Magnetic bearings

The magnetic bearings myth

At first sight - magic: A magnetic bearing with no physical contact and no friction! But I am sure you have held two magnets together and then tried to hold them apart at a fixed distance while the opposite forces were acting on each other. It’s a difficult task and almost impossible to keep the distance constant for any length of time.

Now imagine a magnetic bearing where the shaft must be kept stable in its exact position without moving off centre while rotating. This is impossible to achieve with ordinary magnets. To achieve this you would need to monitor and continually adjust the exact shaft position, as the electromagnets forces are constantly changing. This would require a very sophisticated magnetic bearing system costing 10.000 dollars and which is used in very precise machines and which radiates a strong magnetic field.

But we can make a simple magnetic bearing when the platter is levitated vertically and a classic sliding bearing holds the shaft in a vertical position. In this case there is no contact in a vertical direction, but the platter will behave as if it is being supported on a spring- it will bounce up and down. This is because magnetic force acts exactly like spring – the smaller the distance the bigger the force and vice versa.

The practical solution is for the magnet to hold the platter up while the bearing shaft is still in contact with the trust pad but, due to magnetic lift, platter mass create less force on bearing thus making less wear and vibration. This method was first introduced in mid 60ties on the Stanton turntable where the magnet force ‘lowered the pressure' on the vertical bearing of the platter.

How the platter bearing is designed and executed, regardless what trust force is applied on the trust pad, is most important. A good bearing should have minimal noise and friction and, at the same time, the shaft should not wobble in the bearing housing. In practise it is better to have less weight on the bearing, even though less weight might cause the platter to move up and down due to vibrations in the bearing.

If there is a strong magnetic field below the platter it can effect the record and the cartridge.

Demagnetisation of records does improve sound dramatically -just try the Furutech machine.