| 摘要 |
PURPOSE:To change the frequency characteristic of an amplifier in accordance with a speaker by removing the part of a feed-back signal to an amplifier after a speaker change-over switch and returning it to the feed-back input terminal of an amplifier. CONSTITUTION:The signal inputted to the terminal 1 of an IC1 for the amplifier is amplified by the IC1, outputted to a terminal 5, guided through a direct current cut capacitor 10 to a speaker change-over switch 2. A feedback resistance 3 is always connected from the output terminal 5 of an IC1 to the feedback terminal of the IC1. Further, the part of the output is fed back from the terminal of the built-in speaker 5 through the series circuit of a capacitor 9 for the feedback and a resistance 8 to the terminal 2. Only when the switch 2 falls to a side A, the part is fed back through the capacitor 9 and the resistance 8. Thus, by the switch 2, the feedback loop can be changed, and consequently, the frequency characteristic of the IC1 can be changed by the built-in speaker 5 and an external speaker 7. |
