Vintage DD turntables. Are we living dangerously?

lewm
03-15-2016 12:10pm

JP, can you amplify on your cryptic comment about the effect of a heavy platter mat? "Drive gain"?

Okay, but I’m more than rusty on root locus and complex conjugates. :)

My very hasty research this morning indicates rotational mass isn’t going to have an affect on the PLL if the drive is compensated. It may not have a meaningful effect regardless.

Increasing the rotational mass means a given correction to be performed in the same amount of time will require more energy. If not the reaction time will be slow. Note the sync position timing for the MK2A and MK3 are the same, yet the MK3 platter is just over 3x heavier. Most of that mass is inboard but it’s still a significant difference.

I think this is one of the reasons these DDs can be so polarizing - there’s no way to tell how different techs are calibrating them without measuring one first-hand, thusly no way to really know that they’re performing the same. A MK3 can be dialed back so far the motor will actually overshoot and bounce off phase lock 2-3 times before settling, or set over-critically such that the drive MOSFETs will self-destruct in seconds. I’ve mentioned I’ve seen these running in belt-drive emulation mode before - that’s wasn't a joke.

I haven’t measured a MK3 or MK2A with additional platter mass. On the MKII the W&F measurements were negligible, but I don’t think that’s a spectacular measurement for how a drive system reacts to real-world conditions anyway; more of a steady-state baseline.

The TT-101 at a block level is really no different than an SP-10 aside from what it takes to drive their coreless motor, so I wouldn’t expect a little extra mass is going to have a broad affect on what you hear. The motor will not be as critically controlled, though depending on the mass that may be negligible, or actually preferable.

dd
The Denon DP-80 has the saucer shape like the Victor TT-101. In fact the Victors copied the Denon look. I have a copy of the DP-80 mounting template.

Was it the chicken or the egg with regards to the copying.
But we won't get into just who did the manufacturing and design not that it matters.

JP, Thanks very much for your informative response. If you ever do get to do some additional experiments with DD’s toting heavier-than-OEM platters, let us know. 

Here is a question that maybe Totem or Peter can answer, particularly Peter: Will a TT101 fit into a plinth made for a DP80? Here I am asking only about the hole in the top deck and the placement of the bolt holes. My DP80 is sitting in a very nice slate plinth cut for it. I might like to try the TT101 in that same plinth, but not if it requires modifying the slate. Obviously, I could just try it, but that requires me to do work.  Hate that. Thanks.

Lewm, 

Unfortunately the metal casing that house the electronics on the TT101 is larger in diameter then on the DP80 (DP80 =10.5" Diameter) (TT101=11" Diameter).

I'll be making a very nice plinth for my TT101  maybe you want one too :-)


Good Listening


Peter

Yes, I measured the circumference of both, and I noticed that the TT101 casing/shield has a larger circumference by about ~1.5", which, divided by pi, would be consistent with an ~0.5" difference in diameter.  I had hopes that the Denon cut-out would accommodate this slight difference, but I can see why it would not; the bolt holes run pretty close to the circumference. (I supplied the water-jet guy who cut the plinth for my DP80 with a template I made according to a factory drawing. He did a superb job.)

I do have the QL10 plinth for my TT101.  I replaced the MDF tonearm mount board with one made from aluminum.  I then also re-enforced the remainder of the plinth with slabs of aluminum bolted to the bottom, wherever there was room.  One large piece of alu runs across under the tonearm mount opening, and a large bolt conjoins the piece under the chassis with the new aluminum mount board,which is drilled and threaded to receive the bolt.  Thus I've increased mass, ridigity, and created a little constrained layer dampening, between MDF and aluminum.  We'll see how that sounds.  In my opinion, the plinth is where Victor really dropped the ball by comparison with Technics, Pioneer Exclusive, and Kenwood.  It's nothing much by itself. Same goes for Denon with the DP80, which is why I am sure your DP8(?) is a huge upgrade over the stock DP80 plinth

I have a longtime friend who is a professional machinist, owns a large business making scientific equipment.  At his home, he has a machine shop that is beyond belief, analogous to what we would do with unlimited resources to put together a vintage audio system.  He has huge lathes that are no longer made and every possible accessory for them.  And he loves to mess around.  If I ask to use his equipment to drill or cut, he ends up taking the job over from me, and does the work far better than I could ever hope to do.  So, it was really he who made all the aluminum parts for the QL10 plinth. Then we get stoned.