Taming the Red Llama—Modeling a CMOS-Based Overdrive Circuit

Lasse Köper; Martin Holters
DAFx-2020 - Vienna (virtual)
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.