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Lenco plinth? How big is too big?

I have an L78, upgraded Origin Live One arm, Empire MC-5 moving coil cartidge, and access to a sawmill with lots of prime cherry wood. I was thinking of a cherry plinth, 17 inches wide, 24 inches long, and six inches tall of cross layered one inch cherry. Then cut off the rear corner where the tone arm is mounted, in a sweeping arc of about 10 inch radius, and mount the tone arm on that detached corner. Use 1 inch thick isomolded graphite disks of 2 inch diameter topped by one 3/8" tungsten carbide ball, and resting on three such balls. Use three of these ball/disk combinations for each of the main plinth and the corner with the tone arm. What do y'all think? I would appreciate any suggestions before actually putting it all together. Thanks. Ralph
ralph1223
pryso
1,928 posts
 
Lewm, I had the same impression from Ralph's arm mount description and the same sense of caution.

In ongoing design for my SP-10 plinth, I'm intending to bolt down the armboards (2) with brass machine screws. Each armboard will be 3/4" thick and replace that section of the top 3/4" layer of birch ply. The idea of cutting off the end of the plinth then reattaching the arm somehow sounds questionable to me.

Ralph, concerning how big, you might want to read some of Jonnantais' experiments with various plinth materials and size.
mosin
410 posts
 
Lew,

I am probably in the minority here when it comes to the issues surrounding tonearm coupling. I do believe that mounting the tonearm to the plinth in a secure way is indeed the only way to go, but I stop short of your comment regarding an interaction with the bearing. Still, it should be a non-compliant mount, in my opinion. All this begs many questions about isolation, neutrality and what it all means. It also goes to the issue of dissimilar materials in the build. Should that apply only to the plinth? I don't believe so. What I do believe is that every small part, and how that part is applied, counts. I also believe there are various ways to get there, and in the end very different turntables can reach the goal. It is a very complex process, and there are no fast answers...unfortunately.
lewm
13,019 posts
 
Win, I probably overstated the case for tonearm coupling. As you know, there ARE those who do advocate firm coupling to the bearing. However, your opinion carries a lot of weight with me (at least 200 lbs of slate). Anyway, I think we both agree that mounting the tonearm completely outboard of the plinth is not optimal. Like Pryso, I am also building an SP-10 plinth, so these considerations are very much on my mind, too. Ralph, I hope you get the picture.
jloveys
226 posts
 
So if I understand the utility of a good TT plinth is to damp vibrations as much as possible. Layers of different materials and added weight/size matters to achieve good damping. Nature of materials too.
bornin50
32 posts
 
I think Ralph has left the building. :)

The purpose of the plinth is to support the deck in a user friendly, high waf structure, and prevent unwanted vibrations (from inside or out) reaching the stylus. Use minimum 6 layers of 18mm ply or 30mm of slate. :)

Rgds
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