Turnable database with TimeLine

Hi Halcro, let me explain something about motors here without the added detail of charts and graphs. A motor runs at a constant speed to the casual observer; but if you take a much closer look you would see that the motor armature actually speeds up and slows down as it passes by the individual poles. Cogging is an accentuated aspect of this motor property. A flywheel is added to the armature to smooth out this periodic motion. This is a property of any motor type. Now, with the exception of DD turntables, the motor is just one part of the platter drivetrain. If the pulley on the motor shaft, or the idler as the case may be, is not perfectly centered then the pulley will add a periodic motion. The roundness of the pulley and of the platter where the belt or idler rides as well as the eccentricity of the platter contributes to this periodic motion. So just like a record that has an off center hole moves back and forth during play, the motor pulley and platter are doing this too; but hopefully at an almost undetectable amount. Therefore, the motion of the platter- any platter is not perfectly constant during a single rotation. Being periodic, meaning that it slows down and speeds up, it can still hit the 1.8 second mark every time because the average speed is 33 1/3. You can see an eccentric record moving back and forth during rotation causing the tangential speed at the stylus to vary. The record is still spinning at exactly 33 1/3; but if it is off by a good amount then the WOW can be heard at every peak of rotation. That goes back to my motor analogy- you can speed up and slow down your car between mile markers and still have the correct average speed.

One other thing: Look at the specs of most turntables. The WOW & Flutter measurements of most high end tables all seem to be around +/-0.02% to +/-0.04%. Most of these very nice turntables here are showing excellent speed settings to within 0.00X%. It's clear that many companies have come very close to perfection with regard to speed control. WOW & Flutter numbers do not seem to vary much among competitive tables which is I believe due to limits of machining tolerances. WOW & Flutter being the periodic motion of the platter that I described.

Thanks Halcro. As a fellow Raven user I appreciate your feedback. I have a strobe disc that allows active adjustment while playing so I'll add a small amount of compensation.
Best regards,

I was reading over some email exchanges that Mark Kelly and have had, and some things were discussed that are useful to know when it comes to motors.

An interesting point is that a dead quiet, high torque motor might be an awful choice in a turntable application.

A motor is not necessarily better just because it has a lot of torque for its size. Some manufacturers increase stator iron, so they can improve torque numbers, but cogging is often dramatically increased as a result. One very famous maker uses such a motor, probably because of its low cost. I suspect it might pass the Timeline test, regardless. Still, that doesn't mean the product is as good as most consumers are led to believe, although an astute listener can hear it.

Can one obtain a cogless motor? Yes, but the form factor is too small to use in a turntable. There are three-phase motors in some computer drives that exhibit virtually zero cogging. Unfortunately, the technology hasn't been applied to motors of a suitable size for our use.

Fortunately, good motors are to be found, or made. Continuum uses a custom motor that cogs very little, for example. I use another that suits the purpose very well, and some other manufacturers use motors that are excellent for their designs. With some makes there is no rhyme or reason, however. They just copy someone else without knowing why. I am convinced that happens.

My point is that knowing about the specific motor is useful when making these Timeline comparisons because what you see isn't always what you actually get.

Don, You (sadly) wrote:
"I am not a fan of servo controlled speed. The speed is wrong a lot of the time!
A properly designed turntable should run at a constant speed!
If there is stylus drag (that audibly effects sonics) , then increase the speed slightly." (DUH!!)

That is more of a rant than a rational statement. It reflects your complete misunderstanding of the problems associated with maintaining constant platter speed despite frictional forces (stylus drag) that are constantly changing in magnitude. I take it your experience with direct-drive turntables, if you've had any, has been a negative one. In reaction, you are creating a hypothesis based on no data and a paucity of knowledge. You may fairly say that you dislike this or that direct-drive turntable, but do not presume that your subjective opinions are necessarily applicable to all such turntables. Nor do you have any data that would lead you to understand why you did not like whatever you've heard.

About the SDS (and similar motor contollers) I agree with you. Any belt-drive tt motor that does not have a built-in motor controller circuit of some sort will benefit greatly from the addition of a motor controller designed to maximize the performance of the particular motor type. For example, a 3-phase AC motor is quite a different animal from the induction type motors used on early Garrards and Lenco. The SDS (and the Walker Audio Precision Motor Controller) work on a wide variety of motor types, but for the same reason neither is optimized for any one type.

Someone else brought this up, and it puzzles me too: Why the heck does the Timeline laser flash 8 (or 6) times per revolution, when we are only observing a single flashpoint at a time? What is the advantage? I had hoped incorrectly that the "extra" flash events were used to enhance the sensitivity of the instrument. (As I stated, if 6 flashes could be used to cut down the time interval between observations from about 1.8 sec to 0.3 sec, then the sensitivity begins to approach that of a continuous read-out, to make Tony more happy with it. But as others, including Tony, point out, this is not happening.)

Since the mass of the Timeline is concentrated over the bearing, giving the motor lots of mechanical advantage in moving it, and since the Timeline that I had use of is very reasonable in mass, less in fact than many record weights, it's hard to imagine that its mass would alter the results detectably. If the motor cannot handle THAT much drag, it probably cannot handle stylus drag either.