| 摘要 |
PURPOSE:To improve both the acoustic and tone control characteristics, by fixing the output of the 3rd amplifier at a certain level of potential in the case of a tone flat and accordingly actuating the 1st amplifier as just an ordinary amplifier to reduce the effect of a tone circuit element. CONSTITUTION:The sliders of variable resistors VR11 and VR12 are set at their centers respectively to obtain a tone flat. Thus these sliders are connected to an earth. The output impedance is sufficiently low for the 1st and 2nd amplifiers 13a and 13b since the negative feedback is applied to these amplifiers. On the other hand, the values of resistances R13-R16 and variable resistors VR11 and VR12 are larger than the above-mentioned output impedance by several digits, and these elements can be ignored. At the same time, the input terminal of the 3rd amplifier 13c is grounded through resistances R17 and R18 plus a capacitor C12, and the output impedance is sufficiently low compared with a resistance R10 due to the negative feedback. Then the potential of the output terminal of the amplifier 13c is fixed virtually at the earth potential. |
