The present invention provides a vacuum tube audio amplifier which includes an audio pre-amplifying portion and an audio output transforming portion. The audio pre-amplifying portion includes an equalizer for enhanced sound quality and amplifies an audio signal, which is subsequently transmitted to the audio output transforming portion. Furthermore, the audio output transforming portion includes an audio output transformer which includes a plurality of stacked E-shaped silicon steel sheets and a plurality of stacked I-shaped silicon steel sheets, wherein the stacked E-shaped silicon steel sheets and the stacked I-shaped silicon steel sheets have a same height which is smaller than or equal to 48 mm.

Systems and methods that cancel distortion in the amplified outputs of a node by equalizing the distortion characteristics amplifiers in the node, so as to improve the effectiveness of predistortion applied to a downstream signal amplified by the node.

A power amplifier includes a class-D amplifier and an input signal supplier. The class-D amplifier includes an input portion and a switching device. The switching device is switched according to an input signal that is input to the input portion so that a current is supplied to a load from a power source via the switching device. The input signal supplier supplies the input signal to the input portion of the class-D amplifier, calculates a virtual output voltage to be output from a virtual power source having a prescribed internal impedance characteristic when a current to flow through the load is output from the virtual power source, and adjust an amplitude of the input signal according to the virtual output voltage.

An amplifier includes an amplification section for amplifying a musical tone signal input from an electric musical instrument. A plurality of speakers are connected to the amplifier. The amplifier includes a selection section selecting a speaker for outputting the musical tone signal amplified by the amplification section, among the plurality of speakers, a storage section storing a characteristic adjustment value which is a value for adjusting an output impedance characteristic or an input impedance characteristic of the amplifier according to a characteristic of the speaker for each of the plurality of speakers, an acquisition section acquiring the characteristic adjustment value corresponding to the speaker selected by the selection section from the characteristic adjustment values stored in the storage section; and a characteristic adjustment section adjusting the output impedance characteristic or the input impedance characteristic based on the characteristic adjustment value acquired by the acquisition section.