Turntable upgrade recommendations: SME vs AMG vs Technics vs other

@terry9 , I do not think Raul is talking about the platter itself ringing. He is talking about the suspension resonance point, the platter resonating on the air just like an automobile suspension without shocks (dampers). The heavier the plater the higher the frequency the platter will bounce at. This is unusual as normally it is the other way around but as the plater gets heavier the spring rate increases, the air gets stiffer becoming a solid wall (the thrust bearing). Platters have become a male phallic symbol. There is no reason for a platter to be heavier than about 10 lb. Heavier than 20 lb is totally unnecessary with a normal bearing. Air bearing tables just need to get the resonance frequency out of the audio range or higher than the frequency response of the best cartridges, about 70 kHz. What weight that takes I have no idea. 

Dear @drbond  : In this link go to the end of the page and downland critical information about this phono stage:

https://www.fmacoustics.com/products/phono-linearizers/fm-223/

@mijostyn

"with modern machining bearing tolerances can be very close to perfect"

Agreed. It’s the "close to" that tells the story. In the old days, bearings were machined fairly closely, and then rotated against each other in situ, with fine grit, to smooth them. The finest bearings were done with the finest grit. That’s exactly how the glass-stoppered reagent flasks from the chemistry lab were made - and they were literally air tight.

That’s also similar to how the billion dollar telescopes are made today, so I doubt that the practice can be improved upon with machining. With an air cushion, however ...

Thanks for your explanation of Raul’s point - it was opaque to me. To that point, a platter bouncing on an air column is clearly visible and audible. It can be tuned away by changing the pressure by a few psi. Ask me how I know.

Heavier than 20 lb is absolutely useful for inertia when the stylus is dragged through the groove, producing a variable retarding torque. It is also useful for resisting the irregular pulses of an electric motor, and the bearing noise in that motor.

I have tested this - with a 45kg platter, the precision 2W electric motor, run from a quadrature power supply, generates enough noise from these sources to be repeatably audible, as a slight HF glare of the CD kind. Removing the belt tells the story.

Here is a bad thing about a spring-suspended DD turntable: The energy put into rotation of the platter is also going to twist the chassis on its suspension, in the direction opposite to platter rotation (counter-clockwise). That is why it’s a good thing the Motus uses a low torque motor. Even so, the platter might end up with a very inconstant speed, due to the servo trying to correct for twisting combined with the variable effects of stylus drag on the rotation of the platter. Has anyone published a study of the speed constancy of the Motus? I am all for isolating TTs, but not with springs. As to low torque vs high torque (without defining the terms, the two statements are meaningless), torque only comes into play when the platter is starting up from rest. Once the platter is rotating at or near its set speed, torque is neither a good nor a bad thing, so long as there is enough to tweak the platter speed when called upon by the servo. What does make a difference is the "tightness" of the servo control. Different designers have adopted different levels of stringency for speed control. Technics TTs historically (I don’t know about the SP10R) adopted a very tight feedback. Other vintage DD turntables used looser servo control, especially those that also used coreless motors, like the L07D, the Pioneer Exclusive, and the Yamaha GT2000(X).

Mijostyn, Your categorical dismissal of the Lenco is silly. True, the bone stock OEM Lenco GL75 or 78 can be bested by modern turntables, but not by any belt driven turntable below the $2500 or so retail cost, provided only that the tonearm is refurbished or replaced by a better one, and highly modified Lencos that still retain the motor and the vertical idler drive mechanism would surprise you, if you ever sought out a sample to listen to. Visit Lenco Heaven to learn what can be done on a relatively limited budget with Lenco parts.

Something that Raul wrote that wasn’t "wrong" has been misinterpreted by subsequent comments. More mass per se does not result in a higher resonant frequency; it’s just the opposite. I think what Raul meant is that more platter mass on an air suspended turntable requires more work by the air suspension which could result in an increase in the absolute magnitude of the resonance. I don’t know if that’s been proven, but it makes some sense.

@lewm 

Agree with almost everything. But: a low torque motor (e.g. 2W - yeah, I know watts are joules/sec) simply lacks the torque to affect speed very much. It's barely enough to overcome stylus friction and belt flexion, so it's tiny irregular forces (noise) have little influence on a massive platter.

You note that 'tightness' of the servo is an issue. I do so agree. That's why I use an AC motor - an AC motor sets a constant pace, it doesn't try to correct the pace. The speed of an AC motor can be set very accurately and very stably with a quality power supply.