Direct drive vs belt vs rim vs idler arm

Dear Dover, There you go again. Trying to "prove" that one drive system is "better" than another (or in this case, "worse") by arguing from first principles. First, I think there are a lot of holes in your arguments, and second, have we, or at least most of us, not agreed that execution is paramount? That each drive system has its failings?

By now I get it; you don't like direct-drive. You do like your Final Audio TT. Live and let live.

On terminology: Motor "slip" is a term I have only read in connection with induction motors. They must slip in order to generate torque. This would apply only to idlers, as the older idlers are the only TT's I know of that used induction type motors. Induction motor combined with eddy current or other type of "braking" can make for excellent speed stability. Also, "jitter" has a specific meaning in terms of digital to analog conversion. Let's not confuse matters further by using it to describe a phenomenon related to what? Cogging or servo correction? These two phenomena are entirely separate and independent of one another, and yet they are being lumped.

FWIW, The top end Denon DD's used 3-phase AC synchronous motors. The top end Technics DD's use what you would call DC motors. But Bill Thalmann told me in conversation that if you look at the actual circuit of the Technics, the distinction between the two is not so great. DC motors are used in some of the most expensive BD turntables, as well, and the manufacturer's tout the fact.

Hi Richard

02-02-13: Richardkrebs
Ct0517
Re the Bear that tries too hard.
He doesn't have to been so stressed.
I can help him relax.

Big smile when I read that. Thanks.
In the “bear room” when they are happy; I am happy.
They are picky about the type of honey they like. :^)

SP10MKII - Not being an electronics engineer I always attributed the phenomena to cogging, or the servo having to keep speed (always a little high or low) in order to stay at speed ? Your posts have shed new light on this. Dovers last posts :^) again raise a number of points. What is it about audiophiles from New Zealand? A competitive bunch.

To improve the SP10MKII based solely on what I hear I always thought;
A little less speed correction if possible - but enough to just keep it stable?

As an owner of one I will be interested to hear/read about any direct comparisons between SP10MKII’s and MKIII’s, which have your mod. Does the gap get closed? The SP10 is still my PET project, self pride is involved and I continue to learn from her.
Cheers Chris

I guess the propensity to assign cause and effect without data to connect the two is inherent in human nature. This is why we have... religion. Because one knows there is a servo in action, and because one hears a coloration - this is not enough information to say that the servo causes said coloration. I think I know what coloration it is you are talking about vis the SP10 Mk2; I heard it too. I found that it can be ameliorated or aggravated by the choice of plinth. So, how could the choice of plinth influence servo action? Maybe there is a way that could happen, but one has to test it before jumping to conclusions about cause and effect. Plus, we have the (correct) testimony of Richard that the servo does not operate like a full "on", full "off" switch, which might indeed lead to a kind of incoherency. The servo is more sophisticated than you (and certainly Dover) think. Yet despite what Richard wrote a few weeks ago, we have reverted to talking about servo mechanisms as if they are nothing more than on/off switches.

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. The carbon fiber Grand Prix Audio Monaco uses a very advanced mega-fast modern state of the art speed correction system, yet it is not widely loved. Why is the SP10 Mk3 very much more natural sounding to my ears compared to the Mk2, if this is only about servo problems? (I don't imagine there are major differences in servo design between the two, but maybe.)

Not picking on you Dover but you talk about digitized sound from DD motors because of there electronics..but you dismiss the FACT that your Final vinyl TT uses some kind of sine wave generator so it does not rely on the line freq stability but hmmmm lets see what kinda electronics could or would they imply in practice?! Quartz oscillator? feed back?! etc. you get the point..lot more to understand before we/YOU can come to a "more better" conclusion

kind regards

Lawrence
Fidelity Forward

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.