| 摘要 |
PROBLEM TO BE SOLVED: To reduce the occurrence of shock sound to min. when a gain setting value is changed-over stepwise. SOLUTION: A variable gain control circuit is provided with a current valve switch part 2 for obtaining a pair of transient current I1 and I2 which are provided with a transient response waveform based on a control signal Vs and are changed by opposite polarities, a variable current source 3 for obtaining variable currents Im1 and Im2 respectively corresponding to the transient currents I1 and I2 and a current control type variable gm amplifier 4 by which a current gain is directly controlled by a gain control current Ic=Im1+Im2 which is obtained by adding the variable currents Im1 and Im2. When the gain control current Ic is changed-over into a current setting value corresponding to the gain, the current setting value in one of the first variable current source 31 or the second variable current source 32 where the variable current is zero is changed-over and, then, the variable currents Im1 and Im2 are transiently changed so that shock sound at the time of change-over is suppressed to min.
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