For the op-amp, you can use op-amp IC TRX6221, NE5532 or LM833. Use regulated power supply and high quality components to obtain the quality audio output.

This is the design diagram of 5 band graphic equaliser circuit build using operational amplifier chips, the NE5532 or LM833. The op-amp ICs is a good choice because of inexpensive and comes with fairly good quality output. Each IC contains dual op-amps circuit, so you will need 4 ICs of NE5532 or LM833 to build this 5 band graphic equaliser.

For maximum audio performance, use:

• Regulated power supply circuit (use LM78xx)
• Use MKM type of nonpolar capacitor
• Use tantalum type of bipolar capacitor (electrolytic capacitor)
• Use metalfilm type of resistor

Equaliser circuits generally divide the audio spectrum into separate frequency bands and have independent
gain control for each band. The output of each band is mixed at IC4(A) and then fed to an audio power amplifier. Proper quality factor (Q) needs to be selected to avoid overlap in adjacent bands as this introduces colouration into the audio signal.

The potensiometers (VR1 through VR5) are in the signal path and hence should be of the best quality possible. Wrap the body of the pots with bare copper wire and solder the other end of the wire to ground. Since the filters are very sensitive and for maximum performance, all resistors should be metal-film type and the capacitors should be polyester type.

5 Band Graphic Equaliser Document Reference:

More explanation about how the circuit work, download this document:

5 Band Graphic Equaliser Project

1 file(s) 191.71 KB

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Download datasheet document:

LM833N PDF Datasheet

1 file(s) 1.85 MB

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NE5532 PDF Datasheet

1 file(s) 960.82 KB

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This circuit operated with 12VDC symmetrical / dual polarity power supply. Power supply circuit provided on above diagram. For better power supply output and of course will improve the audio performance, you may use IC regulator LM7812 and LM7815.

The equalizer uses four pieces of variable resistor to cut and boost four range of audio frequency, that are:

• Low frequency: Freq. 35-680Hz
• Medium frequency: Freq. 150-3kHz
• Medium/semi high frequency: Freq. 450-8.5kHz
• High audio frequency: Freq. 750-15kHz

Download 4 Band Equalizer circuit in PDF document from below link:

4 Band Equalizer Circuit

1 file(s) 14.60 KB

Download Circuit Diagram

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.

Here the 20 band graphic equalizer schematic diagram. This is stereo graphic equalizer, it should be 2×10 channel equalizer. Graphic equalizers device are popular with both domestic users and professional users. This equalizer is has simple design and easy to construct. It has no coil. It uses 15V split / dual polarity power supply to work (+15V / 0? / -15V). You may use search menu to find the circuit diagram of split / dual polarity / symmetrical power supply.

Equalizer allows the listener to correct deficiencies in the linearity of either his speaker system alone, or the combination of his speaker system and his living room.

20 Band Graphic Equalizer PCB design layout:

You can download the full explanation about how it’s work and also the detailed PCB layout and how to construct/assemble this equalizer circuit. Please download the document from the following link:

20 Band Equalizer Graphic Equaliser

1 file(s) 2.89 MB

Download Circuit Manual

Good luck..