In professional audio engineering, it is common practice to implement not only the inputs and outputs as differential stages, but also to design the entire signal processing chain accordingly. High-quality ADCs frequently offer differential inputs, while advanced DACs often provide differential outputs. Leading semiconductor manufacturers specializing in audio electronics supply fully differential operational amplifiers, which enable the realization of suitable filters. This article introduces four PCBs designed for such applications, which can naturally be combined as needed.

Differential op-amps were already covered in the three-part article series “Analogue Filter Design,” published in Elektor between September 2020 and January 2021. In Elektor 11-12/2022, I presented suitable filter software. An article in Elektor May/June 2023 dealt with single-ended examples of active filters (such as active 1-kHz low-pass and band-pass filters).

For the differential version presented he...