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In the Forum: Analog Playback
In the Thread: Rim drive?
Post Subject: Not necessarily.Posted by Romy the Cat on: 4/29/2011

 Serge wrote:
It's silly because the minuses outweight the pluses. In order to suspend the heavy disc constant magnetic field should be strong. This field will easily travel through the platter, since the platter is by definition non-magnetic. MC-cart will be actually moving across this constant magnetic field which will generate current in the coils, law of physics. This current will be uncorrelated to the audio signal generated by groove modulation. This is obviously bad.
Consider also that the 'constant' field from a permanent magnet is non linear (related to distance) in practice and will also cause some resonances between its 'springiness' (inductance in electronics) and platter 'mass' (capacitance).
So IMHO outwardly the magnetic suspension is nice but does not hold to further examination.

It is not necessarily true. Of cause no one wants to inflict cartridge by a stray magnetic flux but do you insist that it will?

The field from a permanent magnet is linear. It varies with distance but distance varies with mass. So, as platter sit on an array of magnates then it will self level itself and if there is no further vertical movement then it will be in very stable magnetic condition.

Now, let see what we have with magnetic field affecting cartridge. Your feeling that magnetic field should be strong I think is incorrect. The magnetic field shall be very week. My relatively heavy Micro 8000 platter is suspended by air but my compressor that pumps the suspension air is EVRY week (very small aquarium pump). Since the air is distributed across large surface of platter then there is no need for high pressure. The very same is with magnets. I see the magnets to be VERY week, not to mention that they might be focused with not a lot of stray magnetic fields. Do not forget that you do not need to levitate the platter 10” in air but just rise it for 1mm or juts unload the mass of the platter for let say 80%. So, I think that leaked magnetic forces, if any leek even takes please, will be so week that when it reaches cats if will be at the level of background magnetic noise.

I think it is very simple to measure the influence of the platter magnates to the cartridge. I never had magnetic TT but I am sure the people who do it measure it and take actions that the stray fields are not a problem at all. What I am saying is that if the magnetic fields would affect the cartridge and tonarms in any meaningful ways then no one would make the magnetic suspension on TT as the negative impact is VERY simple to detect. BTW, I do have magnetic suspended tonearm, I did not see any magnetic related problems with it. The tonearm sound like shit but not due to the magnets…

The Cat

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