| 摘要 |
PROBLEM TO BE SOLVED: To enable only one signal route to deal with input audio signals at different signal levels by operating an operational amplifier as a buffer circuit when an operating switch is in a large signal input mode and operating the operational amplifier as an amplifier circuit when the operating switch is in a small signal input mode. SOLUTION: When inputting the audio signal of low signal level from a microphone to an audio input terminal 1, a slide switch 6 is set at a position so as to short-circuit contacts 6b and 6a. As a result, since a first switching transistor 5 is turned on, an operational amplifier 2 is operated as a non-inverted amplifier circuit. When the audio signal of high signal level is inputted to the audio input terminal 1, since a second switching transistor 9 is turned on and the first switching transistor 5 is turned off, the operational amplifier 2 is operated as a buffer circuit.
|
