| 摘要 |
PURPOSE:To reduce back noise in television sound by decreasing a sound quality control voltage via a diode and a resistor in selecting the television mode by a reception mode switching control signal. CONSTITUTION:At the time of the video mode, a screen mode switching signal goes to a high level 'H', a diode 11a is turned off and a sound quality control voltage reaches a voltage set by a sound quality adjusting variable resistor 12. In the case of the television mode selected, the screen mode switching signal goes to a low level 'L' and a television mode display LED 13 is lighted. The diode 11a is turned on at the same time and a resistor 11b is inserted between a slider of the sound quality adjusting variable resistor 12 and ground, resulting that the sound quality control voltage is decreased and the sound quality is less than that at the video mode. Thus, the optimum sound quality adjusting range is obtained at both video mode and the television mode. |
