The thermionic valve and its uses for low powered guitar amplification

In accordance with modern day demands for reduced sound pressure levels in recording and live performance situations, this thesis describes researched methods for accurately reproducing the full power ‘valve sound’ at low power. The output harmonic weighting of the valve sound is examined via an array of plots depicting individual harmonic amplitude throughout the dynamic range of an ECC83 dual triode. Comparative subjective analysis of a referenced high-voltage solid-state preamplifier, with acclaims of large signal capabilities comparable to a valve amplifier, and the ECC83 topology, demonstrates that the weighting of high order harmonics is not only audible but can ultimately determine preference of certain distortion characteristics. Using a reduction in triode anode voltage in parallel with careful management of input signal amplitude, a harmonically accurate reproduction of the ‘valve sound’ is achieved at a power reduction factor of 9.796. Dynamic data of the ECC83s overload region is collated and included in the thesis as a reference for future digital dynamic modelling. The use of ECC83 triodes at anode voltages below 110VDC is shown to have perceivable detrimental effect upon output harmonic content and consequently for accurate production of the valve sound below this threshold the thesis concludes that valve modelling is required.