| 摘要 |
PURPOSE:To attain the stable control of the tone arm speed by detecting the tone arm speed on the basis of the variation of resistance value between an end of an elevation sheet and a contact member and separating electromagnetically the speed detecting part from a driving part to eliminate the effect of said driving part. CONSTITUTION:When a tone arm 1 moves within a horizontal plane, a roller 14 rolls on a sheet type resistor 17 set on the upper surface of an elevation sheet 16. Therefore the time change component of the a-c resistance value, i.e., a speed signal proportional to the moving speed of the arm 1 is led out to the output terminal of a differentiation circuit 19. This speed signal is fed back to a driving amplifier 11 to control the tone arm speed. For such a controller, a speed detecting part is electromagnetically and completely separated from a horizontal driving part. As a result, the time change component of the magnetic flux generated at a driving coil is never detected by a speed detecting coil nor fed back to the driving part. This improves the stability of the arm 1 when it has a horizontal shift. At the same time, a servo action of high accuracy is possible. |
