| 摘要 |
PURPOSE:To provide flat output frequency characteristics without reinforcing an unrequired band regardless of an output level in a low-frequency sound reinforcing circuit for changing low frequency characteristics corresponding to the output level. CONSTITUTION:The output level of a power amplifier 10 is detected by an output level detection circuit 13 and equivalent resistance R (Q11) between the collector and emitter of the transistor Q11 of a control circuit 2 is changed. The transistor Q11 changes a positive feedback amount in a secondary system active high-pass filter 1 for reinforcing low-frequency sound provided in the preceding stage of the power amplifier 10. The selection degree Q of the secondary system active high-pass filter 1 becomes small when the output level of the power amplifier 10 becomes large and becomes large when the output level becomes small and the flat output frequency characteristics are realized without reinforcing the band equal to or less than 20Hz. |
