Vintage DD turntables. Are we living dangerously?

Dover.
I heard the Final enough times at Warwick's to get a fix on what it did well and what it did not so well. Hearing it at your place only served to confirm this.
re the amazing comment. Under the right circumstances I find my car stereo to be "amazing" . We adjust our expectations based on where we are.

Re speed stability, Your comment re DD TTs needing servos to work is immaterial. It is just a different technology that's all.

I am on record during a conversation with Lewm stating that I could not live with a standard SP10 MK3. (To my ears they have a high frequency jitter speed problem that is just plain irritating, which took me 15 years to tame.) I will now expand that statement to say that I have not heard any standard DD TT that I could live with. So perhaps Warwick and I are almost on the same page.

Could I live  with the Final? 
While I admire what it does well the, to me, obvious dynamic speed problems disqualify it from my bucket list.

As I said, we each make our choices based on our particular biases. I have no beef with anyone preferring a different TT to what I would choose. This diversity alone makes our hobby fascinating.

richardkrebs
I am on record during a conversation with Lewm stating that I could not live with a standard SP10 MK3. (To my ears they have a high frequency jitter speed problem that is just plain irritating, which took me 15 years to tame.) I will now expand that statement to say that I have not heard any standard DD TT that I could live with.

It would appear then that you agree with me now.
It is surprising that you could live with DD turntables for 20 years prior to "taming the jitter". With regards to "taming the jitter" - thats what the digital guys claim each time they release some new algorithms or technology. As I said to Lewm there is no evidence that your lead and glue mods to the SP10 reduce the number of error corrections per unit of time which is what he claimed. You may have slugged the sound but the error correction is still going on.
Servos and error corrections are not irrelevant as you claim - these are micro adjustments to the speed of the motor and platter. This is why you hear "jitter" with all direct drive turntables ( other than yours of course ).

Dover, It has long been my observation that your major goal in participating in this discussion is to "prove" by the force of insistence that your particular Final Audio turntable is "the best".  Secondary goals are to prove that the finest direct drive turntables are inferior to the finest, most expensive belt drive turntables.  You've made these points over and over again, never with any sort of "science", except for the implication that what you hear and report is to be taken as gospel.  So, I hardly think it behooves you to come down on Richard for not offering "proof".  Actually, Bill Thalmann may have made some measurements of Krebs-modded SP10s that do support the claims.  I will inquire.

It is irrelevant to me that you place no value in my subjective judgement, so we are even, so far as that is concerned. What I wrote about the Krebs mod was meant for persons who use SP10s.  Direct drive has its issues, and so does belt drive.  Apparently you prefer belt creep and speed instability to issues related to servo mechanisms.  That's fine with me.  And by the way, if your Final Audio has a motor controller drive system of some kind, the chances are that it too has an error-sensing mechanism which has the potential to produce an effect not unlike that of a DD servo.  The only difference in the case of a belt drive is that the corrections are delivered via pulling on a compliant belt, which has its own pros and cons. Playing LPs is an exercise in inexactitude; each of us must find his own set of likes and dislikes which in the end must be based on listening.  What I don't understand is why you hang around here, if the subject of this thread is so odious to you.

Lewm -
Life is a constant learning exercise, that is why I read and participate in these forums. I regularly listen to and enjoy music on all types of drive ( other than digital ). You are quite wrong on the Final - I would be disappointed if there were not a better turntable out there - because I enjoy the constant upgrade process and the joy of rediscovering old records in a new light when one accomplishes gains in the playback system. I do not claim it is the best, I simply haven’t heard anything better yet. There are many TT’s I still have not heard. The comments I have made in this thread are only related to TT’s that I have heard in depth. Ditto with Rauls MM thread - I still prefer MC’s but have gleaned much knowledge and tried a few new MM’s in the past year or two. I continue to listen to other turntables in my system - it’s enjoyable and usually learn something.
A few corrections on the Final - it has a very powerful AC motor, no active speed correction. Speed is controlled by precision oscillators regenerating sine and cosine waves and a power amplifier to drive the motor. It has separate controllers for 33 & 45 and I can set the speed between 0 & 85 rpm on each as well as vary the level of torque applied. Speed relies on inertia (26kg platter), powerful motor and AC phase locking. As regards belt creep the Final uses silk thread - the stretch is negligible compared with rubber belts, otherwise I agree with your comments on belt drives (rubber) and so far the only decks that have approached the Final have been idlers.
Speed and power wise, the most astonishing TT I have heard in the past couple of years was a Denon RP52 Idler. The owner, a DJ, demonstrated side by side with a Technics DD in the same system that you could could start and stop the Denon with a low compliance MC sitting in the groove and hear virtually no slurring of the music on start up. Doing the same test on the Technics DD resulted in much slower start up such that you could hear the music coming up to speed. I wish I had made a video of it. I suspect the EMT 927 would be in that league - huge torque coupled with a 50lb flywheel.
The Technics DD motor used for driving lathes, the SP20, was designed specifically to operate in conjunction with the Neumann 60lb flywheel and has significantly more torque and poles than the SP10mk3 - this would be an interesting DD platform to listen to.    

Dover
I have listed the time line of my upgrade development on another thread. There I outlined why I persisted with the SP10. To repeat. It's "drive " is intoxicating. Halcro has used a different descriptor for his TT-101 but he and I agree on the point.

BTW a sine / cosine generator is necessary to create a rotating field in the two phases of your synchronous motor.
In its simplest form it can be approximated by a capacitor.
There have, for decades been more accurate devices available to generate the necessary phase shift, so what you have in the Final,  while being elegant, is not a big deal.

Many DDs have three phase motors. This requires a precision triple sine wave generator. Each wave shifted in phase by 120 degrees. These are then fed into a 3 channel power amplifier.
Since they are direct drive these three phase signals must be very accurate, if they were not the platters rotation would be very erratic.

Most quality DD TT manufacturers did this 4 decades ago.
Again it is not a big deal, but they at least provided the purchaser with the power amp.

Also a synchronous motor like yours has local feedback. The rotor lags slightly the rotating field.
With a varying load this phase angle changes and then corrects, hence incremental speed changes.

There is no free lunch when we try to drive something at a constant speed.