Unlike the 10-band graphic equalizer in our previous circuit that use a gyrator circuit, this 3-band graphic equalizer circuit uses Baxandall topology, similar with the Baxandall tone control but with additional mid frequency control. The figure below shows the schematic diagram of the circuit.
The operational amplifier employ an LF351 IC chip, but any low noise op-amp will be suitable for this equalizer application. Unlike in the application of 10 channel equalizer, the passive components in this 3-bands graphic equalizer circuit are not critical since this circuit doesn’t need a critical frequency band separation. Resistors with 5% tolerance are more than enough, and ceramic capacitors with 10% tolerance will be adequate. Off course you can use better component but the performance improvement won’t be noticeable. This circuit need only a single supply, so this would be great for car audio or simple home audio application. [Circuit's schematic diagram source: circuitstoday.com]