Attenuated feedback tone circuit

It is an attenuation-feedback tone control circuit composed of transistors and RC networks. In the circuit, RPz is the bass
control potentiometer , and RP3 is the treble control potentiometer . When the sliding points of RPz and RP3 are both located at the left end, the bass is
attenuated once by R and ‰, and the treble is attenuated once by the negative feedback of the R5 branch. , while the midrange is
attenuated by R4, R6 and negative feedback at the same time, resulting in high and low bass enhancement.
    When the sliding point of RP2 gradually moves from left to right , the bass will be further attenuated by the gradually increasing impedance of the chopper
, and at the same time, the bass negative feedback will gradually take effect and increase step by step. When the sliding point of RPz moves to the right end, the bass
is attenuated to the maximum and the feedback reaches the deepest level, while the mid-range and high-pitched sound still maintain the original attenuation and feedback amounts, which
results in the maximum attenuation of the bass.
    When the sliding point of Wei and Wei gradually moves from left to right , the treble is attenuated by the gradually increasing resistance of RP3, and
at the same time it is subject to the gradually increasing negative feedback effect of the island branch. When RP3 is moved to the far right, the treble is attenuated the most,
and the negative feedback reaches the deepest level, which results in the maximum attenuation of the treble.
    Circuit characteristics: The control range when the bass is 30№ is ±20dB; the control range when the treble is 10kHz is ±15dBo .
This circuit has a large control range and small distortion, but the control characteristics are greatly affected by the VT2 amplification factor.