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

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.

Albert,

I may get into trouble here, but I am increasingly convinced that the micro-dynamics of analog playback, in particular, hinge partly on things we have yet to measure. I thought I had built a great turntable, but somehow I inadvertently improved the dynamics of it without trying by implementing a change to make assembly easier. We may have figured out a lot about audio, but I really believe there are still volumes left out there for us to discover. I suppose the goal should be not to know everything, but to not know as little as the competition...assuming it is about competition, and I'm not so sure that that should be the end goal. Me? I'll settle for good sounding no matter where it originates. :)

Albert that's not strange at all when you look at the way Technics implemented their servo drives.

They drive the motor coils with single ended amplifiers using capacitive coupling to block the inevitable DC offset. Any such amplifier is very sensitive to the quality of the coupling cap used because it is in series with the motor coil. If the impedance of the cap increases, as it inevitably will with age, the drive available to the motor drops which will in turn reduce the forward slew rate.

I agree that there are a lot of things going on with the various drive mechanisms. Where we might disagree is with your implication that this means they cannot be adequately analysed. The reason I was dismissive of the parts per million difference due to belt stretch is that the belt creep is around 1000 times larger, so there's no point in worrying about belt stretch - by the time you fix the creep problem the stretch problem is gone as well.

Mark Kelly

I was thinking about the SL1200 series - the SP10s used push pull pairs on a dual rail power supply. Since there is no coupling capacitor it can't be the problem but it is still the case that the amplifier will be sensitive to the quality of its power supply.