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

Oops

I looked at the wrong motor on the Hurst table, the actual motor used by VPI is the lower torque model so the figures are 16mNm at the shaft and 290mNm at the platter respectively.

This would seem to favour the Garrard but only if you find a 10% speed reduction acceptable. If you want the Garrard to slow by a lesser amount (say 1%) the useable torque drops almost proportionally - at 1% the torque is about 1mNm at the shaft, say 50 mNm at the platter.

Mark Kelly

All this technical discussion reminds me of the numbers war in electronics in the 1980s. If we are to believe any of those specifications the Yamaha receiver is a much better performer than a Lamm.

I began with rim drive over 40 years ago and was talked into a belt drive, assured of it's superiority by the Thorens rep himself.

I owned tens of dozens of belt drives and each sounded different but not until I returned to rim drive / direct drive did I get the immediacy and impact that had been missing all these years.

I clump rim drive and (good) direct drive into the same category as both provide similar sound.

Quiddity, I don't know where you heard a Garrard or other rim drive that had such poor speed results, but in a side by side test against three of the finest belt drive tables on earth the Garrard was top or very near.

Albert,

Mark makes the controller for my Saskia idler drive, and I can say firsthand that he looks at things from a critically analytical viewpoint. That said, he owns idlers including the Garrard 301, Commonwealth and others, and he can fix the speed on pretty much anything. Basically, he may be saying that the Garrard needs a good speed control. ;)

Best,
Win

Albert

I measured those results in my lab on a Garrard motor I know is in good working order. I have also measured several other motors used in idlers and found very similar results. Since the results accord with the theoretical results expected from these designs I have no reason to suspect that they are anything but typical.

You are correct in saying that the torque numbers by themselves prove nothing, with one exception: they 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 have designed a belt drive which has a very, very low level of creep. It is in the process of being built and will be on show at RMAF in the Galibier room if we get it finished in time. I do not expect it to sound like an idler table, I expect it to sound like a belt drive with the belt creep problems removed.

The drive design allows for the addition of a high speed inertial system. I expect that if this system were added the sound would change; it remains to be seen exactly what this change is and whether it is seen as a benefit. The inertial system is still on the drawing board, it will not be at RMAF.

One of the problems is that the "donor table" has inevitably been designed to perform with a different drive system. Accordingly I've asked Thom to audition the drive on his lowest model table on the grounds that this has had the least attention given to optimising the synergy between the drive and the other mechanicals.

Mark Kelly

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.