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Direct drive/rim drive/idler drive vs. belt drive?

O.K. here is one for all the physics majors and engineers.

Does a high mass platter being belt driven offer the same steady inertia/speed as a direct drive or idler drive?
Is the lack of torque in the belt drive motor compensated for by the high mass platter. Object in motion stays in motion etc. Or are there other factors to take into consideration?
I am considering building up a Garrard 301 or Technics SP10, but is it all nonsense about the advantage of torque.
I am aware that the plinths on these tables can make a huge difference, I've got that covered.
My other options would be SME20 or Basis 2500 of Kuzma Stogi Reference etc.
If I have misstated some technical word, please avert your eyes. I don't want a lecture on semantics, I think everyone knows what I mean.
Thanks in advance.
mrmatt

Showing 3 responses by johnnyb53

johnnyb53
3,510 posts
 
08-01-09: Quiddity
...the torque numbers by themselves prove ... that the argument over motor torque does not provide a key to the sound of an idler table vs belt drive.

That variable being eliminated, we can now ask "what other characteristics of these tables may result in the sound we hear?"

I nominate two for discussion: the very small degree of mechanical creep in the idler transmission and the very high reflected inertia of the typical idler motor. Which is more important? I don't know. Yet.
I nominate a third: how the drive system reacts to stylus drag. A drive with an elastic belt could stretch and recover when it encounters greater stylus drag from transients, where an idler drive or quartz-regulated DD might power right through them.

After all, there are belt drive enthusiasts who replace their stretchy belts with mylar tape or dental floss.

And VPI offers a rim drive. Reviews I've read consistently praise it for more realistic presentation of transients and rhythm.
johnnyb53
3,510 posts
 
08-02-09: Axelwahl
PS: by the way, I just like how SME tts go about it, a belt drive with dynamics! -- that's why I got one :-)
For a long time the SMEs were the only belt drives I'd heard that don't mute transients and artificially "relax" the musc. Fortunately, now the Ayre/DPS turntable creates the same sensation for significantly less money. I'm not saying it's as "good" as a $30K SME, but if that's the sound you like and can't spring for a SME, look into the Ayre.
johnnyb53
3,510 posts
 

08-01-09: Quiddity
Johnny

... The maximal velocity variation for a given length change is the product of the radial displacement produced by the length change and the corner frequency of the filter system expressed in radians per second. The numbers come out in the parts per million range.
How long is the initial transient of a piano note, a string pluck, a drum or cymbal hit? I suspect the initial dynamic jump is well under 1 ms. How large, physically on average, is such a transient "bump" in a record groove that is 1400' long for a 20-minute side? If belt drive flex lengthened that transient by 10-20%, it seems to me we would be talking about parts per million from one standpoint, but possibly a quite audible 15% variation from another.
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