A microphone system includes a microphone and a pre-amplification conditioning circuit configured within a housing and comprising a pair of matched JFETs configured in a differential pair with common-source configuration and, when biased, are operable to receive and amplify the differential microphone output signal. The microphone further includes a pair of BJTs configured as a complimentary feedback transistor pair with each of the pair of BJTs coupled in parallel to a corresponding one of the pair of matched JFETs, and a current sink coupled to the matched JFETs and corresponding emitter electrodes of the BJTs and operable to maintain a fixed total direct current through each of the matched JFETs and BJTs, which reduces the JFETs corresponding electrical load, reduces signal noise, and increases a maximum amplified microphone output signal level at the drains of the matched JFETs.

An amplifier stage uses a loaded transistor amplifier circuit including a load that causes greater second order harmonic distortion energy than third order harmonic distortion energy to be produced in said loaded transistor amplifier circuit for amplifying a source audio signal to produce an audio output signal. The spectrum of the fundamental orders of harmonic distortion is adjusted to improve perceived sound quality or listening enjoyment.

Multiple example valve amplifiers are provided. A first example valve amplifier is provided which comprises (i) a valve power amplifier switchable between a high-power mode and a low-power mode and (ii) a loudspeaker simulator circuit, the valve amplifier being configured such that the valve power amplifier drives the loudspeaker simulator circuit in the low-power mode. A second example valve amplifier is provided which comprises a switched-mode power supply, SMPS, system), the SMPS system comprising (i) an SMPS and (ii) circuitry configured to enable an output impedance of the SMPS to be switched between first and second output impedances, the first output impedance being lower than the second output impedance.

An amplifier stage uses a loaded transistor amplifier circuit including a load that causes greater second order harmonic distortion energy than third order harmonic distortion energy to be produced in said loaded transistor amplifier circuit for amplifying a source audio signal to produce an audio output signal. The spectrum of the fundamental orders of harmonic distortion is adjusted to improve perceived sound quality or listening enjoyment.

A musical instrument preamplifier includes a n-type JFET and a pnp current mirror connected to the drain side of the JFET. The pnp current mirror includes two pnp transistors. The current mirror is configured to control the current to independently set the operating point of the JFET and the output. An npn transistor is connected to one of the pnp transistors of the current mirror to form an inverted Sziklai pair. An auto-bias network is connected between the npn and pnp transistors that form the Sziklai pair.

A microphone system includes a microphone and a pre-amplification conditioning circuit configured within a housing and comprising a pair of matched JFETs configured in a differential pair with common-source configuration and, when biased, are operable to receive and amplify the differential microphone output signal. The microphone further includes a pair of BJTs configured as a complimentary feedback transistor pair with each of the pair of BJTs coupled in parallel to a corresponding one of the pair of matched JFETs, and a current sink coupled to the matched JFETs and corresponding emitter electrodes of the BJTs and operable to maintain a fixed total direct current through each of the matched JFETs and BJTs, which reduces the JFETs corresponding electrical load, reduces signal noise, and increases a maximum amplified microphone output signal level at the drains of the matched JFETs.

A microphone system includes a microphone and a pre-amplification conditioning circuit configured within a housing and comprising a pair of matched JFETs configured in a differential pair with common-source configuration and, when biased, are operable to receive and amplify the differential microphone output signal. The microphone further includes a pair of BJTs configured as a complimentary feedback transistor pair with each of the pair of BJTs coupled in parallel to a corresponding one of the pair of matched JFETs, and a current sink coupled to the matched JFETs and corresponding emitter electrodes of the BJTs and operable to maintain a fixed total direct current through each of the matched JFETs and BJTs, which reduces the JFETs corresponding electrical load, reduces signal noise, and increases a maximum amplified microphone output signal level at the drains of the matched JFETs.

A circuit has an input and a two-wire output. The circuit is designed for use with HTPE transducers and comprised of four stages. The first stage is a charge amplifier based on operational amplifier, the second stage is a 1-pole passive low-pass filter, the third stage is an active 2-pole low-pass filter based on two JFETs, and the fourth stage is an emitter follower comprising two bipolar junction transistors connected to each other in Darlington configuration.

A circuit has an input and a two-wire output. The circuit is designed for use with HTPE transducers and comprised of four stages. The first stage is a charge amplifier based on operational amplifier, the second stage is a 1-pole passive low-pass filter, the third stage is an active 2-pole low-pass filter based on two JFETs, and the fourth stage is an emitter follower comprising two bipolar junction transistors connected to each other in Darlington configuration.

An amplifier stage uses a loaded transistor amplifier circuit including a load that causes greater second order harmonic distortion energy than third order harmonic distortion energy to be produced in said loaded transistor amplifier circuit for amplifying a source audio signal to produce an audio output signal. The spectrum of the fundamental orders of harmonic distortion is adjusted to improve perceived sound quality or listening enjoyment.