Despite the recent trend of digital transformation in the music industry, the popularity of Guitar-Effect-Pedal (GEP) designed with analog components has never declined. This paper describes the complexity of the nonlinear characteristics of analog circuitry in a GEP, which originates from not only clipping diodes but also the OPA itself. It is well known that starving of the supply voltage influences its sound. Based on this fact, we designed a bias circuit to control various distorted transfer functions. Particular attention is paid to the difference in the generation mechanism between the odd and even distortion of intermodulation associated with the hysteresis change. Those transfer functions were analyzed in detail, using each 9th-order polynomial approximation as a reference.
Authors: Masaki Inui (Hiroshima Institute of Technology), Toshihiko Hamasaki (Hiroshima Institute of Technology) and Menno van der Veen (Ir. bureau Vanderveen)