Correcting Transducer Response with an Inverse Resonance Filter

Steven van Raalte set out to combat the resonance in phono cartridges. Manufacturers often rely on this resonance to compensate for the hf roll off caused by cartridge induction and load impedance. Although the frequency response can be made to look quite flat, the result is often severe phase shifts and resultant time smearing. Steven develops a Sallen-Key based topology that undoes' the time smearing, and shows how it makes the square wave response of the combination cartridge- filter impeccable. He even shows how to dimension the filter such that the RIAA 2120 Hz turnover point can be deleted and become part of the filter! At the end of the article he also shows how to use the technique to compensate for the resonance at the low frequency side of a speaker.