Direct drive vs belt vs rim vs idler arm

Lewm, Lawrence
Could I ask you respectfully to reread my post.

My post addresses some points made in earlier posts about "motor slip" and "speed correction systems/servos", both of which can be present in any type of turntable or motor.

AC motors have been used in Belt Drive,Direct Drive & Idler
DC motors have been used in Belt Drive,Direct Drive & Idler
Furthermore there are many variants of both AC & DC motors.

Speed correction systems have been used in both Belt Drive and Direct Drive.
Speed correction systems have been used in both AC & DC motor applications.

I use those particular TT's mentioned as examples because I know them and know what type of motor they use.

Ct0517 wanted to know more about speed controllers & servos.

My post tries to explain that most speed correction feedback loops would include the following parameters - Rise Time, Overshoot, Settling Time, Steady state error, Stability - and any solution has to be a compromise between these parameters.

The question is " Do the issues inherent in speed correction/servo loops outweigh the benefits ? "
The correct answer is "We dont know".
Why ?
Because nobody has quantified the error versus the errors generated in correcting the error.

Tonywinsc,

In answer to your question, it's my opinion that it could be any of those things you mention. If I heard it, I might be able to tell, but it's impossible to say from here. It is too bad you don't have the luxury of trying several tables, arms, etc. in your system. Then, you might be able to make a determination. It could be the record, you know?

What about the latest megabuck DD turntables? I think the one from the Northwest (NVS) does not use servo correction. Is it free of the sort of coloration we are talking about? Rumor has it that it does not pass the Timeline test.

From the Wave Kinetics website
Speed Control
Capable of both 33 1/3 and 45 RPM
Utilizes a laboratory grade motor control system
High inertia platter
Speed accuracy to 1 part per 1000000
Direct drive system
Tuning optimized using a 17 degree of freedom tuning model

In linear regression the degrees of freedom is the number of estimated predictors. Degrees of freedom is often used to quantify the model complexity of a statistical modeling procedure.
This tells me that they have sophisticated speed control programmed into their speed controller based on the prediction of errors ( see my post of 02-02-13 where I explained how the algorithms are derived ).

17 degrees of freedom does not mean 17 parameters either - I can send you the linear regression mathematics behind this statement if you like.
It tends to suggest that their programs are using statistical analysis, and a continuous shrinkage technique to improve the prediction of error on the fly.
In other words, the input parameters for the speed correction/servos are not set in concrete, as in the old days, they are calculated on the fly.

As suggested in my earlier comments on the age of the Technics SP10 circuitry, these folk are using much greater computer power and new thinking on statistical prediction that is now available.

Caveat : Just so everyone is clear - I make no comment on how this turntable might sound and I am ambivalent as to the drive mechanism used.

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.