Equivalent circuit when treble is attenuated

Treble attenuation
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(1) When only considering the effect of Vi on Vb and not considering the effect of vo on Vb, the equivalent circuit is shown in Figure 1-83 (a)
. Because RP2 is larger, the attenuation of Vi is larger, and the impact on high and low audio frequencies is not obvious.
    (2) Only consider the effect of vo on Vb, without considering
the effect of vl on Vb, the equivalent circuit is shown in Figure 1-83(b) o'
Because R13 is small and base) 2 is large, the negative feedback effect It is obvious
that since the capacitive reactance of Q to high audio frequency is small and the capacitive reactance to low audio frequency
is large, the negative feedback to the high audio frequency signal is strong, which will relatively weaken the high audio frequency. Based on the above situation, when
Q is at point F , the characteristic curve
of high audio frequency being attenuated oVo/Vi is shown in Figure 1. 83(C)o