Tone control allows listeners to adjust sound to their liking. It also enables them to compensate for recording deficiencies, hearing impairments, room acoustics or shortcomings with playback equipment.
Below, we present the electronic schematic of a simple stereo tone control circuit. The electronic schematic is based on a design found on LM833N’s (op-amp) datasheet.
This circuit is a 2-way tone control. In other words, it is able to attenuate or boost bass and treble (2-frequency bands). The adjusting elements for bass and treble are the R1 and R2 stereo potentiometers, respectively.
The circuit has one low pass and one high pass filter at each audio channel. Both filters are almost flat-top at their pass-band. The flat-top gain of any filter can be varied between -20 and +20db, independently from the other one. The cut-off frequencies (-3db points) for the low and the high pass filter are preset at 340Hz and at 10 KHz, respectively. If you wish to alter them, refer to the design formulas at page 11 of the LM833-N’s datasheet.
The electronic schematic is quite simple and the circuit can be easily built on a universal board. However, you must take care to use low tolerance components to ensure the same response for both (R and L) audio channels. The circuit operates normally when connected to a low-impedance voltage source; otherwise a voltage-follower must be used at the input. Due to DC-coupling, any DC present at any input could cause some problems. So, use AC-coupling capacitors, if necessary.