Tables That Feature Bearing Friction


I recently had the opportunity to audition the DPS turntable which, unlike most tables, has a certain amount of friction designed into the bearing. This, when paired with a high quality/high torque motor, is said to allow for greater speed stability--sort of like shifting to a lower gear when driving down a steep hill and allowing the engine to provide some breaking effect and thus greater vehicular stability. I am intrigued by this idea and was wondering what other people thought about this design approach. Are there other tables which use this bearing principal? One concern I have is that by introducing friction you may also be introducing noise. Comments?
dodgealum
Dear Mrjstark, dear Teres, if there is more then theory, then we are either in mysticque or religious grounds.
Different belts having different (negative and positive) effects on the bearing an dteh rotating mass system and on the transmission of vibrations is certainly no mystery nor unexplained by sience.
Dear Lewm, a no force belt/thread/string driven bearing is done this way: picture the motor left of the platter. On the right side - same distance as the motor to the bearing - is a 2nd spindle (or easier: motor without active force) which mirrors the position of the drive motor. Here the belt/thread/string finds a 2nd pulley equal to the one on the motor. The spindle of this "counter device" should be same as teh motor sindle and all its moving parts shall be equal dimension and material.
Correctly done, there is now no resulting force anymore on the bearing in horizontal / lateral plane/dimension. The force of driving has 2 equal vectors now which do give which do zero each other regarding their effect on the bearing as they do go in opposite directions.
Dear Kirkus, the "controlled slippage" is tricky to set-up, but if used with the "right" (= close to zero elasticity) thread it is very durable and does not request to be re-adjusted.

The drive-system is - as always - a matter of quality in the selected parts. I still do favour using any of the big Studer 800 capstan motors as drive motor for a "good" turntable. These capstans are expensive -yes. They require some pretty expensive periphery too - yes. But they are a totally different league.
These capstans are at work since the 1960ies in almost all great recording studios and a majority of all music recorded between the late 1960ies and early 1980ies (and beyond...) were recorded with these capstans being a direct and very paramount part of the big tape recorders.
Use one of these and give it the regulator circuit is needs and 98% of all problems with other motors and drives are vanished. Motor-born vibrations are minimized too.
And yes - it will cost you about $2000 alone in parts.
Quality NEVER comes cheap.

As for the clamping platter record interface. I do have the solution for that problem at hand. It however is rather expensive and labour intensive again. I do not think it makes sense to unfold it here.
The discussion about again too expensive and not suitable for a commercial product and crompromise etc. will just go on and on.
In general we shoul decide, whether the main subject is how to design a turntable as a commercial product, or how to design a turntable which tries to reach the limits of playback possibilities.

I must admit that it is rather depressing for me to read in these posts so frequently that "this gets too expensive"....."have to made trade-offs".........."well-choosen compromise"........ "bring to market"........"commercial product".

This all sounds like the usual political paraphrases.

As was mentioned before - if we do not demand and strive for the best possible (an audio industry will tell us it is the "best possible" anyway every 4-6 months...) - we will only get what we have got so far:

......mediocrity.........
Time to add something to the physics discussion here:

if there is more then theory, then we are either in mysticque or religious grounds.

I would like to clarify this a little more since there is a lot of confusion on words, especially on the terms physics and theory. There are several reasons that a theoretical prediction doesn't agree with praxis (and none of the reason invalidates the theory or physics in general). Without going into too much technical detail:

- First of all physics does capture everything in the world and the physical laws certainly apply completely to turntable design or to the electrical processing of the signal for that matter.

- The real problem is, we are dealing with complex systems: Yes, Newton'sche Mechanic describes the basic mechanical motional aspects of a turntable completely. And things like vibration transfer in the platter, tonearm, etc. are covered by solid-state physics. However, most of the equations one ends up with when describing a system completely is far to complex to be simulated on a computer.

- For example, we could describe every microscopic particle and its motion in the turntable; the problem is there are more than 10^25 particles in a turntable; i.e. 10^25 coupled nonlinear equations. With our standard computers we would have to wait a few thousand years for the computation to finish.

- Thus certain approximations and assumptions are generally applied which simplify the equations and make it possible to calculate the system behavior. Most of the times this gives a good enough "picture" of the system behavior, but quite often calculations and predictions do not capture every detail and minor aspect ton include these details we would have to revisit our assumption, include less approximations and more terms in our description which in turn makes things complicated to calculate and predict again.

- As a result, practical trial and error is often a lot easier which is why some (like Teres and Mjstark) would probably refer to turntable design as “art rather than science”. Now, basic simplified engineering equations may not describe the results of our excellent practical outcomes, but the underlying physics is still accurate, but just too complex for a full calculation and prediction.

- A lot of the things we are talking about here (belt creep or slippage, effect of different belts, different pulleys, stylus drag, etc.) are higher order corrections that are difficult to model, but easy to try out in praxis. Even the Apollo missions rely on practical trial and error in the development stage as well as practical tests in addition to basic physical principles.

- Finally, some semantics: There is a subtle distinction between the terms "Theory" and "Hypothesis".The terms are often used interchangeably which is incorrect. Scientifically there is a big difference (see for example the Wiki)

- Just because a system is complex and difficult to predict it does not necessitate religion or mysticism. Similarly, just because we don't measure an effect, but we hear a difference doesn't mean the physics is wrong; it just means our approximations and theoretical assumptions are wrong and/or we measured the wrong things.

Bottomline, we could probably achieve a lot more with a careful scientific description of turntable design (as Dertonarm instigates), the whole audio system, and even human hearing. But in praxis, trial and error and careful listening is still a lot easier and effective in achieving better results (which strengthens Teres’ point).

This is just the perspective of a physicist of course ;)

Rene