Tonearm mount to the plinth vs arm board vs rotating arm board vs isolated tower

Actually, a huge "THANK YOU" to all three of the above, who guided me to the above design. Also to the late Tom Fletcher. I certainly could not have done it without you.

I agree with @halcro , it is essential to isolate the tonearm from the platter bearing and the motor.

I also agree with @atmasphere , it is essential to have the tonearm rigidly connected to the platter bearing.

I also agree with @lewm , bolt the tonearm to the plinth if possible, but compromise as necessary.

There is a material which is highly rigid, on the same order as aluminum plate, which is also very highly damped. That material is panzerholz. I built my platter board out of panzerholz and glued a layer of carbon composite to the top for further rigidity and constrained layer damping. Then I bolted my tonearm to the platter board.

Bearing is all air - high pressure amorphous carbon bearings in three dimensions. Bearing is grounded by offset steel columns connected through panzerholz blocks from (slate) tabletop to platter board. Platter bearing noise is nil.

Outboard belt drive with a flywheel allows excellent isolation of the motor. I say, "Let's have it all !"

@fsonicsmith , sorry to offend you. I was merely attempting to contribute to the discussion by suggesting that these desired characteristics could be obtained without (much) compromise, in part by finessing the problem, and partly by choice of materials. On re-reading my post, I realize that I was imprecise. I could cure this, but it might be tedious. Incidentally, baltic birch is a poor substitute for panzerholz. Ask me how I know.

@atmasphere , my imprecision obviously bothered you as well. I was trying to express the idea that an air bearing could be made silent, and so finesse the problem of transmitting platter bearing noise to the tonearm. I agree about a rigid coupling, which is incorporated into the design.

@fsonicsmith , No. I did not say that my TT was perfect. Goodbye, Mr. Smith.