Home > Circuits > Parametric Equaliser
Modified:21:23, 22 October 2013
A Parametric Equaliser that allows you to cut or boost any frequency from 100Hz up to 8KHz.
Ideal for removing feedback (notch filter), improving sound quality of audio or for tailoring your own sound effects.

I must admit this is a wicked circuit considering its simplicity. I have simulated the circuit on software and its performance was very impressive, but have yet to build it.

It is basically an audio filter that can cut and boost signals at any frequency from 100Hz to 8KHz. Its application for improving/altering sound are wide.

The EQ has two main controls, the gain of the filter (VR1) and the frequency at which it is centred on being a dual-potentiometer VR2. With VR1 at centre position, the gain is 1. At minimum position the gain is 0.2 and at maximum about 6.

The bandwidth of the filter varies a little but has a surprisingly high Q factor (range of frequency from the centred one that is affected).


The frequency range of the filter can be seen in the graph being 100Hz to 8KHz. It will make operation much easier to use a Logarithmic potentiometer as the response shows.

A resistance from 500K down to 100K only covers 120Hz and below 100K the frequency quickly rises to 8KHz . Dual log pots are a bit pricey but its well worth the spend. Fixed resistors can be put in place of VR2 and even values switched in and out if you only want to affect one or two frequencies rather than using a dual potentiometer.

Signal at maximum boost

Test signal input:

220Hz @ 2volts p-p

Signal at maximum cut

Circuit simulation - might need to save as file first.

Designed and Written by Phil Townshend 2007
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