Direct Drive vs. Idler Drive vs. Belt drive

An update to my last post. A point I didn't make clear. 
The change in angle between the  rotating field and the rotor due to dynamic changes in load is a momentary change in platter speed. It is measurable and audible. Over time the average speed does not change, so we would not see this effect with say the Timeline laser. This, because it only tells us if the average speed is correct. These multiple subtle speed changes go unnoticed when this type of  measurement is used. We need to use much higher levels of granularity to see them. 
Further we do not perceive them as actual speed changes. ("that piano decay is wavering") isn't a descriptor one would use for this effect. It is more along the lines of solidity. Can we imagine walking up to the sound and actually holding it. Does it have mass and texture. These features are negatively impacted by these micro speed deviations. 
An aside, the cartridge doesn't differentiate between a change in platter speed or a momentary change in platter/ arm position. Both actions will be interpreted as a speed changes. So we need to have brilliant bearings in the arm, we need to pay close attention to the paltter bearing, the mounting of the arm with respect to the platter and of course we need to carefully control any tendency for things to resonate. I think that the key imporvements we will see in future TT designs will be the holstic attention to this time domain parameter. 

cheers.    

 

why servo’s suck.....

In order to pick up sound accurately from the analog disc, the rotation of the platter must be rotated at a constant speed without any “fluctuation”. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. Although this level and cycle are determined by the gain of the control system and the loop speed, the period of the speed control of the platter which is the mechanical system surely comes into the audio band. In general, accurate rotation is obtained by servo control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. If you try to measure a period with a small level, you can not measure the instantaneous state, so you measure the average value. Therefore, fine vibration generated by servo control can not be measured by the measuring instrument, it depends on the human ear.

yes.......the human ear.

when we consider belts, idlers, and direct drive........2 of those have the choice of no servo’s.

i’ve owned a number of top flight direct drive turntables; including the Rockport Sirius III, the SP-10 Mk2 and Mk3, and now the Wave Kinetics NVS for the last 9 years. taken singularly; none of those were obviously lacking in speed solidity and musical flow. but over these last 6-9 months, in direct side by side comparison to the Saskia model two idler, and the CS Port LFT1 Belt drive, neither of which have servo’s......this idea of the human ear hearing the musical cost of feedback is very real.

execution of an idler or belt to the degree to take full advantage of the lack of feedback is paramount, but when you do your ’ears’ will thank you.

I agree than servo feedback can cause some compression.
But if the motor-platter system has a smaller inertia the harm is leser.
Because that EMT 950 that has a very powerful motor and very light platter sound best and most dynamic compared to other DD turntables.

Yes, the belt drive have advantage of very low noise.
BUT, when you listen an orchestra,on one hand you can listen a 10th violin separately and other small details, but on the other hand the rhythm and flow of music is broken by belt drive momentary speed fluctuations. I think the rhythm accuracy and flow of music is much more important than small details.

I agree than  servo feedback can cause some compresion.
But if the motor-platter system has a smaller interia the harm is leser.
Because that EMT 950 that has a very powerful motor and very light platter sound best and most dynamic compared to other DD turntables.
Belt drive have advantage of very low noise. But OK, when you listen an orchestra,
on one hand you can listen a 10th violin and other small details, but on the other hand the rhythm and flow of music is broken by belt drive momentary speed  fluctuations. 
I think the rhythm accuracy and flow of music is much more important than small details.

atmasphere's (Ralph's) point about tension on the spindle with the belt pulling to one side was addressed by one table I'm aware of.  I owned an original Well Tempered TurnTable and the spindle well had five contact bearing points.  Two were inside the well (maybe 45 degrees apart?) near the top nearest the belt position, two more were nearer the bottom of the well and opposite position of the upper two, the fifth was at the bottom of the well in the normal position.  This way the tension applied by the belt held the spinal shaft against the upper two bearings while a vertical position was maintained by the two opposite bearings lower in the well.  The spindle shaft could wobble within the well until the belt was installed to bring it vertical with pressure on all five bearings.  I don't know if any other manufacturer adopted this simple but ingenious solution to retaining a vertical spindle shaft? 

i’ve owned a number of top flight direct drive turntables; including the Rockport Sirius III, the SP-10 Mk2 and Mk3, and now the Wave Kinetics NVS for the last 9 years. taken singularly; none of those were obviously lacking in speed solidity and musical flow. but over these last 6-9 months, in direct side by side comparison to the Saskia model two idler, and the CS Port LFT1 Belt drive, neither of which have servo’s......this idea of the human ear hearing the musical cost of feedback is very real.

execution of an idler or belt to the degree to take full advantage of the lack of feedback is paramount, but when you do your ’ears’ will thank you.

At 53K before tonearm I would hope the Saskia has what your previous DD’s did not. I would love to hear one to compare with my much less expensive set-ups. I have maybe 18K in my hot-rodded 301. 4K for a nearly NOS drive unit. Close to 2K for a solid brass platter, another 1K for a solid brass spindle/main bearing, close to 2K for a PSU to decrease motor noise, 3K for a custom plinth that weighs 50 lbs or so in layered cherry with cocobolo outer veneer, another 2K for things like an AS idler wheel and stillpointes, and 4K for my Reed 3P arm.
I trust yours sounds even better (since you are a regular on what’s best) and I happily surrender as to bragging rights and perhaps curb appeal. I can not convey how much pleasure my 301 gives me in every way. I have grown to love it more than my totally hot-rodded TD124 with nearly identical improvements and arm. By a smidge.
Both combine the durability of transcription table design with modern aspects and yet again with vintage aesthetics.
To me and perhaps me only, a turntable need not look like a piece of laboratory equipment. And I don’t think the Saskia looks like lab equipment, but stuff from TechDas et al.......