Loudness Control

Specification
Power 12 Volts nominal 5mA current drain
Gain 13dB @ 20Hz, 9dB @ 20kHz
Input Impedance 27Kohm @ 1Khz

Notes
This circuit uses a three stage, passive, RC filter to tailor the frequency response, followed by an op-amp in non-inverting mode to provide the gain. The frequency response is shown below:
Frequency Response