Vintage DD turntables. Are we living dangerously?

Richardkrebs, I agree with you on many points especially about torque. And I'm glad that you are able to enjoy a modified version of the Technics. I just wanted to add that the higher torque the higher cogging and it's a challenge to increase one without increasing the other. Your unit seems to overcome the sound that includes "a tension, stress if you will, to the presentation and a greyness that over time is downright irritating." Well said! I guess coreless motor offers a good compromise for me. Does that make me belong in the "low responsiveness camp"? Can I bring some Clash records for a spin? :)

I'm sorry that I sounded rather negative on the Technics line. I actually have fond memory of the SP10mk2 and, who knows, might even revisit it one day.


Happy listening!

Hiho
Thank you for your considered response.

Re the contentious subject of cogging.
Coreless motors cog, as accidentally powering up a Goldmund Studio without its platter, clearly demonstrated. ( JVC 4 pole, 2 phase, coreless motor). It was a dumb thing to do, but informative never the less.

The problem that you rightly ascribe to the SP range is not IMO cogging.
It is way too high in frequency to be so. The motors have 15 stator poles, don't know how many mag poles, but some higher number.
Making around the mid 200 HZ of power pulses per revolution. But they are 3 phase motors, each phase separated by 120 degrees. The sinusoid supplied phases slide into each other, improving linearity considerably, so "power pulse" would seem to be the wrong term to use.
The SP10s higher pole and phase count than a number of coreless DD motors, would imply, for a given output torque, lower amplitude but higher frequency cogging.
( The motor only delivers the torque asked of it under the load conditions at that moment in time). If it delivered higher torque than the load demand, the platter would accelerate.
I hear the problem in a standard SP10 in the kHz range. This is a feedback speed sense issue and is not intrinsic in the motors architecture and any cogging that it may produce.
It can be fixed.

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.