Direct Drive

Thanks for agreeing with me, T9, but my point was not that the TT is most important; it was that flippant generalizations, like “differences between turntables…” are not helpful and may be misleading. And of course you can’t leave out the tonearm.

“Differences between turntables often comes down to the cartridge.”  The same cartridge will sound different in a different tonearm on a different turntable.  The same turntable will sound different with a different tonearm and cartridge.  These variables are not trivial. And your general statement leaves out the tonearm entirely.

Clear thinker, At least keep your prejudices vis a vis DD turntables straight.  The phenomenon you describe and object to is not at all analogous to “cogging”. Cogging is an issue for all iron core motors; look it up on Youtube. Arguably the coreless motors used in some of the finest DD turntables do not exhibit cogging at all. You are objecting to the action of the servo mechanism to maintain constant speed.  That is not related to cogging.  On the other hand, most modern high end BD turntables incorporate some sort of mechanism often involving servo control of speed, to the same beneficial end. A few posts up this page, you can find Mijostyn bragging about what is essentially feedback/servo speed control of his SOTA Cosmos.  I use the same devices made by Phoenix Engineering for my Lenco; the improvement is very noticeable and I would not be without. 

"the presence of a large oscillating magnetic device right under a very sensitive magnetic device."  You're talking about the potential for EMI from the motor affecting the cartridge.  Why not just say it that way?  As I have mentioned many times, the platter is an effective shield vs EMI, in a well designed DD.  In addition, for DD turntables that use coreless motors, the coreless motors used are all fathered by the original Dual-designed coreless motor, which looks much like a discus used in track and field.  In latter day iterations of that motor, the works are encased in a metal that serves also as a shield and furthermore the radiation from that design is laterally, not in the up/down direction.  The proof of the pudding is in measuring EMI at the platter surface while the turntable is operating.  I've done that. To the level of sensitivity of my meter, nothing is seen above background.

Ketchup, I take the bearing as a given for any turntable of any type.  So there is no special problem of a bearing in a DD type.  All platters ride on some sort of bearing.

Mijostyn, I don't know precisely how a Cosmos is constructed, but I do know that  SOTA have improved upon basic design of a suspended BD.  When you mention a "separate platform" for the motor, it must nevertheless be either suspended along with the bearing and platter or fixed in space.  Which is it? How is the platform isolated from the subchassis or shelf?  I'm just curious, not contentious.

You wrote, "Above that frequency such as at pulley speed all vibration is absorbed by the belt. Nothing gets to the platter."  Come on.  Nothing designed by men is that perfect.  The belt is a filter with a certain cut off frequency and rate of attenuation of mechanical energy.

Whatever Harry Weisfeld wrote on Audiokarma, it cannot be accessed unless one is registered over there.

Sunnydas1, what is your point? In a direct drive turntable, you can think of the platter as the rotor part of a typical motor.  As in a classical motor, the rotor is driven by the stator due to electromagnetic interaction.  Nothing physically touches the rotor (in this case, synonymous with the platter) in a motor.

I owe Mijo an apology. He referenced the STST because  it is DD (and apparently suspended). So he was not being disloyal to his favorite suspended BD turntables, SOTA or Helix.

Mijostyn, Have you fallen out of love with the Dohmann Helix? Also, you can add a Herzan or Minus K shelf to any non-suspended turntable and be better off than with any spring-suspended turntable, BD or not, because all spring-suspended BD turntables have to face the dilemma of what to do with the motor. If the motor is not also suspended, then you have the susceptibility to belt stretch when the suspension flexes. Belt stretching causes speed irregularity. If the motor IS suspended along with the bearing and platter, then you are not isolating the bearing/platter from motor vibration, except via the energy absorption afforded by the belt itself. For the belt to dissipate vibration from the motor it must be at least somewhat compliant. To the degree that the belt is compliant, then you have the possibility for "belt creep". And the beat goes on.

Terry, I am well aware of the assumptions we make when we speak of turntable speed and its accuracy or lack of accuracy. But if you categorically prefer BD turntables, with or especially without a dedicated motor controller, it’s not because BD turntables are more speed constant than a well designed and constructed DD turntable, in my opinion. And I assume your experience is limited to a few examples of each type, as is mine.

Terry, amidst all the verbiage and math, are you saying you heard an SP10R and it was noisy even compared to older Technics DD turntables? Or what are you saying?

By the way, JP Jones analysis took into account and measured speed changes over very short time intervals.

I have to take issue with Bliss, who wrote, "There are some incredible direct drives, but their notoriety was largely due to motor noise and vibration."  I don't mean to pick on Bliss, but his statement is often the mantra for those who don't care for DD turntables.  It's just plain wrong. There is no mechanical noise or vibration added by virtue of the DD technology.  In DD turntables, the platter either is the rotor or is firmly attached to the rotor of the drive motor.  The drive force is electromagnetic between the rotor and the stator.  Nothing touches the spindle or the bearing or the platter that does not also touch the spindle/bearing/platter of any other type of turntable.  What CAN be an issue with DD turntables is EMI or electrical noise generated due to radiation from the motor.  In 99% of decent DD turntables, EMI is shielded from the cartridge by the platter itself, which is usually made of stainless steel or aluminum or some alloy of copper. In fact, of course, both BD and idler type turntables have a greater potential to transmit mechanical noise from the motor to the bearing or platter, because both require a mechanical interface between the platter and the driver.

Dover, With respect I must also disagree with your persisting claim that the servo systems of "vintage" DD turntables, designed usually in the late 70s or early 80s are so primitive as to cause audible`distortions due to speed corrections mandated by those circuits.  First, most modern BD turntables wouldn't be caught dead without a motor controller of some sort, with or without feedback, to maintain constant speed.  And I for one have consistently heard the benefit of those devices if designed well, on the performance of one or another BD turntable.  Second, a skilled engineer, JP Jones, has graphed the speed stability of a brand new Technics SP10R, which I think we can agree would incorporate the most modern devices and moreover uses a coreless motor, vs a fully tweaked SP10 Mk3.  JP found no detectable difference in the speed constancy of these two turntables when he monitored them over time in a way that would reveal momentary peaks and troughs in speed, if such were present in the Mk3.

I am not saying anything is perfect, and I certainly have heard BD and idler turntables that I much admire, but if you categorically dislike DD turntables, find other reasons.  Most likely, it's EMI, in which case that reflects poor design or construction of the platter.

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