Denon DR-370 motor rear cover

About this part

The motor used in the DENON DR-370 is of type HA1-7. At an AC 100 V supply, it runs at 1500 rpm with a 50 Hz supply and at 1800 rpm with a 60 Hz supply; its speed is thus kept constant in accordance with the mains frequency. After the motor ages, its housing becomes very hot during operation, and the motor may randomly enter a locked-rotor condition, causing the stator coil temperature to rise sharply and creating a constant risk of burnout. The cause is that the rotational resistance of the rotor's front and rear bearings is high, which increases the load on the motor. The front bearing can be cleaned and then lubricated with a few drops of oil, but the rear bearing can only be cleaned and lubricated after the rear cover has been removed. However, the rear cover is made of a zinc alloy and cracks very easily when pried off. The internal design of the rear cover is relatively complex, and the damping felt ring inside it is the main cause of the high rotational resistance of the rotor. If the damping felt ring is removed, the rotor's front-to-back play becomes too large and cannot be adjusted. We therefore redesigned the rear cover with a more rational, simpler, and more reliable structure and had it made of brass. Although the manufacturing accuracy requirements are very high and the production process is complex, the final result is that the rear cover works well once installed on the motor, the motor's operating temperature has dropped by about half, cleaning and re-oiling will be very convenient in the future, and the rotor will no longer lock or seize.

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