Precision harmonics simulation for vacuum-tube electric-guitar pedals and preamplifiers
Kanako Takemoto, Shiori Oshimo, Toshihiko Hamasaki · The Journal of the Acoustical Society of America · 2016
Recently, vacuum-tube pedals have attracted many electric guitar players, though solid-state circuits or even digital processors are widely accepted. The purpose of this study is to clarify the origin of distorted timbre of the vacuum-tube pedal by circuit simulation with a novel vacuum-tube model. In general, the specific sound of vacuum tube for both hi-fi and electric guitar amplifier is attributed to the even number of harmonics originated from the inherent non-linearity. However, significant difference exists in the input signal amplitude between hi-fi and electric guitar system. The simulation with a conventional non-linear model has been limited within the regulated signal swing of hi-fi audio system. The dynamic non-linear phenomena for large signal, such as an input signal modulation, are not considered. Thus, unrealistic harmonics appear in the pedal simulation due to discontinuity of model parameters. The new model is obtained by physical analysis based on enough measurements, considering the actual input condition of pedal and preamplifier as well. The key property is a seamless modulation of non-linearity influenced by circuit operation. As a result, we have succeeded in simulating changes of the dynamic harmonics accurately for the first time.