PURPOSE: To facilitate to reduce the scale of a circuit without putting a focus error signal into disorder by switching the reproduction level of a preamplifier when a device is switched from a reproduction mode into recording and erasure modes.
CONSTITUTION: When the signal of an optical disk is reproduced, switches 7, 8 are operated so as to turn OFF, and when the signal is recorded or erased on or from the optical disk, the switches 7, 8 are operated so as to turn ON. Thus, a current-voltage conversion load resistance of each preamplifier 21, 22 is divided into two lines shown by 3, 4; 5, 6 respectively, and the switches 7, 8 are provided in parallel with one of them, i.e., 4, 6, and the current-voltage conversion load resistance is changed by turning them off at the time of reproducing a signal, and turning them on at the time of recording and erasing the signal. Thus, the focus error signal comes not to be put into the disorder, and in addition, a variable gain circuit comes to be unnecessary.
SHIMADA TOSHIYUKI
KIKUCHI NOBORU
