This is a 3-Way Tone Control circuit. It can be used in any audio system and it is able to boost or attenuate the audio spectral content at low, mid and high frequencies in the range of -16 to +16db. It is based on the popular low – noise NE5532 operational amplifier. The electronic circuit has three separate adjustable filters. The first one is an adjustable-gain low pass filter; the second one is a band –pass adjustable filter and the third one is an adjustable high-pass filter for bass, mid and high frequencies, respectively. The cut- off frequencies for the bass and high frequency filters are about 200 Hz and 2 KHz, respectively. The central frequency of the band-pass filter is about 1 KHZ.
The normal gain (when pots are at midrange) is fixed to 0db but it can be easily modified by adjusting R2. The normal gain (G) is given by G=20*LOG (R2/R1). The cut-off and central frequencies of the filters can be also easily modified by replacing C5, C6, C7 and C8 with appropriate values. If you choose to build this circuit twice for a stereo system, take care to use low tolerance components to ensure same response for both (R and L) channels. We must also say that there is some varying dc-offset at the output. This is not a problem if there is any ac-coupling capacitor in the next audio stage (following the tone control circuit) but if you face any problems due to this offset you must add an ac-coupling capacitor by yourself.
Artwork by: A.G
3-Way Tone Control Circuit / PCB details