Turntable speed accuracy

Dear Swampwalker, 'Our' Lew is a scientist so no wonder he
use what Wittgenstein called 'scientific grammar'. I would prefer 'indicative statements' above 'declarative' but in any case the 'truth valued ' statments are presupposed. I believe that thinking about different drive systems involves a 'paradigm shift' but not a 'revolutionary' advance in technology. If there were a real revolutionary advances in the technology all TT's designs would use this technology. Otherwise the producers of the 'old technology' TT's would obviously speculate about possible 'sentimental buyers'.

Regards,

Lewm: "The engineers of the 1970s and 80s were well aware of all of these issues that we are now still obsessing over. The L07D may turn out to be my all-time fave, and it's not the highest torque in town."

Good point and good write up. At one point I thought the higher the torque the better and forgot about the increase in cogging. Torque for torque sake does not a good turntable make. I agree that Kenwood knew what they were doing back in the days. Recently I recommended a Kenwood KD-770D, one with a rather low torque coreless motor by DD standard, to an acquaintance and he is so happy that even his wife thinks the sound is smoother and that's with a cheap cartridge. I really think the reduction of cogging by using a good motor is a worthy effort in DD designs. And a precise but "gentle" servo is less harmful to the sound than some brute force detecting system. eg., someone in a DIY forum did the below to his modified Technics SL-Q3:

"I modified the negative feedback loop network to make the whole thing underdamped. As it is from the factory, it is overdamped and after doing some A/B test by switching instantly between the factory network and the new one, it is obvious the change in sound. The modded version is much more relaxed and clear and all the distortion (similar to jitter in digital) in mids and highs is gone."

Some of that sterile DD sound may be caused by the "overdamped" servo, a kind of "analog jitter" Mosin and others mentioned before.

It all comes down to execution, I guess...

_______

Lewm,I struggle with this statement -
"among designers of both belt- and direct-drive turntables there seems to be a divide around weak motor/huge platter vs strong motor/light(er) platter"
I have never associated high mass platters with low torque motors.
If you had said the 2 schools of thought were light platters with sophisticated speed correction or control versus high mass platters with more inertia and less speed correction that would be a more accurate synopsis in my view.

Re the Kenwood L07D and the Technics SP10mk3.
In understanding the design we must remember these turntables were built for quite different purposes or use. The L07D was an all out assault to produce a state of the art tt for home use. The SP10mk3 was designed primarily for broadcast and archival use. Consequently the L07D has one of the most sophisticated plinths of any tt manufactured in terms of rigidity, energy dissipation and ease of adjustability for accurate set up. The SP10mk3 has incredible torque, very fast start up and stop times and a crap plinth.
We dont know what was in the minds of the Technics designers - the choice of the mk3 motor may have been more to do with the fact that it was the motor used in cutting lathes and readily available at the time. What is interesting is that when they increased the torque they also increased the weight of the platter significantly from the SP10mk2.

Well, I couldn't fight the temptation so I purchased a Timeline and received it today. I turn it on, and instead of flashing once every 1.8 seconds, it flashes several times per second (maybe five or six). Does anyone else have this issue? I'm thinking it's defective, but I put it on my table and it seems to flash every 1.8 seconds on several spots per revolution, so it looks as if it's flashing at an exact multiple of once every 1.8 seconds. I check and adjust the speed with my KAB strobe and after a lot of fine adjusting I get the laser to flash consistently on one spot (and the KAB showing exactly 33 1/3 rpm). I lower the needle (I have an album, the KAB, and the timeline on my table) and voila, my table does not slow down with stylus drag. I have not yet done extended time tests yet.

My table is a diy plinth with lenco drive system,a PTP, and a VPI platter. My only complaint is that the speed adjustment is far to sensitive and therefore difficult to set.

I hadn't checked the speed in a while and this experiment seems to indicate it can drift quite easily (likely with small changes in voltage and/or frequency). I see a motor controller in my future.