Direct Drive vs. Idler Drive vs. Belt drive

This is something I posted in wbf to a gentleman that was against servos in DD TT because he said that he can hear the damage that servos makes to what he listening through a DD turntables ( as the Technics SP10MK3 or Denon DP100 and the like. ) . Could be interesting to think a little about:

""" But things are " critical " for say the least about your " entitled " against servos because the recording LP cutting machines uses DD non-coreless motors as the Technics Sp-02 on the Neumann or the servo controled ( as the Sp-02 ) Parker motor in the Lyrec lathes. In Scully lathes some gentlemans used the MK3 Technics motor. Altivar was other used motor and obviously its own Neumann one and even Denon.

Raul, you miss the obvious.

The Technics SP02 lathe motor was specficially designed to drive the Neumann lathe with the 70lb Neumann flywheel attached.

If you have a low mass platter with direct drive, the speed correction becomes more invasive. With a high mass platter, the inertia and resistance to stylus drag is much higher, and speed correction less invasive.

Furthermore, DC motors have zero torque at constant speed. Torque is only generated when speed change is occurring in a DC motor. Therefore DC driven direct drive turntables are just like digital - only a little bit out all of the time. In your typical lightweight platter/DC DD motor, it is most likely the platter is seldom at the correct speed at a micro level.

Furthermore speed correction with a DC motor can be scoped - it is a saw tooth trapezoidal recovery ( rough in plain language )  compared to an AC motor recovery which is sinusoidal when scoped ( much smoother and more consonant with music ).

By the way, most of the vintage lathes are worm drive.

Dear @Dover : Agree but that does not means dissapears, only " less invasive ". problem is that we can’t know what that means exactly.

In the other side gentlemans ( other than ML. ) that own the Technics MK3 did not posted about " problem " with the servo. I owned the MK2 and never detect it against BD TT neither with my Denon’s and if I rememeber Halcro neither in that specific issue or even lew.

What I said is that what we can detect in a DD vs BD/ID TTs couldbe a " trouble " with other kind of DD designs characteristics and not because the servo.

R.

By the way, most of the vintage lathes are worm drive.

Furthermore, DC motors have zero torque at constant speed.

@dover  These two statements are false. I own a Scully lathe which is typical of what was used to make many older recordings. Its not worm drive. It employs a 1/8th horsepower syncronous motor which drives an anti-vibration coupling which then drives a transmission (which allows for shifting from 33 to 45 rpm). The transmission employs bevel gears in an oil bath but no worm drive. Its output is a shaft which drives another vibration isolation coupling; that in turn drives the platter directly, which rests on a set of carefully machined bearings (which require frequent attention).


DC motors have torque even at constant speed, so long as there is a load. This link might be helpful:

https://www.motioncontroltips.com/torque-equation/
However its a bit of a misnomer to equate a servo controlled multi-pole motor with a simple DC motor, and its also worthy of note that AC motors have a similar property of lockup being the point of highest torque output (as I'm sure you know quite well). I'm guessing that what might have been conflated/misconstrued in your comment above is the fact that when a motor has no load, its **current draw** is its lowest. But I think you'll find that how much torque it has is another matter altogether! Certainly a motor at constant speed will be making torque...
Its one thing to 'scope the waveform that is driving the servo operation, its quite another to see how the system responds to that waveform. I very much doubt that the platter speed variation can be represented by a triangle wave!

Atma-Sphere, I have noticed on several recent re releases and aggravating degree of rumble transferred to the record. I have always assumed this was from poor maintenance of an older lathe. Your last post would confirm this. Does anyone still make lathes? Can you get parts for older lathes and keep them running at spec? Is a high quality modern turntable quieter than a lathe?

I think everyone should take a deep breath and put on a record. Between tracks turn up the volume and listen to the noise. What happens to the noise when the music starts. How quiet does the music have to get before you can hear the noise again? I think we can all agree that that background noise is a form of random distortion, probably in the order of 3 to 100% depending on the volume of the music. But, when the music gets loud enough it disappears. Try as hard as you can you can not hear it (unless there is a huge scratch) If you can hear it, it is time to throw that record away and get a new copy. 

My point in all this is that this noise is several orders of magnitude worse than any aberrations cause by even the least expensive audiophile turntables available today. These discussions are fun and alot of these arguments have merit and may influence your purchasing decisions.
The best turntable is always the one you just bought. Why else would you have bought it? In the end speed stability and wow and flutter are trivial issues next to rumble and isolation. How often has someone complained on this web site about wow and flutter? How often does someone complain about their woofers "pumping?" How often do people c/o foot fall skipping?

AC motors are king because they auto correct on the run. They will add or subtract torque to maintain whatever frequency they are being fed. As long as that frequency is perfectly stable you are in business. 
Correction of DC motors always occurs after the fact and is a more complicated endeavor. Can you hear a difference? You can't even hear all that crap underlying the music on your records. 
  

Can you get parts for older lathes and keep them running at spec? Is a high quality modern turntable quieter than a lathe?

With my lathe its helpful knowing a machinist :)  No worries keeping it at spec. I think the Technics SP10 Mk3 is in the same ballpark of speed stability; most turntables are not. But the Technics motor was meant for LP mastering anyway.


With regards to surface noise I agree most of that is in the groove, not the turntable. The faults of turntables seem to be speed stability (heard as a shimmer in the soundstage; if you get to play reel to reel you'll understand what I mean right away) and resonance in the plinth, tonearm tube and platter. With regards to the platter, it has to be dead, and also control resonance in the LP itself- which is not a trivial matter! While the former seems to be understood in high end machines, the latter seems to get little notice, even though its just as important.


The surface noise is mostly an artifact of the pressing plant, although I do notice when the mastering engineer speeds up the cutter threads to cut the leadout grooves at the end of the LP. Otherwise though I simply don't get rumble despite the electronics having full bandwidth to 2 Hz.