A twin-t amplifier with stable gain and variable selectivity

The principles of operation of low-frequency ¿twin-T¿ selective amplifiers are discussed and information is given regarding the design of such amplifiers in order to obtain a stable and predictable performance. The paper opens with the analysis of a simple system and its shortcomings. The twin-T network and the operation of its associated amplifier are then considered in detail. The complete system is analysed and design parameters are given for optimum performance. Details are given of the construction and performance of both valve and transistor amplifiers which were designed according to the principles outlined.