| 摘要 |
PURPOSE:To prevent a howling phenomenon by allowing sound volumes of only low band portions to be reduced automatically when a voice output is detected and its output has increased enough to cause the howling phenomenon. CONSTITUTION:Output detection circuits 2 rectifies and synthesizes added voice outputs by a capacity 2-8 through diodes 2-9 and 2-10 and then voltage divides by resistors 2-4 and 2-5 and also are added to bases of a transistor 2-7 through a restricted series resistor 2-3. Once the voice outputs reach a level causing the howling phenomena, the transistor 2-7 turns ON and the transistor 3-1 turns OFF and the result is that in addition to a tone control circuit 1, the resistor 3-2 has been inserted. In such a case, a low band adjusting part balanced so far by the resistors 1-2 and 1-3 and variable resistor 1-4 and capacitances 1-6 and 1-7, by the insertion of the resistor 3-2 to the resistor 1-3 which determines the cut volumes for reducing, deteriorates the balance in a direction of attenuating, resulting in overall frequency characteristics have a low band cut type. |
