The Baxandall Tone Control Circuit

The circuit discussed here is an example of the Baxandall tone control circuit, illustrated in Fig. 0.0.2, which is an analogue circuit providing independent control of bass and treble frequencies; both bass and treble can be boosted or cut and with both controls at their mid positions, provides a relatively flat frequency response, as illustrated by the blue ‘Level response’ graph line in Fig. 0.0.3. The original design, proposed by P. J. Baxandall in 1952, used a valve (tube) amplifier and feedback as part of the circuit to reduce the considerable attenuation (about −20dB) introduced by the passive network, and to provide true bass and treble boost. There are still many variants of the circuit in use, both as active circuits (with amplification as originally proposed), and as passive networks without an incorporated amplifier. In passive variants of the Baxandall circuit, extra stages of amplification may be used to make up for the approximately −20bB attenuation caused by the circuit.

Read the original 1952 paper "Negative-Feedback Tone Control" by P. J. Baxandall B.Sc.(Eng.) published in "Wireless World" (Now Electronics World)