Here is the circuit diagram of a simple 3 band graphic equalizer circuit using a single IC and few components. The IC used here is LF 351 which is a wide bandwidth single JFET operational amplifier. The high input impedance of the IC makes this circuit compatible with most of the audio signal sources. The opamp is wired as an inverting amplifier. The input signal is fed to the inverting input of the opamp via the filter network. The filter network can produce a +/- 20 dB enhancement or cut on the three frequency bands 50Hz,1KHz and 10KHz.POTs R1, R2 and R3 can be used for adjusting the gain of the different bands.
Circuit diagram with Parts list.
- Assemble the circuit on a general purpose PCB.
- The Circuit can be powered from anything between 6 to 30V DC.
- I am using 12V here.
- Increasing supply voltage will of course increase the gain.
- The IC must be mounted on a holder.
- The electrolytic capacitors must be rated higher than the supply voltage.