Graphic Equalizer Circuit for 10 Frequency Bands

The circuit was designed to create ten different frequency bands to be handled by a single graphic equalizer to produce and maintain a predetermined area of frequencies.

• Graphic Equalizer – a common type of equalizer considered as a high-fidelity audio control which consists of a bank of sliders for cutting and boosting different frequency ranges or bands of sound and allows the user to see graphically and control individually a number of different frequency bands in a stereophonic system
• TL074 – low noise JFET quad operational amplifier with features such as high slew rate, latch up free operation, compensated internal frequency, low harmonic distortion, protection from output short circuit, JFET input stage with high input impedance, low offset current and input bias, low noise, and wide common-mode and differential voltage range

A graphic equalizer is one of the two kinds of equalizers commonly found in radio productions which derive its name from the rough graph of a sound’s altered frequency response that is formed by the slider control settings on the front faceplate of equalizer. A typical graphic equalizer consists of several audio filters/amplifiers with a specific audio range frequency.

In this type of circuit, ten ICs were used with their corresponding potentiometer for the regulation of frequencies. Each connection has common components and would only differ in the capacitor values that comprise each filter. This configuration forms a 10-band octave equalizer that will operate on the center frequencies with the adjustment on both ends. The filter will not intervene if the potentiometers RV1 to RV10 have been regulated in the middle for the passing signal. At this stage, the gain is one.

The slide potentiometers control the volume or gain in most graphic equalizers which is adjusted by moving a control button up or down. Proportionally, the upward sliding increases the gain and the placement of sliding potentiometers for each channel is side-by-side. The highest frequency adjustment is at the right while the lowest frequency at the left. Doing this arrangement allows the buttons to be patterned in a graphical way while representing the gain as a function of frequency for each channel.

The unit will act as a filter when the sliding is done on the output side where it cuts off the area while degrading the signal of the predetermined area of frequencies. On the other hand, if the sliding is done on the input side, the unit acts as a filter for passing the signal while being amplified for the predetermined range of frequency. The circuit is connected between the preamplifier and final power amplifier and the components used in constructing this circuit are of good quality especially for the potentiometers and capacitors.

The use of graphic equalizers may be found in consumer products that are commonly in middle- and high-end stereophonic sound systems. The programs for graphic equalizers are available for use in a personal computer for fine tuning of sound. They are also found as standard practice in all professional recording studios, live sound reinforcement systems, and some high fidelity systems where a graphic equalizer uses a spectrum analyzer to compensate for the room acoustics and room frequency response, with matching frequency bands. This is very essential due to the standing waves produced by the size of the room and the materials in it which causes some sound frequencies to be louder than the others. All the graphic equalizers function by dividing the frequency response range into separate frequency bands even if they come in different designs.

Source:users.otenet.gr/~athsam/EQ_10_band.htm