Gentlepeople.
The debate between those that like compliant type supports and those that go for the hard supports has raged on forever. My view is that if you have a suitably still shelf, hard is the way to go. From reading here it seems that those that prefer hard supports make them all out of the same material. I believe that this arrangement can be improved, if your goal is to wick energy out of the TT structure. By using, say, three identical hard feet you are creating multiple paths to the shelf (ground). This is the electrical equivalent of an earth loop. I have experimented with identical and dissimilar feet on my TT and have settled with one fixed using a tungsten carbide ball, and two adjustable using large PVC discs. The PVC discs are softer than the plinth material and in theory tend to slow and impede transmission. The single TG ball is fast and creates one clean path to ground.
Just another view on things. |
Hi.
Typo in my last post. Please substitute the word "mechanical" for "electrical".
Thanks |
Halcro.
My TT uses one fixed duralium foot with a central tungsten carbide ball which contacts the shelf. This gives a point contact much like a spike. The other two feet are PVC discs 80mm in diameter with a rebate such that the circumference only touches the shelf. These are adjustable. See a pic on my web site www.krebsupgrade.com
The triangular TT where you can see the adjustable feet.
My view on this is that having multiple paths to a mechanical earth creates a smearing effect that is clearly audible. "Earth loop" was perhaps not the correct description. The common electrical paradigm is that a component must have only one path to earth. My view is that the same holds true for mechanical systems.
So, yes, if you use spikes only one should have direct contact with the shelf (earth). The other two should be coupled to the shelf with a slightly softer material than the spike itself. I am not advocating anything that would be considered compliant here, just something softer than the spike, maybe a hard plastic.
Simply another point of view.
Thanks.
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Halcro.
Part 2.
The same reasoning would suggest that there should be only one path from the LP surface thru the chassis, shelf, to the tonearm and on to the stylus. Your present iteration has more.
Thanks. |
Another design philosophy that one might consider is to minimise the number of joins and material changes, hence transmission speeds, between the LP/platter interface, around the loop to the arm and cartridge/stylus. Empirically it would seem to make sense that a join between dissimilar materials could do some damage to the integrity of this loop. This could include CLD techniques which, while very effective, should be implemented with this in mind.
Something for consideration? |
Chris.
Like your Alpha leg analogy. Actually, with the other two feet, we are trying to block energy transmission as much as possible although in practice I doubt that this can truly be done. The PVC feet are softer than the plinth and the shelf, acting like a road block.
I have tried this approach on all of my home brew and some commercial TT's, it doesn't seem to matter if there is weight asymmetry.( That said, my current triangular TT is virtually weight symmetrical) In all cases IMO, the one spike and two "feet" arrangement was better than 3 spikes. A trend is that, for a conventional plinth type TT, the spike goes close to where the tonearm is. I don't see any issue with energy build up in a suitably rigid, hard chassis.
The idea is to get mechanical energy out of the system quickly and cleanly.
Also I don't think that there would be any issue with this approach on an air or magnetically levitated platter.
No figures to back all of this up. Just listening.
Cheers.
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Yes the concept works. I used it in my first Home built TT, back in the late 70's. The idea was borrowed from an ancient Gyro testing table I saw at Air NZ. It had adjustable feet with wooden pads connecting the floor and one fixed cast iron foot. Cast in one piece into the chassis.
I asked my supervisor why?
His answer "to keep it still"
The table must have been 20 years old back then. Meaning the concept is at least 50 years old.
My comment about not truly working was around the " road block" probably not being absolute. There is likely some leakage thru the softer feet.
Cheers. |
Hi.
The Gyro testing table had 6 cast iron legs. Five of them were height adjustable with wooden decoupling pads. The sixth leg had no adjustment and it directly coupled with the concrete floor. |
Halcro.
You are using a plinth.
It is the shelf upon which your TT sits via the spikes you are using.
It would also seem logical that different shelf materials, size, shape, support method, spikes, et el would make a difference. |
Halcro.
We are both blessed with having music rooms that have concrete floors sitting on mother earth.
My definition of a plinth is likely a little wider than yours. To me it is.. "the structure that maintains accurate dimensional stability between the record surface and the tonearm". I am sure that you will agree that dimensional stability in this area is critical. I have also called this structure a "loop" in an earlier post.
By that definition your very nicely built stainless steel motor support, the shelf(or floor) and the equally nice arm pod are all parts of the plinth.
It would be reasonable to expect a change in the sound, if you were to change the stainless steel support for say a large diameter cardboard tube. Likewise we could expect a change in sound if the arm pod was made from say balsa wood. I suspect that your choice of these materials was based on experience and sound logic.
Since substitution of different materials would likely alter the performance, it can be inferred that your "plinth" does have a sound. |
I currently have a L07d in a thousand pieces. It uses extensive complex shielding around the motors many parts. Quite necessary I think, since the coils are close to the upper platter surface and are oriented vertically, focusing their flux up and down as opposed to horizontally on some other designs.
Chris, the increase in flux strength on the SP10 MK2 when stopped is due to the brake solenoid. Powered at stop, off when running.
I don't bother with the brake at all, using the EM braking of the motor itself to pull down the platters speed at stop. |
Lew
The shielding on the L07d looks like galvanized steel sheet. I think that it improves with the addition of extra shielding because there are some gaps and that in this case more is better. Yes it does resemble a flying saucer in profile and is , almost, completely encapsulated in shielding.
Another interesting design is that extensive shielding is used below the motor.
Btw it is not my intention to criticize the design. It is simply a different approach to building a motor.
I very much like its speed sensor approach and the clever way the main rotor magnet relieves some of the platter weight from the thrust bearing. |
Halcro
Is there a secondary issue here?
" ..a low frequency drone begins and then increases in volume.."
Could there be acoustic feedback following the initial EMR problem?
Cheers |
Halcro
Have you tried testing the resonance characteristics of the granite pipe?
The material does have a tendancy to ring like a bell.
Also by "identically situated" do you mean that you placed the Raven at the same place on the shelf as previously occupied by the Victor?
Does the Raven have a suspension?
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