Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10KHz and 50Hz. As the controls are passive, the first transistor, Q1, is configured as common-collector to act as a buffer stage. The last transistor, Q2, provides a slight boost. Note that the gain of the output of the Baxendall circuit is less than one because of passive nature of it. The output is designed to feed an amplifier with input impedance of 10kohms to 250kohms.