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 circuit including a JFET or MOSFET transistor, one input of an impedance network connected to the transistor's gate, a terminal of a source resistor connected to the transistor's source, another terminal of the source resistor connected to ground, a bypass capacitor connected in parallel to the source resistor, one terminal of a load resistor connected to the transistor's drain, VCC_LOW connected to another terminal of the load resistor, an input of an op-amplifier connected to the transistor's source through a bi-directional low-pass-filter, another input of the op-amplifier connected to reference voltage, an output of the op-amplifier connected to another terminal of the input impedance network through an LPF, an energy detector connected to the transistor's drain via a coupling capacitor, an LPF connected to the energy detector output, and an LPF connected to the output of the energy detector, the input impedance network connected to a microphone.

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.

A microphone circuit including a JFET or MOSFET transistor, a terminal of an input-impedance-network connected to the transistor's gate, one terminal of a source resistor connected to the transistor's source, and another terminal connected to ground, a bypass capacitor connected in parallel to the source resistor, one terminal of a load resistor connected to the transistor's drain, a charge-pump generating low-voltage connected to the second terminal of the load resistor, and an inverted voltage connected to a power supply terminal of an op amplifier, one input of the op-amplifier connected to the source terminal of the transistor through a bi-directional low-pass-filter, another input connected to a reference voltage, one power supply terminal connected to the inverted voltage, another power supply terminal connected to main supply voltage, an output terminal connected to another terminal of the input-impedance-network through a low pass filter, where the input-impedance-network connected to a microphone.

An amplifier comprising a FET transistor, a bias resistor having a first terminal connected to a gate terminal of the FET transistor, a load resistor having a first terminal connected to a D terminal of the FET transistor, a DC-to-DC step-down converter with an input terminal connected to a supply voltage, and an output terminal connected to a second terminal of the load resistor, a two-pin current-to-voltage converter with a first pin connected to an S terminal of the FET transistor and a second pin connected to ground, and a comparator having a first pin connected to a positive supply voltage, a second pin connected to a negative supply voltage, a third (output) pin connected to a second terminal of the bias resistor, a fourth pin connected to a reference voltage, and a fifth pin connected to the first pin of the current-to-voltage converter.

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.

Disclosed is a class-D amplifier including a first output circuit, a first capacitor, a pulse width modulator, and a slew rate limiting amplifier. The first output circuit includes first and second switching devices that are connected in series between first and second power supply lines. The first capacitor is connected between the first and second power supply lines. The pulse width modulator generates a pulse width modulated switching signal based on a triangular wave and an audio signal, and provides the switching signal to the first output circuit. The slew rate limiting amplifier is connected to an input part of the pulse width modulator to which the audio signal is provided, and limits a slew rate of output. The sound-producing device is connected in series to an inductor connected to a first output node of the first output circuit. The sound-producing device and the inductor constitute an LC filter.

Methods, apparatus, systems, and articles of manufacture are described to regulate an amplifier. An example apparatus includes a modulator; a comparator having an input and an output, the input of the comparator coupled to an output of the modulator; a first switch having a voltage source terminal and a second terminal; a second switch having a voltage source terminal and a second terminal; a resistor having a first terminal and a second terminal, the first terminal of the resistor coupled to the second terminal of the first switch and the second terminal of the second switch; a capacitor having a terminal coupled to the second terminal of the resistor; and a buffer having an input and an output, the input of the buffer coupled to the terminal of the capacitor and the second terminal of the resistor, the output coupled to an input of the modulator.

Methods, apparatus, systems, and articles of manufacture are described to regulate an amplifier. An example apparatus includes an integrator, an input terminal of the integrator coupled to a terminal of a first resistor circuitry and an output terminal of the integrator coupled to a capacitor; an output stage, an input terminal of the output stage coupled to the output terminal of the integrator; second resistor circuitry, a first terminal of the second resistor circuitry coupled to the output terminal of the output stage, a second terminal of the second resistor circuitry coupled to the terminal of the first resistor circuitry and the input terminal of the integrator; and third resistor circuitry, a first terminal coupled to the terminal of the first resistor circuitry, the second terminal of the second resistor circuitry, and the input terminal of the integrator.

Disclosed is a microphone for capturing sound. The microphone comprises a capsule configured for receiving a sound input and converting the sound input into an output signal, the output signal comprising an output voltage V_CA, the output voltage V_CA having a first non-linearity at least at sound pressure levels (SPLs) above a first threshold. The microphone comprises a pre-amplifier configured for receiving the output signal from the capsule and generating an output voltage V_PA, the output voltage V_PA having a second non-linearity for at least a first input signal level. The microphone is configured for providing that the capsule and the pre-amplifier generate similar amounts of the first non-linearity and of the second non-linearity, respectively, and where the first non-linearity and the second non-linearity are in anti-phase to each other, thereby counter-balancing each other and thereby linearizing an output signal V_MI of the microphone.