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Fisher mt-6225 motor design

Carbsandcaps

Carbsandcaps

Super Member
What do you guys think of the motor design on the fisher mt-6225 turntable? The perminant magnet it’s a strip around the playter and then the motor is on 1/4 of the table. I could be overthinking it but wouldn’t this be inconsistent? I guess since the magnetic strip is solid it will hold speed. IMG_2560.jpegIMG_2559.jpeg
 
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Nothing funny about this.
There is three coils thad drive the platter, where one is pulling on a nearby magnet -one of 120 poles-, one is pushing a one resting , and they alternate their action createing an even movement.

This is described in the service manuals og the various Fisher models..
The downside is possible cogging at the frequency of 120 poles divided by 1.8 second per revolution = 66.67 hz. This is detectable on my Fisher mt-6330 , listen with a stethoscope to the chassis/arm while turning the platter at about 33 rpm of faster and you may hear it. other motors have less poles and cogging frequency will be below audible range. 13.33 hz for a 24 pole motor..

Apart from that the motor designs and drive electronics are very clever.
 
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