A Copernican View of the Turntable System

Nick_sr,
The approach you describe is a common one and has been in use by different manufacturers for decades.
This thread is simply proposing a differing approach albeit one which still maintains the geometrical relationship between tonearm and turntable.
No-one here believes movement in that relationship, should be tolerated?

Halcro, I am not opposed to your approach, in fact I find it attractive. Your idea of the concrete arm-pod seems like a fun DYI project that I have considered for use on SL-1200 table. But that got me to analysing this approach and the big hurdle I see is locating the arm-pod.

Really my question is how can you guarantee this geometric relationship when considering using a Baerwald type set-up. With this type of setup we are taking about degrees of precision in fractions of milimeters. I have trouble seeing how simply placing, with out any means of mechanical fine adjustment, an arm-pod on flat surface(albeit very diligently and carefully)can provide such a degree of precision. Can you explain the approach you use?

One Idea I came up with would be to have mounting locations machined into the base used. But in doing so you then be coupling the arm-pod and turn-table to the mounting surface, and you would essentially be back at square one.

Hi Nick_sr,
The Copernican view of the armpod and tonearm as the centre of the turntable system, is predicated on the fact that the armpod is an 'immovable' object.
How that is achieved is open to debate.
I prefer to see mass (and plenty of it) concentrated on 3 spikes which would be equivalent to tons per sq in 'digging' into the supporting shelf.
You would be surprised how difficult this is to move without lifting the pod off one or more spikes. And that is how the correct Spindle to Pivot distance is accomplished......by tiny lifts and nudges of the armpod.
Until you try it you won't believe how easy it is and how accurately it can be achieved.
As you correctly say........isolating the tonearm from any motor noise or platter vibration is a huge benefit and can only be achieved in this way for Direct Drive and Idler design TT. Belt-drives can have (and often do) their motors isolated from the platter and plinth via a separate module.
The degree of stability and ease of set-up is something that differs with each solution and is something you quite rightly point out.

Nick_sr,

Btw, I don't think what I have tried to say necessarily disagrees with your points, particularly about residue vibrations and the like. As I said, I have simply sought to understand what I am hearing in a (possibly) completely 'unscientific' way. Uncertainty therefore remains about the why's. What is not in doubt is the what's: i.e, very, very high quality and believable play back.

Nick sr,

I imagined that the turntable produces vibrations when it rotates. These mechanical rotations are not the same as the indentations on the record and would be transmitted to a coupled tonearm (no matter how small the transmission). To isolate the tt is to isolate it from external vibrations but not its own self produced ones: here you can consider the difference that we get from isolating CDp's say with rollerblocks or the like!

To decouple the tonearm from the tt would therefore be to remove these additional vibrations. The issue about mating with the vibrations on the record would then (once the decoupled tonearm and armpod are equally isolated) become a question of the quality of bearings and trackng force accuracy and of the ability of that tonearm to match the movement of the indentations that are on the record's surface.

This is just me trying to understand what I hear in a (possibly) completely 'unscientific' way.