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Old 26th October 2002, 02:27 PM   #1
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Default suspended deck

This is my first post here

Is anyone else building a suspended deck?

Here is a pic. of mine (hopefully)

It has-Rubber torsion suspension,natural frequency 1.2 Hz
Sandwich platter with PVC foam core,Glass/epoxy faces
Glass/epoxy box-beam sub-chassis
Balsa/laminate plinth
Scheu bearing
Cassette tape belt
Premotec motor,Manticore PSU
Stogi Reference arm

Richard
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Old 26th October 2002, 11:34 PM   #2
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Default Re: suspended deck

Quote:
Originally posted by supermodel
This is my first post here...
Here is a pic. of mine
Welcome. looks like an interesting TT. Have you dug into the DIY TT thread yet? Your experiences could be contributory.

dave
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Old 27th October 2002, 03:52 AM   #3
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Hi Richard,

Welcome to the forum.

Very interesting TT you have there, and I'd love to hear more about some of the design elements and the philosophy behind your decisions. For instance the suspension, platter, sub-chassis and plinth.

I'm in the midst of a radical rebuild on one of my SP10 MkII's at the moment, but am going down the high-mass contrained layed road. Estimated weigh is near 100kg plus stand.

Cheers
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Old 27th October 2002, 11:28 AM   #4
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Default suspended deck

Dave

Yes,I found this forum after the DIY deck thread was well under way,but read through it.It has real potential,but seems to be
dormant.Feel inclined to try a variation on the oil-bath.


Richard
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Old 27th October 2002, 12:31 PM   #5
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Default suspended deck

Brett
Looks like my approach is 180 degrees opposed to yours (and everyone else`s for that matter)
Playing around with this has convinced me that structural
efficiency rather than high mass is the best design philosophy.
Mass is not an energy sink as so many people believe.It stores
it and dissipates it slowly ,degrading sonics.
My platter weighs 2 kg,the sub-chassis 0.5kg.Using a very
compliant suspension,the objective is to expell kinetic energy
(bearing noise) through the lighter mass.This also benefits the
resonant behaviour of the platter,being excited by the stylus.
Also low platter mass means less bearing noise.

I do not believe that the platter should be designed as a flywheel.It needs to be stiffer (denser) towards the centre.
Superfluous mass at the periphery degrades it`s perfomance.
It is the task of the drive system,not the platter,to provide
speed stability.

The arm has to have a very stable relationship to the platter.
Seperate arm boards compromise this unacceptably.

Of course my deck has problems,associated with the suspension.
Rubber is subject to drift (creep) which means it has to be
adjusted frequently.Also,there is a lot of energy stored in it.
Stability is marginal.

This is all just my opinion of course.
Thanks for inviting me to air my views
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Old 27th October 2002, 02:15 PM   #6
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Default TT

Hi,

Your design ideas seem very interesting and I hope you succeed in building a worldclass design.

IMO however high mass certainly helps to relief the motor of its' burden.
Therefore I always try to go for a lower power motor to bring the platter up to speed.
Once that speed is achieved the motor can than idle along not having to interfere.
This way one gets a very quiet and stable TT.



Quote:
The arm has to have a very stable relationship to the platter.
I agree,you have to in a suspended design.

Quote:
Mass is not an energy sink as so many people believe.It stores
It is an energy sink.You need to know what you're doing though.

From what I see looking at your design you're relying on constrained layer damping through carefully choosen materials.
If this works for you then I'm happy with it.

Maybe you can find inspiration in the very lengthy DIY TT thread,although we there decided to leave suspension out of the equation for simplicity's sake.

Happy building,
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Old 30th October 2002, 04:03 AM   #7
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(Physics ain't my specialty so I'm standing to be corrected)

The way I see it:

The platter doesn't sink energy as you said, instead it dissipates it. To dissipate one unit of energy, you can either move a heavy load over a short distance, or a light load over a longer distance. The further the platter moves as it dissipates extraneous energy, eg vibration, the greater the noise that will be introduced, so I'd favour a heavy platter over a light platter.
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Old 30th October 2002, 12:32 PM   #8
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Default Platter clatter is less with the latter.

About the silliest stuff I ever saw a high end TT platter made of was glass. This stuff is very elastic and so would very poorly damp any vibrations. I never saw one made of lead though. Besides being super heavy (IMO that's good) it is very non resonant. Hit it with a hammer and it does not ring, it jusy makes a dull "thud" sound. It does not spring back to shape when it is deformed by a force like something springy does.

I agree that a rotating mass cannot sink energy. It can only store or release that kinetic energy by a change in it's rotational speed.

GP.
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Old 30th October 2002, 02:07 PM   #9
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Ever tried tapping/holding a med-lab centrifuge rotor ?.
The shape makes them dead in addition to the deadening in the material.

Eric.
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Old 30th October 2002, 02:17 PM   #10
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My CD transport's platform rests on 3 spikes. When I lift it up and hold it with my hands it sounds worse.
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