Tbone et al, In the DP80, when you use the adjustable speed control you are bypassing the quartz crystal oscillator. That's the only way you can get the electronics to agree to change the platter speed, I guess. If the electronics are all copacetic, the platter will turn at exactly 33.33 with the quartz oscillator engaged, but the speed is not adjustable in this mode. This mode is much like the SP10 MkII. Presumably, it's preferable in terms of speed stability to have the quartz oscillator in play.
Raul, Upwards in this thread we discussed the Denon plinths a bit. Kcc123 has a DK2300 plinth, which is a two-arm job and looks like it has nice high mass. Today I hefted my DK300 plinth. It's a laminate of possibly some good quality plywood or hardwood and very heavy; I imagine the DK2300 is even heavier, because it is bigger in order to accomodate two arms. So I am thinking that these plinths might not be so bad. What needs to be improved is the coupling between the tt chassis and the plinth, and I intend to try to achieve that by using much thicker and longer wood screws. Or long bolts that go clear thru the plinth to the bottom side. This small mod plus the dampening of the hollow ring around the platter (see my post above) may be quite effective upgrades, without resorting to a home-made plinth. I do have a piece of slate for the DP80, if that strategy fails.