YNWOAN,
Any chance that you could share the machine drawing with any of us? I understand that it is much more than just the mechanical drawings and also is a materials requirement to duplicate your turntable but that would be a start. Your design does look like it was very well designed and after 15 years it seems you have produced a very workable solution. I am interested in seeing how you implemented the magnetic repulsion suspension.
Steven
Any chance that you could share the machine drawing with any of us? I understand that it is much more than just the mechanical drawings and also is a materials requirement to duplicate your turntable but that would be a start. Your design does look like it was very well designed and after 15 years it seems you have produced a very workable solution. I am interested in seeing how you implemented the magnetic repulsion suspension.
Steven
I have built a number of magnetically supported bearings and 'trust me' 🙂)) none of them have exhibited any wobble. On the contrary, they have been remarkably stable, either lightly loaded or heavily loaded. I appreciate the validity of the point you are making, but the reality that I have experienced does not support it.
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Putting this issue aside (for now) the bearing can only be considered in detail once the weight of the platter is known as the compliance of the magnetic field must be considered.
What is, or can be, an issue with magnetic bearings is shielding. Not so much the need to use a non magnetic shaft - the field from the shaft is very minor compared to that from the magnets directly. The problem with shielding the magnets is that whatever you use it will itself attract magnets - like the ones inside ones MC cartridge - what you gain on the swings you lose on the roundabouts (or that can be the case). However, the horizontal dispersion of the field is relatively low compared to the vertical field and displacing the magnets from the surface of the platter will also reduce their influence - though this will raise the centre of gravity and may well bring problems of its own.
At the end of the day there really is no better solution than physically modelling the proposed solution and varying parameters.
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My comment regarding 15 years was with regard to mats - it's been more like 25 years that I built my first turntable and started to develop it. The turntable I now use did not spring whole from one set of drawings but has rather evolved over significant time. As a result, some parts were drawn out before I ever used CAD. As you say, material choice is very important.
With turntables, there is an element of science and an element of artistry. Whilst some aspects can be measured those measurements do not fully describe the sound. For example, changing armboard construction and/or material impacts upon the sound, but this is not easily measured and preference for one solution over another is a very subjective decision. On the other hand, relieving pressure from the thrust pad of the main bearing not only has a subjective impact but can also be seen to measure better.
What is your opinion on the best material for the armboard ?
I need one for a Thorens TD124 and am not sure what to choose.
I need one for a Thorens TD124 and am not sure what to choose.
In my opinion, the chassis/arm termination should have a high stiffness to mass ratio. In general I would say that the system should be critically damped but not over damped. In fact, applied damping should be avoided and I am not a fan of laminating different density materials together (as is popular with some designs). In my view, damping of this nature causes some frequencies to be significantly more steeply attenuated than others and leads to quite clear colourations - in general it is better to have a livelier, but quick, system than a heavily damped but slow one.
In the past it was popular for turntable designers to follow the design ethos of the closed loop. In this situation the theory goes that all parts are made as rigid as possible and therefore the resonant potential of all components is equal. However, the reality is that this level of conceptual rigidity cannot be achieved, particularly with regard to the main bearing - although the bearing can be made 'stiff' this will not be true equally across the spectrum. However, I have found, when implementing the magnetic bearing that a closed loop is not necessarily desirable - certainly the dynamic range and detail retrieval of my non-closed loop construction is of the first order.
When the stylus is modulated by the groove it generates electricity but this is not 100% efficient and a significant level of energy remains unconverted. Some of this will pass in to the record and some in to the body of the cartridge and then the arm and then the armboard/chassis. If a stethoscope is placed on the surface of an armboard when a record is playing (unamplified), you can clearly hear the music as it resonates from the surface of the armboard/chassis.
Sorry, I've got to do some work - back later probably.
I would use something light but stiff - my favourites have been a carbon fibre Nomex carbon fibre sandwich a carbon fibre laminate bonded with a viscoelastic compound and an aluminium arboard, anodised and joined in the same way (this is what I use now. the lower layer of the armboard is bolted to the chassis and the upper layer is attached to the arm. I would also say that how the armboard is attached (and how tightly it is attached) to the plinth/chassis also makes a difference.
Now I really must work - sorry.
So carbon fiber fixed to the plinth .. alu fixed to the tonearm .. viscoelastic stuff in between... what type of viscoelastic bond do you use ?
Err..no - probably didn't explain myself very well.
My armboard is constructed from two 3mm plates of aluminium (anodised). the two pieces are bonded together to form a true constrained layer structure. The arm is bolted to one layer and the armboard is bolted to the chassis via the other layer. Unfortunately, the board on my deck is based on another armboard/chassis that is a commercial venture in which I am involved and so not free to give all details (for the same reason I am not able to give full details regarding the magnetic main bearing - sorry). However, if you research constrained layer damping you will find that the thickness of the glue layer is relative to the thickness of the metal skins.
I also have exactly the same design and construction of armboard but made using 3mm thick carbon fibre sheet and another armboard made from a laminate of carbon fibre skins over a core of Nomex.
My armboard is constructed from two 3mm plates of aluminium (anodised). the two pieces are bonded together to form a true constrained layer structure. The arm is bolted to one layer and the armboard is bolted to the chassis via the other layer. Unfortunately, the board on my deck is based on another armboard/chassis that is a commercial venture in which I am involved and so not free to give all details (for the same reason I am not able to give full details regarding the magnetic main bearing - sorry). However, if you research constrained layer damping you will find that the thickness of the glue layer is relative to the thickness of the metal skins.
I also have exactly the same design and construction of armboard but made using 3mm thick carbon fibre sheet and another armboard made from a laminate of carbon fibre skins over a core of Nomex.
Thank you... it seems I reached a point where I can not get more info from you 🙂
Did you also experiemnted with phono stages ?
What cart are you using ?
Did you also experiemnted with phono stages ?
What cart are you using ?
As sq says, he is buildingme a Paradise phonostage (very nice job he is doing too); the paradise is the best phonostage I have heard (sq has already built two and I have heard both in my system).
The cartridge is a bit unusual because it is a black Linn Troika (a unique prototype sample - all production cartridges were red) - this has now been rebuilt and includes a ruby cantilever and Fritz-Gyger S stylus.
The cartridge is a bit unusual because it is a black Linn Troika (a unique prototype sample - all production cartridges were red) - this has now been rebuilt and includes a ruby cantilever and Fritz-Gyger S stylus.
Oswald Mill slate plinth, if I'm correct. Slate has been in vogue recently. Many agree to pay quite a price for the mass and not that easy treatment. While others advocate this material doesn't have neccessary damping properties as compared to panzerholz or other:
damping factor values : damping factor values
What's your opinion on that? Personally, I'm thinking about panzerholz for my L75 plinth.
damping factor values : damping factor values
What's your opinion on that? Personally, I'm thinking about panzerholz for my L75 plinth.
Materials like slate and marble have been in vogue since forever. Pure sonic poison if you ask me, even in a constrained layer. And many plinths simply bolt down the chassis on top of slate... which produces great bass i hear 🙂
Perceptions vary wildly. And looks do count.
It seems i only like minimal surface area plinths, so all the sculptures in wood and stone are out. A floating, decoupled subchassis changes this aspect considerably.
As others gave said, slate is very in vogue in certain quarters. I've done some experimenting with it and have not been convinced. Slate is. Often described by its advocates as being inherently well damped and a natural constrained layer construction - neither of these statements are true.
The only real advantage of slate is that it is relatively soft compared to granite and can be neatly cut with a water jet - looks nice too.
Most of the decks that use slate plinths cite it's mass as the reason that further isolation is not required; this is, in my opinion, nonsense. The problem is that people relate mass to themselves and it is common for people to write that a deck is 'so heavy I could hardly lift it'. Just because a person cannot lift something does not make it well isolated! Even the heaviest of turntable plinths is not that heavy in the greater context.
The only real advantage of slate is that it is relatively soft compared to granite and can be neatly cut with a water jet - looks nice too.
Most of the decks that use slate plinths cite it's mass as the reason that further isolation is not required; this is, in my opinion, nonsense. The problem is that people relate mass to themselves and it is common for people to write that a deck is 'so heavy I could hardly lift it'. Just because a person cannot lift something does not make it well isolated! Even the heaviest of turntable plinths is not that heavy in the greater context.
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