| 摘要 |
PURPOSE:To prevent misconnection of a positive feedback circuit, by providing an oscillation preventing circuit with the positive feedback circuit obtained from the reverse phase input terminal of a load for a power amplifier of a negative feedback constitution. CONSTITUTION:A speaker 14 is connected to a positive phase output terminal and a negative phase output terminal P of a power amplifier 11 of negative feedback constitution via cords 131, 132. Positive feedback is given to an input terminal of an amplifier via a feedback cord 15 from a reverse phase output of the speaker 14 to avoid the adverse effect of distorted voltage produced across the input terminals of the speaker 14. This positive feedback circuit is provided with a switch driving circuit 172 and an FET having holding function and an oscillation detecting circuit 171 having a level discriminating function, allowing to prevent that the circuit is in oscillation state through the misconnection of the feedback cord 15 to the positive phase input terminal Q of the speaker 14. |
