This circuit can be added to any audio amplifier design, consisting of a good tone control with an operational amplifier. The operational amplifier may be the 741 or equivalent and the power supply is symmetrical or dual. The circuit is placed between the signal source and the amplifier input. The pots used should be linear. Note that the input cables and output signals must be shielded. For a stereo version must be mounted two identical units, one for each channel. As consumption is very low, the power can be obtained from own amplifier with which the control will work. Anyway, it is very important to add a good filter to prevent any noise. For the stereo version, double operationals such as the LM1448 or LM1548 may be used.