Plinths for springy turntables?

[Rothchild]

I want to try building a new plinth for my Systemdek iix900, mostly for aesthetic reasons but obviously if there's a chance to improve it in the process then that would be great.

I'm interested to know what engineering considerations there are in doing something like this. The basic principle is very easy, the plinth is basically the motor mount and should (I presume) therefore minimise / absorb / disipate any vibration from the motor so it's not tranfered through the springs to the subplatter / armboard assembly.

In terms of the top plate of the plinth (that the motor mounts to) would it be better for this to have more mass or not? should it have some 'give' to allow vibrations to be transmitted out and down through the feet, what other considerations / engineering approaches / physics should I be considering when I select my materials for this?

[Rothchild]

For instance what would likely happen if I decouple the top plate from the frame (with sorbothane or similar) and made the frame quite massive and point loaded it to the shelf? Would suspending the top plate in this way help minimise the motor vibration to the main suspension springs?

[Reffc]

There's a danger that you can over-think these things. If the motor is suspended, the idea is to isolate motor vibration from the chassis. The last thing I'd suggest is beneficial is then to mount the chassis board to anything springy which will just amplify whatever vibration gets through (or act as anothe spring with its own resonance points) and transmit it to the arm (if not separately decoupled). There's two fairly simple ways I can think to approach this. First one is to bolt the chassis plate to something good and solid (high mass) and couple that to the ground or wall via a solid support. Transmitting what energy gets through like this both sinks and damps the energy transferred. The other way is to mount the motorboard or top plinth on sorbothane which converts the vibrational energy to heat energy. I use this useful property of sorbothane on my own 301/401 plinths and it works well. It minimises the energy transferred to the bearing and therefore to the platter and stylus. You have to use the correct grade and size though for the mass being paced on it, and it pays to have the mass equally distributed too. Some argue that mounting the motorboard this way allows independent movement between plinth and armboard (that motor vibration causes the movement) but it does seem to work and does clean up the sound.

[The Barbarian]

Marc {Rothchild}
Sometimes it's just not worth farting about, buy something different.

[Rothchild]

The other way is to mount the motorboard or top plinth on sorbothane which converts the vibrational energy to heat energy. I use this useful property of sorbothane on my own 301/401 plinths and it works well. It minimises the energy transferred to the bearing and therefore to the platter and stylus. You have to use the correct grade and size though for the mass being paced on it, and it pays to have the mass equally distributed too. Some argue that mounting the motorboard this way allows independent movement between plinth and armboard (that motor vibration causes the movement) but it does seem to work and does clean up the sound.

Thanks Paul,

This is pretty much what I was thinking of and tried to articulate above, I guess I actually have some scope for experimentation here as I can make it up with the sorbothane dampers and also test taking them out and screwing the board to the pinth too. I'm not too bothered about movement between the plinth and armboard as I'm reckoning that it'll be happening below a threshold where it might make any difference to the traction that the belt has to the subplatter, and that's the only point they're connected. As long as the armboard doesn't move relative to the bearing (which it can't as they're all part of one 'solid' assembly I should be golden, right?