| 摘要 |
PROBLEM TO BE SOLVED: To prevent a load drive circuit from burning at the time of short- circuiting an output circuit by providing a protective means for suppressing the current flowing through a power amplifier circuit when a current detecting means is detected that the current flowing through the ground circuit of a preamplifier circuit is not less than a prescribed value. SOLUTION: When a current detecting part 32 detects the current not less than the prescribed value, a mute signal is outputted to the (+) side of the output signal of a preamplifier 31. A mute circuit is composed of a transistor Tr1, for example, the signal (+) side is grounded by the mute signal and the output signal to a power amplifier part is cut off. As a result, the output of the power amplifier part is stopped and a ground pattern (ground circuit) inside a head unit part 3 is protected. Besides, when there is no abnormality such as grounding and the current value is returned to the normal level, the current detecting part 32 stops the operation of the mute circuit and the power amplifier part can automatically be recovered to normal operation.
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