A highly versatile second-order active-filter building block for low-Q applications (Q≤125) is described. The versatility is obtained by combining features inherent in the Sallen-Key circuit topology and those pertaining to hybrid-integrated circuits (HIC's). A high degree of circuit stability is obtained by designing individual network functions to depend primarily on the characteristics of stable thin-film resistors and capacitors. Frequency- and Q-sensitivity are examined in detail. Methods of minimizing Q-variation with respect to the active and passive elements are discussed. Lower bounds on the Q-variation obtainable with the hybrid-integrated filter building blocks are given. All possible second-order network functions, including the all-pass function, can be obtained with the building block. The resulting universality and standardization permit the complete design of active filters consisting of cascaded building blocks by computer.