Direct drive vs belt vs rim vs idler arm

lewm I became aware of some sort of vail with three examples of the Sp10mk2. For a lack of a better discription I found it similar to that of flutter that seam to be consistently fixed into the upper top frequency's.

Dover.
We have covered servo control in depth in this thread.
I do not understand why some people are so down on this approach. It is just feedback. Sure it has to take into account inertia, complaince and torque. These very same elements are present in purely electronic feedback in the form of inductance, capacitence and gain, respectively. Yet the same people who have no problem with their amps employing feedback, criticize its use in speed control. It is the same stuff.

Ref my generic comments on local and global feedback. Of course there are variances within each family. It is all in the implementation. I am only reporting what I hear with every TT from the respective groups. With some designs its obvious, with others it is more subtle.

The Technics uses old technology. yep, That is one reason why I said on 01-05-13 that it would be great if the big companies, who originally built these models, looked at making updated gear.

As Lew said, the motors employed in say the Technics employ very similar circuits to AC synchronous motors. The rotating field voltage does not cross zero volts so it is not an AC motor but it performs in a similar way.
Further in AC and DC synchronous motors, the rotor turns at the same speed as the rotating field, only slightly behind it. Imagine a clock having two minute hands one 5 minutes behind the other. The trailing hand being the platter. They both rotate at one rev/hour. If load increases the gap will increase to say 7 minutes, but after that momentary drop off in speed the two hands will again rotate at one rev/hour. It is interesting that people have had to adjust the speed of their TTs after lowering the stylus. If there is no belt or thread slip, with synchronous motors, this speed adjustment should not be neccessary. Something else is going on.

Ct0517.
yeah I much prefer happy bears, no one wants to be in a room when they are angry.
I have a customer who has just had a MK2 upgraded after originally getting his MK3 done. It will be interesting to read his comments.

Dover, This is what I fear as I grow older: "continuous shrinkage". If you can help me avoid that, please do send the relevant information.

Oh yes, I meant to add that the gibberish you (Dover) quote from the NVS website does not really tell us for sure whether it uses a servo mechanism. Could be that they are talking about the ways in which they assure the synchronicity of an AC synchronous motor controller, to compensate for drag of any kind, stylus or otherwise. I had read from another source that they don't, in fact, use a servo.

The difference, in my mind at least, would be that a sophisticated controller for an AC synchronous motor (which may be what NVS does) would affect the motor's ability to sense that it had been slowed or pulled out of AC synch by some external force and correct for that. Whereas, a servo would require a speed sensor at the platter end that would tell the motor that the platter had deviated from the programmed speed. Then the motor fixes that by applying enough torque to overcome whatever new drag had been introduced. Both cases are a form of negative feedback. You might analogize this to the difference between local and global NFB, respectively.

(I don't much care for NFB in my power amplifier.)

Lewm,

According to the Stereophile Review of the Wave Kinetics NVS it uses a DC motor with a laboratory grade servo controller with an active ultrasonic feedback loop

Reference - Stereophile vol 35 no 10.