The following diagram is the circuit diagram of 20 band stereo graphic equaliser which will controlling the audio signal in specific frequency range.
The power supply used for this circuit is symmetrical (dual polarity) type, 15V DC.
This circuit must be connected before the amplifier circuit. For maximum performance, you may use high quality electronic component such as metalfilm resistor, MKM capacitor (nonpolar), tantalum capacitor (bipolar). You may replace the power supply module with regulated and stabilized power supply or just add IC LM7815 after R35 and IC LM7915 after R36. With good components and good power supply, then the sound quality will get better. This circuit uses 6x IC TRX6221, if you can’t find this IC at your area then you may try NE5532 or LM833 operational amplifier IC.