| 摘要 |
PURPOSE:To reduce gang errors while eliminating a sliding noise and a thermal noise by adjusting a signal level by dividing the voltage of an input signal through capacitors including a variable capacitor in a volume controller etc. CONSTITUTION:Variable capacitors (C) 1 and 2 are connected in series and applied with an input signal Vin, and a signal at an intermediate point A is obtained through a buffer amplifier 1 having an extremely high bias resistance R1; and either or both of the C1 and C2 are varied to vary the output Vout of the amplifier 1. To make the low cut-off frequency of this circuit constant, an inverting amplifier 2 is used and its output is fed back negatively through the C4 and R2. Further, variable C5 and C6 are connected into multistage constitution to obtain a wide variable range, and this is usable as an audio attenuator. |
