This stereo graphic equaliser is very compact and quite cheap to build. However, it has the performance to match full-blown commercial models that are far more expensive. Plus, it can be used in a wide range of applications from AC or DC supplies. T his new graphic equaliser was prompted by a reader’s suggestion to revise an old 3-band parametric equaliser design. However, when we looked at updating the design we were conscious that parametric equalisers can be quite confusing to use – you never quite know how to vary the controls to obtain a desired effect. By comparison, graphic equalisers are much more intuitive – you can see which bands you are boosting or cutting and it is quite easy to repeat the settings after a particular listening or recording session. Used carefully, a graphic equaliser can make a considerable improvement to overall sound quality.
It is able to smooth out the frequency response of the reproduced sound, cure peaks, dips or lumps in a loudspeaker’s response, or simply and subtly change the program’s tonal quality to your liking. This 10-octave unit uses an individual slider potentiometer for each octave, giving you far more detailed control than is possible with simple bass and treble controls. And of course, the settings of the slider potentiometers provide a visual graph of the equaliser adjustments with the centre position providing a flat response in the respective octave – ie, no cut or boost. A slider adjusted above centre shows the level of boost and a slider below centre shows the level of cut. This is why it is called a ‘graphic’ equaliser.
Source : Everyday Practical Electronics