A Copernican View of the Turntable System

From Nikola's last post I have to admit that having a lawyer with an armpo... sorry I meant to say pedestal :^) -has advantages.

T-Bone - you said.

"The philosophical issue some of us have is that of putting an isolation layer between the motor bearing and the arm bearing."

Why is this ? Can you provide more info on this.

I thought about it. I have limited knowledge of bearings other than actually changing the one in a turntable, as well as the wheel bearings on my trailer and my automobile wheels. I would have assumed that a TT motor bearing is different than an arm bearing both in the way it is designed and works. In fact who here actually uses a table and arm from the same manufacturer even ?

Fleib gave a really good description of how bearings are selected at REGA on the MM thread.

So I am thinking with these two disjointed designs being joined somewhere on a plinth or by appendage - attached somewhere. That this would lend itself to more rumble/chatter, etc...

Remember I have heard an armpod so I have a comparison to make here.

I would tell the design team to separate the two or prove me wrong with test results.

Now lets make it more complicated – a Unipivot arm does not have any bearings but point/s ?

Lets go another level still - an air bearing arm ?

Wonder how those things sound on an armpod ?

At least you are coming up with reasons T Bone. I agree with Henry – with your gear you are the perfect candidate. I am actually selfishly hoping you could provide me with tips to improve my setup based on your experience.

Cheers

Dear T_bone: I understand what " detractors " speaks and asks.

I think that you sooner or latter will be HERE. This excercise is worth to try it even if at the end you don't like what you hear, a learning one.

Regards and enjoy the music,
Raul.

Ct0517,
A pedestal is nothing more than a 'plinth' :^)

The issue of having isolation between the arm bearing and table bearing can be illustrated, in extremis, by imagining a jack-in-the-box with an immovable armpod next to it. After jack has popped out of the box and does not bounce anymore, he is perfectly stable and unmoving at the end of spring. As long as he is perfectly still with absolutely zero resonance, the relationship between your tonearm pivot and jack's nose is always the same, whether Jack is encased in concrete (a plinth) or perched on the end of his spring (on top of a 'platform' which moves in relationship to the world around it. As soon as there is any resonance in the system however, jack will move with regard to the tonearm pivot (and therefore the stylus), and may do so in slightly unpredictable ways. In any case, the slightest movement will cause a kind of intermodulation.

If you fix Jack to the platform your armpod is resting on in order to keep the relationship between his nose and the armpod-mounted arm pivot perfectly constant, you have effectively plinthed him.

If Jack has some kind of internal resonance, the method of fixing him to the board may have more or less resonance. This is the difference between a bad plinth and a good one, but the inherent goal of a plinth is to keep the relationship between the arm's pivot/bearing and the motor bearing as stable as possible. If one removes the plinth which surrounds the motor, and mounts it naked on the same table as the armpod, one has removed an intermediate coupling material (the one which connected the frame of the motor to the bottom of the footers, but one has not changed the concept/goal, one has simply changed the method of execution.

If, however, you stick your TT motor on an isolation base which is not the same base that your arm bearing is resting on, you are effectively changing the distortion relationship. You may find that a substandard plinth will resonate unpleasantly because of a resonant frequency of the material which is in the audible range. If you change this frequency to a 3-5Hz frequency (the goal of most isolation systems), you have exchanged the plinth resonance-induced distortion for one which is like an off-center 45 record.

Oops. Writing on an iphone is a sure-fire way to make lots of typos. So please ignore those.

One can add to the last point that it is not necessarily a BAD thing to exchange one set of undesirable resonances for another set of undesirable resonances. It could be that one likes the flavor of the second better. But for people who are trying to get rid of ALL distortion, introducing an isolation layer (distortion transformer) between two points which are supposed to be absolutely fixed together with zero distortion between them is in some way 'giving up.' And while it may be better than it was 'before', it makes one wonder about the state of the 'before' and almost certainly can be improved upon.

That said, it is not a difficult thing to do, and I will try at some point. I can think that it might even be an improvement on some of my stock plinths (because some of them were not top-notch). I can probably figure out an armpod of some sort relatively easily (it could be an arm attached to an current plinth and the motor outside it, either spiked (rigidly coupled) or isolated (on magnetic levitation footers) with regard to the surface below.

T_bone -
I think you are wasting your time on this. This thread goes round in circles.
If I look at Halcro's system it astonishes me that for all the discussion on turntable set up I see the following issues in his system -
Turntables located on a large resonant shelf behind the speakers where there is massive feedback. There is effectively a bass trap where his turntables sit.
Gear stacked on top of each other rattling away ( yes electrical components resonate when on ).
He has a TV spewing out RF inches away from turntables and sensitive phono stages.
He has a massive glass coffee table bouncing off hi frequencies in front of the listening seat.
I also note that the speakers have huge lips around the edges which will cause a tunneling effect and restrict soundstage.
He may like a horribly discoloured sound who knows, but for me strapping a cartridge on with a rubber band might well sound better in this suboptimal set up.