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

Axelwahl

I don't have enough information to make an informed judgement about the SME's controller implementation.

Mark Kelly

Hiho, for the record, the Empire does not go off speed if properly serviced, and can be expected, once serviced, to run for years without further attention. I have seen the motor angle being so poorly set that the belt engages the wrong part of the motor spindle, and I have seen motor spindles so dirty that the diameter was increased. The actual spec of the stock machine is impressive- well within the specs set by the best of the DD machines.

Lew, I don't know all of what Warren put in his mat, but I understand it contains an aluminum disk, and there is a thin Sorbathane layer where the mat meets the platter, so the material is not amorphous.

Although it is by far the best mat that I have heard, it is obvious that it could be a lot better- otherwise damping the platter would not have the rather obvious improvement that it does! OTOH it might be that the best we can hope for is a platter pad that can do what I said- have the hardness of vinyl so maximum vibration transfer without reflection is achieved, and otherwise maximum deadness.

I don't know about the benefits of achieving maximum "deadness". I've run some informal experiments using different damping materials on my TT's plinth. I definitely found thet there is a point where there is too much deadening which sucks the life out of the music. Yes, you have to address gross vibrations and such, that's not what I'm talking about. AFTER you have got is pretty right this is the fine tuning. Just don't over do it.

Bob

All,

I just caught on to this thread and need to find the time to digest it in its entirety before replying, but one thing jumped out at me as I was scanning through it - Axle's comment (quoted below). I'm not singling you out Axel. It's just that your clear writing called my attention to it.

Axelwahl wrote:
The platter material / mats / pads / and other damping are ALL colouration items (excluding some really heavy lead-loaded mats adding more mass)

I contend (as Ralph does) that a compromise in dynamics is a coloration, and if dynamics are unconstrained, then you are more faithful to the music.

As far as mats and other materials are concerned, I subscribe to the following position. A part of the job of the various components in an analog rig is to transmit (as opposed to reflect) vibration down the chain at EACH and EVERY materials interface.

A mat is just one more part of a turntable - whether supplied by the manufacturer or purchased in the aftermarket. It either "works" or it doesn't. It adds another interface to the equation.

Examples of interfaces are:

- cartridge to tonearm
- tonearm to base
- record to platter
- platter to bearing
- bearing to base
- base to stand

and so forth ... until we work to the Earth's core, the sun burns out, and life as we know it ceases to exist (grin).

Material selection is critical here, with one consideration being to match the relative speeds of sound of the interfacing material pairs.

Think of how a flat stone can be thrown so that it either skips across a lake or alternatively passes immediately into the water.

There's much more to this, but I don't have the time to explore it at the moment.

I'm deep in the throes of supporting Mark's controller design, but I'll try to find the time to read this thread from start to finish.

Cheers,
Thom @ Galibier

I would just like to add my five-penneth.

Aren't the idler wheel and belt drive systems completely differing technologies/sciences? On the one hand (Belt) you have a large mass in rotation, a motor that only really pushes when the platter slows, and a flexible drive system (belt). One the other (idler) you have a clamp sytem where the idler wheel (inside rim) pushes the platter away from the centre bearing or (outside) pushes the platter towards the bearing. The platter is trapped between the bearing and the idler. (Depending where you are standing both idler types are the same.)

I don't see how a comparison can be made. They are just different and both work well or badly depending how well they are engineered and built.

:-)