The necessity of a plinth

Dazzdax, You raise an interesting question, and I am glad that Raul responded with his experience. One logical reason for a heavy plinth on the SP10 was put forward by Mark Kelly, a person whose opinion commands respect. Mark noted that because of the torque of the SP10 motor and that of other tts with torque-y motors, a heavy plinth will serve to counter the tendency of the motor to twist itself and the chassis frame to which it is attached. I have thought about this a lot; I am not sure how or whether high torque motors would create an audible problem, once the platter is up to speed. (The full torque of the motor is only applied during the instant after turn-on when the platter is still at rest, I would think.) Albert Porter's plinth deals with motor/bearing vibration in a novel way that might mitigate the need for a super heavy plinth. (Go to the Sound Fountain website to see a depiction of Albert's idea.)

Hi Raul, I didn't know that. I thought a custom made plinth is a necessity with the SP-10 to sound great. Stock SP-10 is very good, but SP-10 + custom plinth = great. But now you are saying a bit the contrary and it's an eye opener for me. Do you also concur with the hypothesis that a plinth can actually add coloration (or drain away the life out of the music)? In this regard Thom Mackris is quite right: it takes a lot of expertise to design a dedicated plinth/base that brings out the best of the turntable without the draw backs (there are many variables to deal with: mass, dimensions, materials, structural design, attachment of the turntable to the plinth, etc.).

Chris

I previously posted a question on the need for a massive plinth for the SP-10 on a couple of sites but did not receive any definitive replies. While there is extensive information of plinths for Garrards, Lencos, Thorens, and other rim-drives, there is not nearly as much for Technics or other quality DD tables.

My premise was that because of the mass needed for rim-drives, most DD owners assumed that would benefit their tables as well. But now we have more information and extremes are reported. At the low mass end is Raul who's SP-10 utilizes only an extension for arm mounting and three suspension feet, while the high mass approach is represented by Albert Porter and Oswalds Mill, among others.

So obviously both approaches can work. Too bad no one has reported on a direct comparison.

Here's the way I try to think of the difference between an idler and a DD as regards plinth design: In the idler, the motor and idler itself are "external" sources of noise and vibration, whereas the rotation of the platter and the bearing can be just as inherently silent as that of a belt-drive table. A high mass plinth can drain away the motor/idler noise before it reaches the platter/bearing. That makes sense to me. On the other hand, in a DD table, the motor is a priori and inseparably associated with the bearing/platter. In a way, it's a closed system. So it is not obvious to me how a high mass plinth per se can efficiently interdict the transfer of noise to the platter from the motor. That's why I admire the thinking that has gone into Albert's plinth; there is an attempt to drain spurious noise into a heavy iron block via a threaded rod that contacts the base of the motor/bearing assembly. So instead of going upward into the platter, the spurious motor and bearing vibrational energy has a low impedance path downward into the iron block. In theory, it makes a lot of sense and similar strategies could be adapted to other DD tables. The high mass plinth may just be icing on the cake, to dampen chassis vibration and provide a solid base for the total structure. (I guess other plinth-makers have used a similar strategy to Albert's; I am not assigning a patent on the idea.)

Hi Lewm, the idea of dampening of spurious vibrations is a nice one, but you actually don't need high mass to accomplish this! What you need is a low impedance path for the redundant kinetic energy, which should have a constraint layer construction. Such a construction is not by definition high mass --> look at the theory behind the Symposium Ultra Platforms.

Chris