This tone control circuit use very popular Baxandall configuration, a simple circuit configuration that provides boost and cut control in continuous manner. This circuit is very cheap to build, and it’s commonly implemented in commercial product. Here is the circuit’s schematic diagram:
The transistors can be substituted by any general audio transistors with small current gain more than 100 (BC547, 2N3904, and many more). The supply voltage for this circuit is 9-15V DC.