This is a schematic diagram of an electrical harmonic graphic equalizer. You can specify the number of channels as required. All you need to do is connect the following components in parallel: C1, C2, R1, an ohm amplifier, potentiometer, and a 470 ohm resistor. The boost frequency is determined by C1, C2 and R1. See the C1, C2, and R1 combination versus frequency graph.
For op amp you can use op amp IC TRX6221, NE5532 or LM833. Use a regulated power supply and high-quality components for high-quality audio output.