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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
clarkie's avatar
clarkie
4 posts
 
Mark: I am no expert but my experience is that the heavier the platter on the belt drive T/T the more likely we are to have less variations in speed. I owned a Michell Gyrodek for some years and always knew that its speed stability was marginal. It wasn't until I purcahsed my present Acoustic Signature Analogue One Mk 111 that I realized how bad the Gyro had been. I know that things are relative. I have to assume that both decks are well engineered within the requirements of each design. I am inclined to believe that the real reason that the AS is better is because the platter has higher mass. I am not aware of how heavy the platters are on idler T/T's but would make an educated guess that they are much less than the AS which I will use as my reference.

In the case of the idler T/T at no point is the platter allowed to rotate in a 'free' state. The idler drive is always in contact and driving, even if we admit that there IS some compliance in the rubber driving material.

I stand by my firtst statement that the two systems are completely different and both can work or fail. It's really only about engineering.

Clarkie
axelwahl
788 posts
 
Hiho,
well, well, well.

What you seem to overlook is the reality of it all. Just have a look at HOW MANY tt manufacturers use exactly that 'rubbished' approach and then ask yourself why.

I think a STABLE AC motor (not DC which is prone to drifting) is just cogging, some more, some less, even 3 phase, and so along comes the soft, long, or what ever, belt to 'fix' it. At the same time mass is added, has to be added to the platter, to counter act the soft belt drives lacking dynamic performance.
Practically ALL tt's that make the top grades (Hi-End rating > 100 points) in all known to me German Audio Magazines are designed that way.
Then a 'controller' may be added (in some cases more of the name then the real thing), at extra expense.

The question: how much does one actually hear the difference?
Point to add: it was one of these 're-worked' Garrarde's (by Loricaft) the wound up pretty much on top of the heap. It was superior DYNAMIC performance that did it to the testers... alas not the high price with some questionable suspension on squash-ball, and other sundry items.
Greetings,
quiddity
119 posts
 

Clarkie

You appear to be making two statements:

1: High mass platters improve the speed stability of belt drives

2. The transmission in an idler is stiff, so the motor is tightly coupled to the platter.

and following them with a conclusion:

3. Therefore "the two systems are completely different".

The two statements are reasonably uncontroversial, but I cannot see how they are supposed to lead to your conclusion.

The obvious implication from your statements is that belt drives are necessarily less tightly coupled than idlers and that the platter in a belt drive is somehow free to rotate in an uncontrolled manner. This is supported by a statement in your previous post where you said that a belt drive has "a motor that only really pushes when the platter slows".

This is completely wrong. If the two systems are designed to have the same drive compliance then they are by definition equally tightly coupled. There is nothing to prevent this being achieved in practice; that it has not been seen as a desireable goal by the designers is an historical artefact, not a matter of physical necessity.

Axelwahl

you have confused the terms slip and creep in my post. They are not the same thing.

Mark Kelly


quiddity
119 posts
 
Sorry that last part was measnt to be for Hiho not Axelwahl.
hiho
451 posts
 
.
Axelwhal,

Just because many so called "high end" - a relative and useless term to me - turntable manufacturers use soft rubber belt does not make it right or enough to overwhelm alternatives. These days turntable manufacturing is a cottage industry, compromise has to be made for ease of production. By the way, what exactly is your question or point, as you seem to reinforce what I said in my last post? I personally do not subscribe to heavy heavy weight approach as it will reach a point of diminishing return. I rather have a better stronger motor to get the dynamic I want than to get it from a high mass platter. To me direct-drive is the most elegant approach or belt-drive with non-compliant material or idler-drive with a quieter motor. Basically, all three drive systems can sound good with different approaches to compensate their inherent problems. That's why is called engineering, isn't it?

The Monaco turntable is the most desirable turntable for me if I can afford it as it suits me from a technical and aesthetic standpoint. It's elegant. I haven't heard the sound but I have a feeling I will like it.

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