2020 update : JC Verdier La Platine

@ct0517  yes i saw your pictures and understood construction of your SP-10 plinth system, it is still "naked" or not traditional plinth. Not sure why your SP10 II is not stable, because it is a stable Direct Drive motor and seems like everybody happy with it. 

Personally i have never used a slate plinth, i even started a thread on here about different plinth for SP-10 (from Steve Dobbins, OMA etc), but i gave up and bought another DD that does not require all that mess up with a plinth. The feet on PD-444 are suspended, but the plinth is super heavy metal, no more question about the plinth for me, i am happy. My AT-616 are for Denon DP-80 plinth and for Victor TT-101 plinth. 

lbelchev explained La Platine original concept, sounds good. 
OMA changed the concept using slate plinth for this turntable. 

What i don't understand is your criticism of Direct Drive speed stability. 
Lewis perfectly explained the weakness of the belt drive. 

@lewm
Besides other problems with that, that construction would also tend to be a cause of speed irregularity, as stylus drag waxes and wanes over the course of an LP.

Lewm, here is a nice explanation from the manufacturer Jean Verdier:

"Now, let us approach another point: Dr. G.W. explains that playing a record with a stylus consumes energy and that this energy is variable on account of the changes of musical modulation, resulting in drive speed variations of the platter.

That is absolutely correct and it is one of the basic problems facing the turntable designer. The author than explains how to remedy this: the motor must renew the energy as swiftly as possible to keep constant speed, that is the reason for using a low inertia motor. I think that if this were true, no turntable could work well, because no motor is good enough. Fortunately, we can make use of more powerful tools to settle that problem.

The first tool is well known, it is the platter’s inertia. The heavier platter, the more it works to counter momentary variations in speed, but the challenge is to make a very thick and massive platter which doesn’t ring like a bell.

The second tool is less well-recognized than the first: the constant-coupled brake system. Since the player stylus consumes variable amounts of energy, we have to mask that consumption by permanently consuming much more energy by the use of a brake. The larger the ratio between the energy consumed by the brake and the energy consumed by the stylus, the better turntable work.

To be clear: only a few models of turntables have this device. To understand the concept better, have a look at a Thorens TD 124 which uses a brake with Foucault’s current excited by a permanent magnet, or EMT 927 which has a completely mechanical brake consisting in washers placed around the axle with the capability of adjusting the pressure and therefore the braking action.

On my turntable, the brake is present, but invisible to the casual eye-it is furnished by the axle and bearing. The two parts are unusual in their very large dimensions. The two facing surfaces of about 60 cm2 separated by lubricating viscous oil form the brake."

We can see this brilliant principle in 2020 - CS Port Analog Disk Player LFT1 (£48,000.00): "In LFT 1, the rotation control is not performed, and the constant speed rotation is left to the high moment of inertia of the 27 kg platter, creating a rotation free from unnecessary vibration caused by the control. Only the positive direction force is applied from the motor, but by using a coreless motor with LESS MOMENT OF INERTIA, the influence of the vibration is reduced."

There are more hidden things, but modern audiophiles are looking for exactly 33.33333 ....


Cheers

@lbelchev Regarding the 'braking' action,  Let me rephrase so that I understand correctly. The 'brake' is provided by the viscosity of the oil acting between the axle and the bearing. As there is no vertical force acting on the plinth from the heavy platter due to the replusing magnets, the viscosity of the oil acts as a correcting lateral force to stylus drag. If this is the correct understanding of the 'braking' action then it may explain the drift in playback that I had heard. You see, I had thought the oil as merely a lubricant, so before reading the documents on braking, I had not bothered to replenish the oil reserve. Big mistake!

You mentioned the CS Port LFT1 where the platter floats on air rather than magnets. And it also uses a low inertia motor like the La Platine. The specification given for motor speed accuracy is +- 0.3%. That's between 33.3999 and 33.200, certainly not 33.333333. And that would be the point raised by you and Chris, no need to sweat over 'absolute' speed accuracy. Well taken.

I do have a few questions:

1. The CS Port LFT1 looks like a non-suspension plinth design, with a very heavy slate plinth. The actual resonance control is taken up by the air bearing, whereas the La Platine uses pneumatic footers. If as suggested by @lewm we defeat the pneumatic footers with solid blocks, then there would be no resonance controlling mechanism in the La Platine, as the magnets will not be serving that function. would that be correct?

2. Do you think the use of a low inertia motor only works with a design that decouples the platter from the plinth, either through air or magnets?

3. The CS Port LFT1 is a low flow low pressure design in both its LT arm and platter. Well, the Terminator LT arm on my La Platine is also low flow low pressure. Does that mean I have a poor man's LFT1? He He!

^^^^

1. The CS Port LFT1 looks like a non-suspension plinth design, with a very heavy slate plinth. The actual resonance control is taken up by the air bearing, whereas the La Platine uses pneumatic footers. If as suggested by @lewm we defeat the pneumatic footers with solid blocks, then there would be no resonance controlling mechanism in the La Platine, as the magnets will not be serving that function. would that be correct?

Albert
Your statement is half right as it pertains to the Granito La Platine model. On the Granito model the resonance control is performed by a combination of the plinth and the pneumatic footers.

"Granito is a material composed by little pieces of marble becoming from different origin agglomerated inside a mold with cement.
And of course machined and polished to obtain a good looking result. The resonance of the plinth with its suspension is about 5Hz and it is well absorbed by the air cavities." JC Verdier

"Anyone", that suggests removing the footers and or changing out the Granito plinth - has not come to understand the design, concept, and execution of what is at play.

Furthermore.

The Granito version was very expensive to make. The story is on the Verdier website, and eventually led to the current modern day black glossy plinth. I have an email somewhere from JC Verdier on how a secondary Granito limited run was done at one time for the Japanese market, due to demand.

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Re: Platter System Braking Behavior

Unlike any platter systems that I used to be familiar with, in that they were ....free spinning. This platter system has what I would call, a form of active management.

"The same pole magnets play a part in providing braking action to deal with the records behavior." - JC Verdier.

Albert
With your turntable at speed and no record playing. Turn off the motor. Count the seconds for the platter to come to a complete stop.
Now repeat, and this time just cut the thread. The braking behavior will reveal itself to you.
One comes to realize with this experiment the marriage of the Verdier Motor and Platter System, and how foolish it is to split them up.

Albert, my two cents about La Platine speed stability:

1. Check the axle adjustment. If you use a steel ball check the resistance point between the ball and the spindle. The steel ball should be in contact with the spindle, almost but without pressure. If you do not use a steel ball, the axle should not be in contact with the spindle.  In this case just catch the resistance point and than slightly return back the axle via the adjustment screw. Therefore some play will be necessary (60 to 80th of an inch is sufficient) .The still ball is not absolutely necessary. You can chose to remove it if you want and it is not necessary in such case to modify the adjustment of the axle. If you want to change the mat and/or record clamp it is necessary to adjust the axle.

2. "One of the Verdier’s little foibles: the bottom of the main bearing is designed to leak oil! With an inverted bearing, gravity causes lubricating oil to flow to the bottom of the shaft, leaving the top part dry. Over tune, this oil will eventually make its way to the bottom of the axle where it collects in the axle base cup... If all this conjures up visions of getting out dip-sticks to check oil levels before going for a spin, don’t worry. The oil reservoir is generous, and the rate of seepage low. Also, as the oil is thick, it tends to cling to the sides of the bearing. All the same, this turntable needs rather more maintenance than your average deck..." James M Hughes, "HI-FI NEWS - February 1999"
So, every few weeks 0.5-1.0 cc of oil should be added to the reservoir next to the spindle to keep the axle lubricated. Use the supplied oil or Mobil 15W-30.

Enjoy