Vintage DD turntables. Are we living dangerously?

Thanks for elaborating, Richard. I am learning a lot about motor. Would you say the irritating "greyness" from the Technics is due to this high frequency "pulse" created by the feedback network? Can the remedy be applied to other brands of turntables?

Quite honestly, I don't really care what kind of motor is used in a turntable as long as it does not contribute that negative sound quality you mentioned. That jittery sound once heard is easily recognized but hard to ignore and I've been avoiding it ever since I switched to other smoother sounding tables. I'm glad there are technical people like you out there addressing the issue. It's about time to shut up the DD naysayers! :)

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Hiho
I think that the greyness is produced, amongst other things, by errors in the speed sensing mechanism. These are due to the way they are put together which can be corrected. I don't think that "pulse" is the correct term for this phenomenon.
IMO the technics TTs get into trouble because they have so much correction torque available. They can respond faster than most TTs to error signals. Even if these error signals themselves are erroneous.
My treatment method is applicable to any DD TT.

The term " jittery" you use is spot on and is what I use to describe the effect on my krebsupgrade web site.
Once heard it cannot be unheard!

Previously when the 'STOP' button was pressed...the platter instantly stopped due to the reverse current in the drive circuit....and then reverse spun for a second before stopping. This reverse spin was due to my removal of the stock heavy rubber platter mat which I have substituted with the lightweight Victor pigskin.

As you might already know, Halcro, the force of the reverse current can be calibrated via adjustment of variable resistors in the circuitry. My tech told me that the adjustment would be a PITA to do because he would need to build something to lift the turntable up a couple feet so he can put his test probes underneath while the table is running. I guess if one wants a perfect table, it might be worth doing. But of course the calibration is tied to a specific weight mat; change the mat and one would need to recalibrate. I left well alone.

In this discussion of those horrible SP10 Mk2 and Mk3 turntables, let me point out, as I did to Richard privately, that there is a world of difference between Mk2 and Mk3. I think I can say that with some authority, as I have owned both, in similar plinths, serving as signal source for the same system in my home. The Mk3 is worlds better in the area of grayness or "irritation" compared to the Mk2. I could and can happily live with my un-modified Mk3, and I do not hear the problems I associated with the Mk2. With the Mk3, one has a very energetic sound that could be accused of erring on the "clinical" side, whereas I definitely did hear the gray-ish coloration with the Mk2. That said, I am a believer in the Krebs mods; I've just got to get the cash together. Every Mk3 owner who has had the Krebs work done is ecstatic, so far as I can determine. (Do you think I should sell a turntable, maybe?)

Richard, Did you refer to the Technics motors as AC synchronous types? Since the PS puts out pure DC, I assumed they were DC motors.

Lew.

Yes the SP10s are DC motors. Maybe the confusion arose when I said that they are 3 phase. The supply voltage does not swing across zero.

cheers.