What about the Plinth?

Re: What about the Plinth?

Postby theeng » Tue Mar 24, 2020 7:23 pm

Brock,

The machineability of Aluminum is shown here, http://www.howardprecision.com/wp-conte ... erties.pdf, but this some what contradicts the discussion, https://materialsdata.nist.gov/bitstrea ... Allowed=y;

However, I just checked, and a 2" thick piece of ATP-5 22" x 25" is about $300, much cheaper than 6061-T6, but a similar dimensioned MIC-6 cast plate is $960. Not sure why the ATP-5 is so cheap? I would talk to the machine shop and ask them what aluminums they have worked with, but if they have or can work with the ATP-5, then the whole new plinth concept may not be so far out.
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Re: What about the Plinth?

Postby Brf » Wed Mar 25, 2020 10:16 am

Tirebiter wrote:Oh my...that sounds interesting Brent! A couple of questions; are the feet up to the task of supporting all the extra weight? Shape? Is the TNT rectangular footprint ideal or is something else preferable? You had mentioned that the geometry of the feet was important. I would just as soon keep things simple but if there are some additional tweaks that would help then I would be open to suggestions.


If this was my project, I would simply duplicate the original TNT plinth design to ensure compatibility with the rest of the TNT parts. One consideration would be to eliminating the removable armboard to create a "hotrod" plinth. This would also cut down machine cost but limit future flexibility with tonearm choices. As for the additional weight of the plinth, both the existing sprung "T" or "elephant" feet can be easily modified to support the extra weight. Ball or air suspension will not be a problem.
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Re: What about the Plinth?

Postby Golear » Wed Mar 25, 2020 2:53 pm

If you're going for an entirely new plinth design, then how about curvy shape, where each radius is a prime number, a Fibonaci number, or a Golden Ratio, perhaps? Ditto for the distance from pivot to each of the feet. Oh yes, and the thickness could be varied, too.

I think there are CAD programs that can calculate vibration modes, too. Does anyone in the forum know how to do that?

Or:

We might borrow a technique that is used on the LIGO and Virgo telescopes. Instead of trying to avoid all resonance, or trying to damp each one without that having unintended consequences, they arrange their apparatus so that all the resonances come together. (I know... "You're going to do what?"). ....And then they apply critical damping on that single frequency. They use lasers to detect the movement that is caused by the resonance. I don't know what actuators are used to apply the counter movement.

For a turntable, the resonant frequency could be detected by another cartridge that is resting on the plinth. And then for actuator... may be we can use a speaker? We take the cartridge output, put it through a filter that only allows our resonant frequency through, amplify it, then connect it out-of-phase to the speaker assembly. Totally analog. When the resonance stops, the speaker also stops. The speaker can be an infinite baffle design that has its resonance frequency at the resonance frequency that we are looking for.

PS: The LIGO and Virgo gear suspends the mirrors off a frame, via quartz thread (because it has the least "give"). When a vibration wants to move the frame, the inertia in the mirror naturally resists that movement. I don't know if that may be relevant for a turntable.
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Re: What about the Plinth?

Postby Tirebiter » Wed Mar 25, 2020 8:50 pm

Brf wrote:
If this was my project, I would simply duplicate the original TNT plinth design to ensure compatibility with the rest of the TNT parts. One consideration would be to eliminating the removable armboard to create a "hotrod" plinth. This would also cut down machine cost but limit future flexibility with tonearm choices. As for the additional weight of the plinth, both the existing sprung "T" or "elephant" feet can be easily modified to support the extra weight. Ball or air suspension will not be a problem.


Thanks Brent, makes sense to keep it simple though I may substitute the curved drive cutout for the square. I also like the thought of eliminating the cutout for the armboard. I will have to deal with the SME mount for my tonearm but the machining will still be less complex. Good stuff!
TNT Jr, Graham Phantom III, ZYX Universe II LOMC, Tempo Electric Silver Phono Cable, Amazon B-lab Phonoamplifyer, Lamm LL2 Pre , Lamm ML 2.1 Monoblocks, Avantgarde Duo Grosso....and a Thorens TD 160 Mk I in standby....
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Re: What about the Plinth?

Postby MMMC » Thu Mar 26, 2020 4:36 am

Tirebiter,

If it's not too much of a hassle, before you take everything apart, do you mind posting an overhead photo shot of your table as is, that captures the tonearm mounting, and one photo of the underside of your table. If the photos create any hassle, please don't do it. I like the direction BRF was alluding to of a simple stiffer sandwich construction by employing a thicker aluminum "plate" which may be less work. A sort of "Hot Rod" TNT plinth. All of the cutouts could possibly be performed at the machine shop. The thicker plate also becomes part of the table appearance, similar to the Aries. I do not have an engineering degree, just ideas floating in the brain.

MMMC
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Re: What about the Plinth?

Postby Mr_Putty » Thu Mar 26, 2020 11:38 am

Tirebiter,
Sounds like you are up for a challenge. RED FLAG ALERT, I have NOT done this but suggest it can be done. The cheapest possible soft metal plate construction could be done this way. Make a template of the shape you want out of plywood. And use a carbide router bit in a hand held router to cut the outline. You would limit the depth of (probably many) cuts to approximately 1/16 inch. This is never recommended in wood working because its probably too dangerous! And NOT for the inexperienced. You need to know what you are doing and protect yourself. I only suggest it as this is probably what I would do if I ever get around to it, AND still think its a good idea. Two other ideas. Use a CNC machine to do the cutting. They are getting pretty common. Or find someone with a water jet cutter and have them do it. As usual all it takes is the right number of $$$ and someone will be willing to do what you want.
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Re: What about the Plinth?

Postby Tirebiter » Fri Mar 27, 2020 1:08 pm

MMMC wrote:Tirebiter,

If it's not too much of a hassle, before you take everything apart, do you mind posting an overhead photo shot of your table as is, that captures the tonearm mounting, and one photo of the underside of your table. If the photos create any hassle, please don't do it. I like the direction BRF was alluding to of a simple stiffer sandwich construction by employing a thicker aluminum "plate" which may be less work. A sort of "Hot Rod" TNT plinth. All of the cutouts could possibly be performed at the machine shop. The thicker plate also becomes part of the table appearance, similar to the Aries. I do not have an engineering degree, just ideas floating in the brain.

MMMC


MMMC, no hassle at all, in fact I was going to document the project with photos start to finish and will post when things get going.

Mr_Putty wrote:Tirebiter,
Sounds like you are up for a challenge. RED FLAG ALERT, I have NOT done this but suggest it can be done. The cheapest possible soft metal plate construction could be done this way. Make a template of the shape you want out of plywood. And use a carbide router bit in a hand held router to cut the outline. You would limit the depth of (probably many) cuts to approximately 1/16 inch. This is never recommended in wood working because its probably too dangerous! And NOT for the inexperienced. You need to know what you are doing and protect yourself. I only suggest it as this is probably what I would do if I ever get around to it, AND still think its a good idea. Two other ideas. Use a CNC machine to do the cutting. They are getting pretty common. Or find someone with a water jet cutter and have them do it. As usual all it takes is the right number of $$$ and someone will be willing to do what you want.


Mr Putty...as I have decided to go for broke by using 2" plate the route I will be taking is to use a machine shop. If I were going the 1/4" plate route I would likely have tackled it myself and applied your suggestions. Much appreciated regardless.

Golear wrote:If you're going for an entirely new plinth design, then how about curvy shape, where each radius is a prime number, a Fibonaci number, or a Golden Ratio, perhaps? Ditto for the distance from pivot to each of the feet. Oh yes, and the thickness could be varied, too.

I think there are CAD programs that can calculate vibration modes, too. Does anyone in the forum know how to do that?

Or:

We might borrow a technique that is used on the LIGO and Virgo telescopes. Instead of trying to avoid all resonance, or trying to damp each one without that having unintended consequences, they arrange their apparatus so that all the resonances come together. (I know... "You're going to do what?"). ....And then they apply critical damping on that single frequency. They use lasers to detect the movement that is caused by the resonance. I don't know what actuators are used to apply the counter movement.

For a turntable, the resonant frequency could be detected by another cartridge that is resting on the plinth. And then for actuator... may be we can use a speaker? We take the cartridge output, put it through a filter that only allows our resonant frequency through, amplify it, then connect it out-of-phase to the speaker assembly. Totally analog. When the resonance stops, the speaker also stops. The speaker can be an infinite baffle design that has its resonance frequency at the resonance frequency that we are looking for.

PS: The LIGO and Virgo gear suspends the mirrors off a frame, via quartz thread (because it has the least "give"). When a vibration wants to move the frame, the inertia in the mirror naturally resists that movement. I don't know if that may be relevant for a turntable.


Golear, the idea of changing the shape of the plinth is intriguing but I rather like the simplistic lines of the TNT so have decided to keep costs down by going with the known design. I figure that if it sounds terrible then an option would be to take the plinth back for additional mods. It would be very interesting to delve into the technical side of the dissipation of various vibrational frequencies.....
TNT Jr, Graham Phantom III, ZYX Universe II LOMC, Tempo Electric Silver Phono Cable, Amazon B-lab Phonoamplifyer, Lamm LL2 Pre , Lamm ML 2.1 Monoblocks, Avantgarde Duo Grosso....and a Thorens TD 160 Mk I in standby....
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Re: What about the Plinth?

Postby Brf » Fri Mar 27, 2020 1:21 pm

Tirebiter wrote:
Mr Putty...as I have decided to go for broke by using 2" plate the route I will be taking is to use a machine shop.
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Re: What about the Plinth?

Postby MMMC » Sat Mar 28, 2020 2:55 am

Tirebiter,

WOW!!!
..........as I have decided to go for broke by using 2" plate the route I will be taking is to use a machine shop. If I were going the 1/4" plate route I would likely have tackled it myself and applied your suggestions. Much appreciated regardless.

Go on with your bad self!!!
My HRX plinth is a bit under 2". You must be more than just a little excited, because I am, and it's not even my turntable!!! Looking forward to your photo chronicle of the project when completed. BTW, I think you and I are the only two on the Forum with a ZYX Universe II riding on their tonearm. It's tunnel vision now for you, until completion.

MMMC
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Re: What about the Plinth?

Postby Golear » Sat Mar 28, 2020 2:31 pm

Good luck Tirebiter.

By the way, check out the Rega RP-10.
http://www.theaudiobeat.com/equipment/rega_rp10.htm

I've heard the RP-10 and it's stunningly good. I think Rega has a really good idea with their ceramic material and irregular shape. It's super light, but very rigid. It's weird handling it. My brain expected something that light to be flimsy, and something that rigid to be much heavier.
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