Equal loudness control circuit

Figure 1-87 is a better equal loudness volume control circuit . It only uses an ordinary potentiometer and uses
few components, but the effect is quite significant. The working principle of this circuit
is: when the internal impedance of the signal source is much smaller than Rc, the load impedance is larger than Rp, and Rp is much larger than I and Rz, the value of the capacitor C only affects the high and medium audio frequencies. , it can be regarded as an open circuit for low audio frequency