An amplifier (100, 200) comprising: an input (105, 205) configured to receive a signal from a musical instrument; an overdrive shaping circuit electrically coupled to the input (105, 205) and configured to receive the input signal, the overdrive shaping circuit including a soft clipping cell with diodes (D4, D5, D6, D7) arranged in a current-steering bridge with a fixed resistive load configured to have a peak clipping voltage level, and a sag controller configured to produce, in response to the audio signal input to the clipping cell reaching a defined overdrive level, a controllable amount of sag for the clipping voltage level of the soft clipping cell with a time constant that corresponds to typical musical performance tempos; wherein the amplifier (100, 200) further comprises: a power amplifier circuit electrically coupled to the overdrive shaping circuit, the power amplifier circuit configured to receive a harmonic shaped signal from the overdrive shaping circuit, wherein the power amplifier circuit includes a switchmode amplifier configured to amplify the harmonic shaped signal, and means to increase the output impedance of the switchmode amplifier; and an output coupled to the power amplifier circuit, the output configured to output a signal amplified by the switchmode amplifier. an input (105, 205) configured to receive a signal from a musical instrument; an overdrive shaping circuit electrically coupled to the input (105, 205) and configured to receive the input signal, the overdrive shaping circuit including a soft clipping cell with diodes (D4, D5, D6, D7) arranged in a current-steering bridge with a fixed resistive load configured to have a peak clipping voltage level, and a sag controller configured to produce, in response to the audio signal input to the clipping cell reaching a defined overdrive level, a controllable amount of sag for the clipping voltage level of the soft clipping cell with a time constant that corresponds to typical musical performance tempos; a soft clipping cell with diodes (D4, D5, D6, D7) arranged in a current-steering bridge with a fixed resistive load configured to have a peak clipping voltage level, and a sag controller configured to produce, in response to the audio signal input to the clipping cell reaching a defined overdrive level, a controllable amount of sag for the clipping voltage level of the soft clipping cell with a time constant that corresponds to typical musical performance tempos; wherein the amplifier (100, 200) further comprises: a power amplifier circuit electrically coupled to the overdrive shaping circuit, the power amplifier circuit configured to receive a harmonic shaped signal from the overdrive shaping circuit, wherein the power amplifier circuit includes a switchmode amplifier configured to amplify the harmonic shaped signal, and means to increase the output impedance of the switchmode amplifier; and an output coupled to the power amplifier circuit, the output configured to output a signal amplified by the switchmode amplifier. a power amplifier circuit electrically coupled to the overdrive shaping circuit, the power amplifier circuit configured to receive a harmonic shaped signal from the overdrive shaping circuit, wherein the power amplifier circuit includes a switchmode amplifier configured to amplify the harmonic shaped signal, and means to increase the output impedance of the switchmode amplifier; and a switchmode amplifier configured to amplify the harmonic shaped signal, and means to increase the output impedance of the switchmode amplifier; and an output coupled to the power amplifier circuit, the output configured to output a signal amplified by the switchmode amplifier.