Support table or shelf for turntable

The springs route isn’t all that complex, I’m more than happy to help where I can..

Placing my turnable on a spring suspended butcher block platform reduced significantly any sounds caused by hitting my rack. I really have to hit it hard to get any sound to transfer to the speakers.
If the coupling/shelf route doesn’t quite work 100%, you should definitely consider springs.
That being said, rollerblocks seem like they'd add isolation in the horizontal plane as well as isolation from torsion, which certainly wouldn't hurt.

Noromance, I hope I am not pointing out the obvious here, but the slate, by itself, won't isolate your 401/plinth from your existing table (if I'm understanding this right, not knowing if the slate will be on the top of the plinth, or under it). Isolation from the table is the key to success.

If you would, please report the outcome, for we of curious minds.

Regards,
Dan

@islandmandan Yes, I know that the slate will not isolate the table. I want to try the slate plinth as I believe that the birch-ply, while excellent at damping TT generated noise, is also responsible for a little smearing and subsequent loss of some detail. The relatively difficult, and frankly, cumbersome efforts to isolate the table can be ameliorated by wall mounting to concrete and keeping the structural hardware to a minimum.

Actually, slate or marble or granite, assuming it’s not too thin, provides significant isolation against rotational forces attempting to bend the plate or slab, by virtue of its mass and stiffness. I am a big fan of bluestone, the gray blue stone usually used for paving, for its low cost and high mass and stiffness. Thus, the effectiveness of these heavy thick stone slabs with springs.

I'm just happy to see Michael Green's (Room Tune "guru") proposal of component "tuning" by constraining outer structures with spikes falling out of fashion. Wrongheaded then, wrongheaded now, wrongheaded forever! We want decoupling (isolation), not coupling, right?