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

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.

Johnny

The net effect of the belt stretch is that it causes creep over the drive pulley, so we are talking about the same thing.

The direct effect which you postulate is reduced by the second order low pass filter formed by the belt / platter combination. 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.

Mosin

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. ;)

The Garrard I heard was running on European settings with the Loricraft motor controller. Sounded very good, with strong drive and energy to plow through difficult passages.

Quiddity

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.

I can't speak about technology that has not yet been created, I can't even speak about every turntable made as I have not heard them all. I have heard tens of dozens of belt drives and all the things discussed here at Audiogon matter (suspension, belt, arm, cartridge, isolation, etc). but there remains one overall character and that is lack of drive. You have to live with each for awhile to understand. I'm not saying all rim drives are perfect nor all belt drives faulty, I'm saying they tend to exhibit qualities or personality, much like we attribute to tubes versus transistors.

Quiddity

The direct effect which you postulate is reduced by the second order low pass filter formed by the belt / platter combination. 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.

You want to hear a really strange story? I have two identical Technics SP10 MK3 turntables. One was sent to a tech who is considered to be one of the best in the USA. He replaced all the caps, diodes and rectifiers and upon return (even though it tested the same) it KILLED the table with no upgrades.

There has to be a lot of complicated things going on with "drive" and "speed" of these various tables because the start, stop, accuracy and drive can be drastically improved by things like this upgrade and I don't know if those are even in the parts per million.