| 摘要 |
PURPOSE:To adjust a loop gain to an optimum value where the tracking shift is least, by providing a gain varying means which set the loop gain to a specified value and adjusting the gain so as to keep a frequency at gain crossing point constant. CONSTITUTION:A voltage at an output terminal of an operational amplifier 15 is measured while executing tracking, when the reproduction of a new disc is started or a reproduction stylus 4 is replaced. When a voltage exceeds 1 Vpp, the gain at 1kHz exceeds 1 in the frequency characteristics of a tracking circuit, so that the servo operation is made unstable, then terminals 16a and 16b of a switch 16 are connected and adjusting is made so that the loop gain is decreased. When the voltage is <=1 Vpp, the gain at 1kHz goes to <=1 and the servo operation is made stable, but since the gain of frequency at about <=100Hz is low, the terminals 16a and 16b are connected to increase the loop gain. |
