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Constrained Layer Damping and the VPI Classic 3 (long)

One of my current fascinations is with old belt-drive Empire 208 turntables, said to be one of the inspirations for the design of the new VPI Classic series of turntables. Some of the main things the Empire has going for it are a very good Papst eddy current motor, a nice, close-tolerance sintered bronze oil main bearing, and a lovely high-mass cast aluminum platter. Notably, the motor is mounted within the plinth, and the coupling between the tonearm geometry and the center spindle is quite rigid. I can see where VPI is using some of these ideas in the Classic 3.

When I get an occasional weekend to tinker around in my shop, I've been rebuilding an Empire 208 that I bought last Christmas. Fortunately, these are well-trodden paths, and a number of audiophools have posted their musings, their pictures and their results in modifying/upgrading these classic Empire tables from the early 1960's. I've been learning a lot from these folks as I progress in my rebuild. Currently, I'm machining a new base plate for the turntable.

I've read several scholarly papers on Constrained Layer Damping, yet I am not an engineer, so I'd like to borrow successful ideas from anyone who is willing to share. I've been to the AudioQualia sites to look at discussions of different plinth materials (and found a fair amount of mis-information there as well). They're all hot on things like Panzerholz (used by Clearaudio) or Epoxy-enrobed kitty litter, or plaster of paris... Whew!

My new base plate is 1" thick aluminum stress-relieved plate. If I suspend it from a string and strike it with a hammer, it makes a lovely tone (rinnnnnnnng). This is not necessarily a good thing for a turntable!

I see that Harry Weisfield has a thick 1/2" aluminum plate in the newest Classic 3 turntable, and apparently he also uses a sheet of 11 guage? steel and 2" of MDF in a CLD sandwich to dampen the platter and add mass. Very cool!! I think I'm in love!

I know that (as with all things audio), everything matters. Thus, the ratio of the thickness of the materials used in a CLD sandwich is important, as is the presence or absence of glue/silicone or other bonding agents in between layers. Or even the application of specific layers such as EAR Isodamp. There's a white paper on the EAR website about using Isodamp in the construction of a high-end turntable in conjunction with a couple of layers of slate. But I'm struggling to put together the best configuration for my build.

So, does anyone know the actual construction details of the Classic 3 base plate? I know that it is a substantial upgrade relative to the Classic 2. I'm already committed to the 1" thick dimension of the base plate. So I'm now trying to figure out what might be the best combination of other materials and their optimal CLD configuration relative to the 1" aluminum base plate. Of course I'd also like to minimize the number of alternatives I'll need to build and listen to in the process.

Can someone point me in the right direction on this?



"Knowing what you don't know is, in a sense, omniscience"


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Topic - Constrained Layer Damping and the VPI Classic 3 (long) - CometCKO 15:45:54 07/23/12 (11)

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