3 Band Graphic Equalizer Circuit

The circuit illustrates the use of 3 frequencies to produce a graphic equalizer that will be used for acoustic signals.

• Equalizer – a passive or an active electronic element or circuits (like tone control) used for the reason of altering or flattening the frequency response characteristics of a system
• TL072 – a low noise JFET input operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at the JFET input stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumption
• NE5532 – an internally compensated low noise dual operational amplifier with features such as full power bandwidth up to 140 KHz, input noise voltage of 8 nV, common mode rejection ratio, 9 V/us slew rate, high DC voltage gain, 32 V peak to peak voltage swing, wide supply voltage range from 3 V to 12 V, unity gain bandwidth at 10 MHz, and internal frequency compensation

One of the two kinds of equalizers is the graphic equalizer which originates its name from the rough graph of an audio’s altered frequency response which is formed by the glider settings on the front faceplate of an equalizer. The circuit pertains to a classic design by which it can regulate the tone of the acoustic signals into three different ways which includes the low, mid, and high frequencies. This is made possible by utilizing a tone control of the 3 frequencies. A graphic equalizer typically consists of several audio filters or amplifiers with a specific audio range frequency. With the slope range of 18 dB/oct, the amplification or boosting and attenuation or cutting of signals can be done.

The circuit is being supplied with 15 V, but can also be supplied by a 9 V up to 30 V power source. The 0 V should be connected to the pin 4 of IC1, which will give half of the supply in the non inverting input of the IC1. Simultaneously, the pins 3 and 5 are similar which will not be connected to the ground. The tones of frequencies are being adjusted by the 100K Ohms linear potentiometer RV1 for low frequencies, RV2 for mid frequencies, and RV3 for high frequencies.

Graphic equalizers are widely seen commonly in middle and high end stereo sound systems and other consumer products. They are used to correct the reduced level of high frequencies in early telephone systems as well as in modern digital telephone systems and in individual channels of a mixing board, where the sound waveform is being applied with equalization. They are available for use fine tuning of sound in personal computers. But most importantly, they are used as a standard practice in live sound reinforcement systems, professional recording studios, and some high fidelity systems where a spectrum analyzer is being used by a graphic equalizer to compensate for the room frequency response and room acoustics. Although graphic equalizers come in different designs, the all function by dividing the frequency response range into separate bands.