| 摘要 |
PURPOSE:To obtain a bias magnetic field with a specified polarity and amplitude with a comparatively simple constitution, by using a permanent magnet as a bias magnetic field generating means, detecting the magnetic field with a magnetism sensing element and rotating the permanent magnet in response to a preset value. CONSTITUTION:A permanent magnet 11 prolonged toward the radial direction of a disc is located at the opposite side of a pickup 9 of the disc 7 on a turntable 8. A bias magnetic field from the permanent magnet 11 is detected with a magnetism sensing element 12 such as a Hall element fitted to the tip of the pickup 9 and the output is applied to a comparator 16 via an amplifier 14. The value of the bias magnetic field required at recording is inputted to the comparator 16 from a bias set circuit 15, both inputs are compared and an error signal is applied to a driving circuit 17 for a permanent magnet driving mechanism. The bias magnetic field with a specified polarity and amplitude can be obtained through a permanent magnet driving mechanism 13. The device is comparatively simple. |
