The Red Llama guitar overdrive effect pedal differs from most
other overdrive effects because it utilizes CMOS inverters, formed
by two metal-oxide-semiconductor field-effect transistors (MOSFETs), instead of a combination of operational amplifiers and
diodes to obtain nonlinear distortion. This makes it an interesting
subject for virtual analog modeling, obviously requiring a suitable
model for the CMOS inverters. Therefore, in this paper, we extend
a well-known model for MOSFETs by a straight-forward heuristic
approach to achieve a good match between the model and measurement data obtained for the individual MOSFETs. This allows a
faithful digital simulation of the Red Llama.