Five-Band Stereo Graphic Equalizer

FIVE-BAND STEREO GRAPHIC EQUALIZER This design of a stereo equalizer is fairly unusual because it is based on induc- tive feedback. In theory, the feedback circuit around opamp Ai would provide 15 dB amplification or attenuation of each frequency range, but in practice only about 13 dB is attainable owing to losses in the inductors. A virtually flat frequency response is obtained when all five potentiometers Pi to Ps are set to the centre position (0 dB). Total control range of the unit is about 33 dB. The TL072 dual opamp in each channel is a trade-off between cost and perform- ance in respect of noise and distortion. Set to 0 dB gain, a prototype of the equalizer produced 0.04% distortion at an input signal of 1 kHz; 1 V, and 0.13% at 5 and 10 kHz. Distortion is highest when the test frequency lies within one band that is fully attenuated while the other four are set to maximum gain. In this condition, test measurements resulted in a maximum distortion of 1.5%, which is certainl...