| 摘要 |
PROBLEM TO BE SOLVED: To compensate deterioration of reproduced sound pressure caused in the vicinity of a lowest resonance frequency of a loudspeaker, and to achieve heavy low-pitched sound reproduction of the loudspeaker, by making improvement on a constant and structure of a DC feedback circuit for removal of an output offset voltage used in a constant voltage amplifier. SOLUTION: An inverse integrated type DC feedback circuit (3) is combined with a differential amplifier designed to have a considerably large raw gain in a low frequency region. A characteristic as an inductive load becomes conspicuous because a mechanical impedance rises in the vicinity of the lowest resonance frequency of the loudspeaker, and as a result, an output of the differential amplifier has a delayed voltage phase. Since the inverse integrated type DC feedback circuit (3) has a voltage phase advanced by about 90°with more than a cut-off frequency, positive feedback can be made by setting the cut-off frequency in the vicinity of the lowest resonance frequency of the loudspeaker. Operation of the amplifier in the vicinity of the lowest resonance frequency is made similar to that of a constant current amplifier by setting a DC feedback amount to an appropriate value, whereby deterioration of reproduced sound pressure is compensated. COPYRIGHT: (C)2008,JPO&INPIT
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