This is 12V stereo tone control circuit electronic. Take a note that you must connect the circuit before the amplifier module. The output of tone control must be connected to the input of the amplifier.
There are will be four potensiometers used for this tone control circuit: volume level, bass level, treble level and balance adjustment. For better result, use better components with small tolerance value for example metalfilm resistors, MKM capacitor etc.
This schematic diagram come from circuit: 12V Stereo Tone Control
Go to that page to read the explanation about above circuit design.
In the electrical sector, a schematic diagram is usually used to describe the design or model of equipment. Schematic diagrams are usually utilized for the maintenance and repair of electronic and electromechanical devices / units. Original schematics were made by hand, using standardized templates or pre-printed adhesive symbols, but nowadays Electrical CAD computer software is often used.
In electronic design automation, until the 1980s schematics were virtually the only formal representation for circuits. More lately, using the progress of computer system technology, other representations were introduced and specialized computer languages were developed, because with the explosive development of the complexity of electronic circuits, classic schematics are getting less practical. As an example, hardware description languages are indispensable for contemporary digital circuit design.