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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"
Follow Ups:
Make the steel weigh as much as or close to the aluminum as you can and thw wood half the weight of the aluminum and you ae there.
HW
VERY cool! Thank you, thank you, thank you!
Next challenge is figuring out best way to bond them together. Not keen on running bolts, maybe one of the flexible epoxies? Silicone glue?
Your contributions to the enthusiast community are fantastic; one reason why I'm proud to own some of your machines. The 16.5 RCM revolutionized vinyl for me and I still play my Scout a couple hours every day... Love it!
"Knowing what you don't know is, in a sense, omniscience"
Adhesives are a one way trip. Trying to undo a bad adhesive decision is really tough.
Especially if you want to save everything.
As a machinist I prefer fasteners. And if your choices are so check mated by permanence.
I was really pleased with the performance of the 3M DP-105 adhesive when used as a damping agent in the Empire platter. But if I did not like the result, it was an essentially irreversible decision.
I also think that different adhesive materials are quite variable in their sonic impact when serving as a middle layer in a plinth sandwich. It sounds expensive to do a lot of trial and error.
Anyway, I plan to listen to the HW-recommended combination with clamps before I make any irreversible choices. Thanks for pointing that out!!
"Knowing what you don't know is, in a sense, omniscience"
Clamps might have a sound too. Aluminum vs forged steel....
Actually it sounds like an interesting experiment. As well as examining the effect of clamping pressure, distribution of force, etc.
If I were using bolts, I think I'd play with golden mean proportions to place the clamping forces on the plinth.
Any suggestions based on your experience?
Thanks again!
"Knowing what you don't know is, in a sense, omniscience"
I have built a few empires.
There is no hard and fast rule for that buzzword, cld, imho.
I think building a runner with a thicker plinth is a great starting point.
I used 1.5" aluminum plate for the first three I built. Once you build a plinth and mount a tone arm you can start to play music. This is where the fun begins. Reading add copy from tt manufacturers is a tough way to try and build a deck. I think of the tt as a system of elements. Creating a marriage is a roll of the dice. Sometimes it works and sometimes it doesn't. The R&D part of DIY is the fun. Oh, make sure the motor mount has enough clearance so it doesn't rub the plinth. I chased this noise for some time.
Thanks for sharing your experience! I'm hoping to learn from the experience of others. I think it was Mark Twain who said, "Experience is a hard school, but a fool will learn by no other."
Since you've done several Empires, what were the most successful plinth constructions & combinations for you? What tonearms have you run?
I've already damped the platter by filling the outer rim with a 3M DP-105 flexible epoxy containing bronze filings. I've also removed the lip for the 45 rpm adapter so that I can experiment with different platter mats.
On the more recent 598/698 Empires, the inner and outer platter material was composed of different metals with different resonant modes. When they are assembled together, they cancel each other out. I was hoping to achieve something similar in my plinth, such as by coupling my aluminum base plate to a steel sheet, and perhaps add damping via another material. Have you had any experience doing this?
Thanks again for your help!
"Knowing what you don't know is, in a sense, omniscience"
I've gone pretty much teres style with my latest. The replinths I've done for 208's have used dynamat as a beginning with the stock plinth. I've used dynamat cut in circles and stuffed under the platter to mitigate its ringing. I've made plinths of 1.5" aluminum plate and 1" phenolic..
I've used regarding arms originally but now have gone to a project 10cc evolution. Also have mounted kuzmas.
I've used natural gum rubber in 1/4" thickness for a "constrained" layer in my assemblies.
Sometimes the resonance can be desireable. I've noticed you can overdamp a mechanism too. Maximum damping may not be the goal. Damping tunability is a boon to the diyer.
Here's another Berndt creation. Started life as a Teres project. Platter, plinth and arm mount by Berndt.
How does it sound? That is subjective and also depends on the cart / arm but I would say it crippl'n.
That one sure looks nice.
Lots of heavy metal.
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