Direct drive vs belt vs rim vs idler arm

Dover
No inconsistency at all. I have repeatedly said that there are many paths...,
Obviously within each family of drive there is bad and good engineering design.
Further I have tried to be as generic as possible in my posts. I mentioned the Goldmund only because it gave me a first hand view of the effect of stylus drag (which was astonishing in its magnitude).No other reason. I mentioned the SP10 mk3 only because I had the moment of inertia figure for its platter and I made no comment on its goodness or otherwise. It was simply to illustrate what moment of inertia meant and to quantify it.
I am quite familiar with the LO7 D, it is indeed a well built machine.

The discussion on arms carts etc is spurious as it is outside the realm of this thread. I agree they have an effect on perceived speed stability and that they place different demands on the TT and its drive, but what we need is a platform that is speed stable in the first instance.
We are talking about drive methods and their various features and failings. They all have failings, hence my comment re the type, that in the opinion of the listener is the most innocuous.

"The perfect TT has absolute speed stability under all load conditions".
I have also been consistent that in my view that a well designed closed loop speed control is required if we are to approach this goal. This regardless of the drive method employed, the platters moment of inertia, motor self correction characteristics or its torque curve.
While technical specs are limited, the TechDas TT ( a refreshing take on TT design) .with a platter approaching 30 kg and a high moment of inertia. With a synchronous AC motor and belt drive....Appears to have closed loop speed control.
If this is so, it seems that I am not alone in this view and that the the designer considers these small changes in speed to be musically important.

Dover... great writing and I can agree with most of what you wrote...

Robert fulton did do testing and experiments and of course most important listening ...his conclusions where that hi profile line contact elliptical ect etc... in a pivoted arm causes "lots" of distortion (audible)due to the fact of cantilever twisting...and in fact maybe do to hi freq phase anomalies because of the twisting

moreover you maybe right on why we hear differences in everything because of the servo/drive/electronics etc..

please carry on

Lawrence

Fidelity Forward

Peterayer...Yes i totally agree if it was not for a lot of people on these forums starting to demand better performance then no company would be willing to invest in our little hobbies!

Manufactures do read the forums!

Lawrence
Fidelity Forward

Dear Dover, That was a nice post. But as regards your "old" Sota Star, I had a different experience with my old SOTA Star Sapphire Series III. I owned it from about 1990 to the late 1990s. This was the turntable that made me a believer in the potential deficiencies of belt drive. I could easily hear the pitch instability, particularly on jazz and classical piano LPs. For all that time, I put up with it, because I thought that the distortion I was hearing was on the master tape from which the LPs were made. (There was no internet in those years to tell me I was wrong.) Then I bought a Nottingham Hyperspace, which is not too different from the SS in design philosophy but is worlds better in its accuracy of reproduction of piano music, i.e., pitch stable, elastic belt drive notwithstanding. When I added a Walker Precision Motor Controller to the Hyperspace rig, everything went up a notch further; the Walker made a huge improvement in what I already liked quite a bit. These experiences led me to begin to appreciate the importance of drive mechanisms and the proper job of a turntable. I hasten to add that, from what I have gleaned second hand, the modern SOTA turntables are also much improved over my old Star Sapphire. I mean no slur on their current products.

Yes, the modern Sota uses an AC motor and electronic power supply in lieu of the previous DC motor. My Cosmos IV seems dead on, and since the motor is mounted to the same suspended sub assembly as the platter and arm, there is no movement between them, unlike most suspended tables where the motor is fixed and the platter/arm is suspended.

Still no comment on my interpretation of the Fat Bob's video after dropping the cartridge?