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Tone Arm board material

My VPI Ares3 turntable which is made with a laminated acrylic/aluminum/acrylic plinth, about 2.5 inches thick in total, has a 5/8 inch circular cut through the top layer of acrylic which exposes the center laminate of aluminum.  Set into this circular cut out is the 'puck' arm board mounting disc which is about 7/8 inches thick acrylic.  This bolts to the aluminum via three machine bolts.  My SME Series IV magnesium tone arm is bolted to the acrylic tone arm puck.

Magnesium is known for its superior vibration and sound deadening qualities, so I was wondering if anyone has any thoughts on making the tone arm board 'puck' out of solid magnesium vs. the factory supplied acrylic??  I can see why they probably don't use magnesium as it's super expensive.  I just got a quote on a small piece of magnesium to machine a new tone arm board and its $125.  But if it were to make an improvement in performance, its cheap money.

Does anyone out there have any thoughts on this?

128x128slimpikins5
atmasphere's avatar
atmasphere
11,574 posts
 
The plinth of the turntable should be as dead and rigid as possible.

The thing that most people don't think about is that the arm board is part of the plinth. The base of the arm should couple as rigidly to the bearing mount of the platter as it can. If the arm board is made of a different material than what supports the platter bearing, its possible for vibration to move the platter on one plane while the base of the arm is moving in another or maybe isn't moving at all.

You want the base of the arm and the base of the platter bearing to move in the same plane at the same time or else the difference is interpreted by the pickup as a coloration.

IME for this reason the arm board should be the same material as the structure that supports the base of the platter bearing and hopefully that is the same structure that supports the arm board too.
pryso
1,903 posts
 
sleepwalker, when I began researching plinth building I found a few suggestions for Corian.  However I then read that Corian can in fact be subject to vibration transmission.  Otherwise it might be more commonly used I guess.  One comment stated that transmission will vary depending on the amount and size of the aluminum particles in a given Corian sample.

It may look nice and be easy to work with, but I ask myself if it is so good why is it not more commonly used?

Regardless, I think Ralph offered very good basic advice.
noromance's avatar
noromance
9,404 posts
 
My slate plinth builder supplied mine with wenge armboards saying it was the best he'd heard.
slimpikins5's avatar
slimpikins5 OP
191 posts
 
Thank you Atmasphere for the thoughts on materials used.
My Ares3 is Acrylic sandwiched with a center layer of aluminum.  The top layer of acrylic was machined out down to the aluminum layer so that the same acrylic material used for the arm board  is bolted directly to the aluminum.  In other words, the arm board is the exact same construction and materials as the plinth which mirrors what you stated.

I will stay with  this for sure (after the turntable does sound fabulous) and why fix what is not broken.


fsonicsmith's avatar
fsonicsmith
931 posts
 
While I don't claim to be an expert, I nonetheless agree with Ralph. I am not new to plinths and armboards. If possible, mount the arm directly to the base of the plinth. This is not possible with a Thorens TD124 unless the armboard chassis is cut off, but it is easily done with a Garrard 301/401 or an SP10. It surprises me that so-called state of the art plinths by some vendors have pivoting leaf armboards. Clever and versatile yes. Ideal, no. 
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