Equivalent circuit with bass attenuation

When RPl is adjusted to point A, C is short-circuited
(1) Only the effect of Vi on Vb is considered, and the effect of Vo on Vb is not considered. The equivalent circuit is shown in Figure 1-80 (a)
    . o RPi is adjusted to point C. '& is short-circuited
    (1) When only the effect of vj on Vb is considered and the effect of Vo on Vb is not considered, the equivalent circuit is shown in Figure 1.81 (a)
. The capacitive reactance to the low audio signal c5 is large, and the attenuation of Vi is large, so Vb is small; while the capacitive reactance to the high audio signal island
is small, and the attenuation of vi is small, so Vb is large. As a result, low-frequency audio signals are relatively attenuated.
    (2) When only considering the effect of vo on Vb and not considering the effect of Vi on,,b, the equivalent circuit is shown in Figure 1-81 (b)
. The capacitive impedance to the low audio signal island is large, the bypass effect is small, the negative feedback is strong, and Vb is much weakened. For high -frequency signals,
the capacitive impedance of the island is small, the negative feedback is weak, Vb is weakened less, and the low-frequency audio is relatively weakened. As a result, the low-frequency audio is attenuated
. Combining these two aspects, it can be seen that when RPi is at point C, the t bass audio is attenuated, and its Vo/vi curve is shown in
Figure 1-81 (c).