A new TT from Steve Dobbins,"The Beat." ???

Kftool, Since the platter of your tt is probably bolted to the top of the motor to which the magnet is fastened, in a sense you are free to change the platter, as is true of most dd turntables. The Mk3 is the exception rather than the rule. Most dd turntables are like yours. But the restriction is related to platter mass. The drive system was designed for the mass of the platter, and if you change the platter mass dramatically, then the servo mechanism will not work correctly. Problem is that the permissible range of variation in platter mass for any particular dd setup is unknown to most of us. It's safe to say, I think, that with a massive motor, like the one you have in your DP308, you can probably increase mass by at least 20% without any worries. Probably that is a conservative estimate. The only way to find the upper limit is to do the experiment. As to your other point, I do not know to what degree a heavy platter would work to resist airborne vibrations. Only way to do that is to move the tt to a sonically dead part of your listening room or to outside the listening room, IMO.

PS. You're a lucky guy to have a DP308 and the space in which to place it.

MikeL-based on your comments about the Simply Vinyl Tommy LP, I ordered one this morning. I have a really nice MCA version, but it doesn't have the bottom end you are talking about.

Mepearson, i have 2 different Classic Records 'Tommy's and the MCA, and another 3 or 4 other various pressings. the 'Simply Vinyl' pressing had a much larger soundstage and the bottom is fuller and more impactful than any of the others.

i try to spread out my listening to this Lp so i don't get tired of it; but i seem to come back to it often. why can't they make music like that any more?

MikeL-I too love the Tommy album-it is a timeless classic. I hope I hear that bass punch you referred to in the Overture. I don't think it exists on the other pressings (Track, Decca, and MCA). Do you have a copy of "Won't get fooled again" on MCA? At the end of Going Mobile, there is a really low bass note which sounds pretty impressive.

If you are a fan of the Who, you need to hear Pete Townsend playing acoustic guitar and singing Pinball Wizard live. To my knowledge, it is only available on the Secret Policeman's Ball LP. This live version of Pinball Wizard with just Pete Townsend playing acoustic guitar and singing is crazy good. I am surprised my copy isn't worn to a frazzle but it still sounds great.

Kftool,
The platter of the DN-308, as is, unfortunately rings like a bell. It is the same
design as was on the DP-6000 which was replaced by the double-platter
construction of the DP-80. It is well worth treating I expect (I have not done
mine) and could be worth completely replacing IF you could replicate the
magnetic encoding on the platter which allows for the magnetic pulse speed
check. If the motor is the same AU-169 unit which goes on the DP-100 (and
I cannot be sure but I will give the Denon service guys a call today), then
there is plenty of overhead for a bigger platter though you might have to tune
torque application part of the speed control circuit to "load" it for
a different platter inertia. The DP-100 platter is 6.5kg. Assuming the motor
is the same, the motor would have a built-in suspension (the main spindle is
supported on an "oil cup" cushion above the stator). As for
vibrations, the DP-80 and DP-100 literature suggests that most of the
vibration which is defeated through the double-platter construction is borne
through the frame/spindle/bearing though the DP-80 makes some claim to
its construction lessening 'howling margin' (which is Japanese for
airborne/speaker-induced vibration) which would suggest the DP-100 does
too. In any case, the platter construction benefits of DP-80 vs DP-6000 are
apparent.

One could conceivably build that onto the DN-308 platter through a retrofit
of a spring-leaf system for the platter (If one made it too tall, one would have
to make it ultra tall and cover the spindle too with a new one). I can send
cutaway pics of the DP-80 method and the DP-100 method (which involves
oil-damping wells within the sub-platter to dampen vibrations borne to the
upper platter) if you want.

In any case, I too am curious about what Steve Dobbins has done with the
separation of motor and bearing. As long as tolerances are tight, I would see
no reason why the motor and bearing have to be physically directly-
connected other than that eventually they sit on the same platform. That said,
I don't think I am about to build one DIY...