New active RC bode-type variable equaliser

A new variable equaliser is proposed, based on Bode´s classical variable equaliser transfer function. The advantages of the new circuit are that it uses a single variable resistor to produce the required range of variation, it contains only a single operational amplifier; and, since the output terminal of the circuit coincides with the output terminal of the amplifier, the circuit is suitable for direct cascade connection without buffer amplifiers. Application of the inverse active transformation to the proposed circuit leads to another new variable equaliser circuit. Laboratory models of both networks have been built which realise a `fan¿ and a `bump¿ equaliser with a variable loss of ± 10 dB; the measured responses are shown to be in good agreement with those obtained by computer simulation, assuming ideal amplifiers.