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In the Forum: Analog Playback
In the Thread: Rim drive?
Post Subject: Keep the magnetism in the cartridgePosted by Serge on: 4/29/2011
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 Romy the Cat wrote:
I do like the idea of magnetic suspension; I do not know why you feel that it is a stupid idea. As you built up the mass of your platter then very soon will not be able to hold the heavy platter at a single point bearing. The 20 point still cap sit on vertical bearing but 50 or 70 pound will not as the contact surface per mass ration will be too great. So, to use magnetic suspension in this scenario I fell is very cool idea. Pretend you have 100 pound platter but only 10 of them is being handled by bearing, the rest is elevated by magnet. I think it is an elegant solution as you would have high moment inertia combined with hard path to ground (important in my view).

Rgs, Romy the Cat


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.

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