The first diagram shown below is perhaps the simplest of its kind. It uses just one transistor as the active part and a few other common passive tone control components.
T1 used is a low noise type general purpose audio transistor, along with tone optimization; T1 also provides a certain degree of pre-amplification to the applied audio input.
The circuit may be introduced in between an input audio source and the external power amplifier.
The pot at the bottom is the treble control, gives a cut of 15 dB at 100 Hz, while the upper control which the bass adjust knob, provides a boost of 15 dB at around 15 kHz.
The next tone control circuit uses an IC 741 as the main active part and provides comparatively better response than the previous circuit. The circuit configuration is basically a Baxandall type, which also includes bass and treble control facilities through the pots VR1 and VR2 respectively.
The above two circuits if combined together can produce some outstanding results as far as sound enhancement is concerned. The figure below shows how it’s done by connecting the inputs and outputs of the two circuits in series. The configuration provides you with four discrete controls enabling very sharp and intense sound frequency optimizations, however with the bass at full thrust may cause considerable heating of the amplifier devices.
The transistor circuit operates with a single power supply; the IC circuit will however require dual supplies. The voltages may be anywhere between 6 to 12 volts DC for all the above circuits. The configurations shown above are for a single channel, two identical sets may be used for enhancing both left and right tracks with stereo amplifiers.