of mine who complained they did not understand even the title of one of my published papers, when they took it upon themselves to look it up.) I sometimes feel as they did, when I read about motors and motor controllers, for example, one or two of your posts on this thread. Moreover, I can grasp the meanings eventually by googling some of the more obscure terminology, but I tend to forget the fine points, in between discussions such as this. Therefore, I have to be content with generalities drawn from your posts (Phoenix) and those of a very few others who really understand this stuff. And then I have to take refuge in my own listening experiences. Like you said, we each will hear differently. ML is using state of the art turntables, in my opinion, so it doesn't really matter. I readily believe his testimony. By the same token, I really value your posts as a basis for my own further education in this area, Phoenix, and I would not like to see you leave this forum. Keep stretching our knowledge base, by all means.
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Pursuant to mijostyn's concern about an "oscillating magnetic device" under his LOMC, I do believe in fact that in some designs one can hear an issue, faintly. I have guessed that EMI from the motor may be in fact what some claim to be caused by "cogging". Coreless motors are much less prone to generate this interference, based on my listening to several different brands and models in my own home system, but still, I am guessing. If you read the L07D website, you will see that some have recommended adding some shielding under the platter to ameliorate a faint glaze with the L07D. It's not actually a problem you can hear; it's more like a problem you did not know you had, until you eliminate it. That was my experience when I added an extra bit of shielding between the motor and the underside of the platter on my L07D, per recommendations on the website. Paradoxically, the L07D uses a coreless motor. It also comes with a thick stainless steel platter sheet, which I am guessing was meant to function as a shield. The Technics SP10 Mk3, on the other hand, while it does have a massive iron core motor compared to others, has no issue I can hear. Possibly because it already has a massive and thick platter assembly that does a good job also as a shield. My old Mk2 definitely did have a kind of gray-ish coloration (two samples over 5 years or so in my home system) which could have been due either to EMI from the motor or from.... So, for any particular model of DD, there is either no problem or there is a simple and inexpensive solution to it. The trade-off in speed constancy is to my ears well worth it.
While we're at it, the Lenco idler design places a big motor under the platter as well. I guess the Garrard does to. In any case, I hear no such issue with my much modified Lenco. I would characterize its "sound" in much the same way as Mike L characterized the Saskia, albeit the Saskia is a Lenco on steroids and surely does everything better.
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The point I tried to make earlier and which seems to have been ignored by some who might favor turntables with laissez-faire speed control is that yes, live human musicians will inevitably vary tempo during the course of a performance of a given piece of music and given conductors will pace different classical pieces differently, but that's the crux of the matter. You/I want the turntable to make no alterations of tempo that might obscure the human factor inherent to the pleasure of listening. The turntable should ideally do no editorializing, in other words. Plus there is the fact that inconstancy of turntable speed affects pitch, whereas human errors in timing produce only changes in tempo. No turntable or drive system is absolutely perfect in this respect, but that should be the goal. In my opinion, of course.
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I THINK that some of us are saying this: Absolute accurate speed is not the issue. I (and whoever) would agree that I am not able to discern the difference between 33.334 and 33.333. In fact, I know for sure that I cannot tell 33.333 from a constant 33.5 or from 33.2, because I can do that experiment with the Phoenix Engineering Eagle and Roadrunner driving my Lenco motor. What IS potentially audible are VARIATIONs in constant speed, drifting of speed during musical passages especially that feature piano and/or stringed instruments. Whatever technology used in turntable design and build that eliminates or minimizes speed instability (DD, Belt-, or idler-drive) is fine with me. It just so happens that for me the best vintage Japanese DDs and my Lenco do it at lowest cost or best bang for the buck. Belt-drives at anywhere near the same cost have failed, speaking for myself.
Mijostyn, Those rumble filters may be useful if you hear rumble, but in all other cases, they are no free lunch. The filter elements color the sound all the way up the scale, inevitably. I also don't know where you are getting your LPs from, but I rarely encounter rumble that is problematic enough for me to want to engage a high pass (rumble) filter. This is using two completely different audio systems in my home environment, driven alternately by 5 different turntables. I'm not saying "never", but it's rare.
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Phoenix, Thank you for embellishing on my response to Atma-sphere re my point that operating a motor with 3-phase AC synchronicity does not per se eliminate cogging. I am a rank amateur on this subject with only a good college level background in physics (and a lifelong habit of thinking like a scientist). But I was a bit puzzled by your statement: "A 24 pole motor turns at half the speed of 12 pole motor so the frequency of the cogs is identical in both (120Hz)." In a direct-drive turntable, doesn't the motor have to turn at 33.3333 rpm, regardless of the number of poles? And therefore might there not be a theoretical advantage to having double the number of poles?
Oh, and thanks for clearing up the many ambiguous on-line websites that don't come right out and say that coreless motors are free of cogging. It makes perfect sense (and I think I hear the benefits), but you'd be surprised at how poorly this subject is addressed and explained. (Or maybe you wouldn't be surprised.)
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Ralph, In my understanding, cogging and synchronicity are two different things. Cogging is a function of the number of poles; the rotor experiences a regularly irregular rotational force due to the naturally varying intensity of the magnetic fields produced by the stator. The rotor is therefore constantly inconstant in its speed. There is a regularity to it that is said to be audible to some, and that's "cogging". The tendency can be ameliorated by using a stator with a lot of poles, the more the better. Coreless motors may do away with the issue altogether. (No matter how much I search on that last topic, I have never found a satisfactory treatise on the subject of coreless motors vis a vis cogging, but most talk about coreless motors as if they are free of it.) On the other hand, an AC synchronous motor does lock onto the line frequency, and this can keep the speed steady, absent drag, etc. But an AC synchronous motor could still exhibit cogging, if it is poorly designed with an inadequate number of poles. Maybe Richard can comment on my thoughts.
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Off-topic: Hi, Mike! Good to hear from you.
I have only one further comment: It is not valid to lump all servo speed correction mechanisms as if they were all the same. Technics was dominant in the DD industry, and they espoused powerful iron core motors driving heavy platters (if we limit ourselves to the SP10 series) and very frequent speed correcting. But other manufacturers, e.g., Kenwood in the L07D, settled on using less powerful coreless motors, to minimize or eliminate cogging, and a comparatively laissez faire approach to servo correction, which means that corrections are fewer and less frequently made. This to my ears resulted in the L07D sounding a tad more "musical" than an unmodified SP10 Mk3. Applying the Krebs mods and now the chip made by JP Jones have made my Mk3 sound a lot better. So, just to say that those designers of the 70s were well aware of trade-offs related to servo control.
In keeping with Mike's critique of the Monaco, I had wondered what became of that product given the initial ballyhoo. One problem with it, in my mind anyway, might be its relatively low mass. When speed corrections are made, there is an equal and opposite force generated at the platter such that the chassis "wants" to turn in the opposite direction from the platter. I think you need mass to overcome that manifestation of Newton's 3rd Law.
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bohe60s, You wrote, "Nice, if not perhaps irrelevant, if we can detect it audibly." Was that in reference to my post at 11:23 AM? If so, can you explain your meaning a little better? If you were referring to my post, perhaps you did not understand what I was saying. If one can detect speed irregularities (audibly, of course), then it is not irrelevant to eliminate same, so much as that is possible. But maybe that is not what you meant.
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Davey and Rodman, Wouldn't you rather leave the human-ness of live music in the hands of the actual musicians, who are also human, rather than to the super-imposed alterations in pitch and timing due to stylus drag, belt creep, and the like? For me, I want to eliminate those mechanical problems to the greatest extent possible so that the actual treatment of the music by the actual musicians gets across to me, so much as that is possible. The reproduction system has enough inherent problems as it is without admitting those others into the mix.
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Non-compliant or very low compliance belt and placing the motor drive as close as possible to the circumference of the platter are the best ways to minimize belt creep. Of course, a truly non-compliant belt would not bend around the platter. But tape is an excellent choice.
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