An audio amplifier including a non-inverting amplifier stage that provides linear amplification without loop feedback for low distortion audio systems. The amplifier stage includes a triode vacuum tube or a triode connected pentode vacuum tube and a P channel field effect transistor (FET). The vacuum tube and the FET are connected in a series combination in which the source of the FET is connected to the cathode of the tube through a suitable resistance. The drain of the FET is connected to a negative voltage and both the gate of the FET and the grid of the tube are at DC ground potential. The input signal to be amplified is fed into the gate of the FET and the output is taken from the plate of the tube which is supplied with a positive voltage through a suitable load. In most applications the grid of the tube is connected to ground, however in some applications the grid may serve as an extra inverting input.
An improved transimpedance amplifier includes a common cathode-connected vacuum tube first stage, coupled to a common-drain-connected MOSFET second stage, and an optional common drain-connected MOSFET third stage. Preferably, capacitive feedback is coupled from the output of the second stage to the input of the vacuum tube stage, to control the transimpedance of the amplifier. The circuit takes advantages of the low stray inter-electrode capacitances, low delay and transit times of the vacuum tube and the high transconductance of the MOSFET second and optional third stages, in a way complementary to one another to form a high transimpedance amplifier whose characteristics are controlled almost exclusively by the feedback capacitance or other feedback impedance, rather than by gain and stray capacitance terms of individual devices. The resulting transimpedance amplifier is useful in a number of applications, for example, in audio preamplifiers and audio power amplifiers.
The invention provides a high power, low distortion, high efficiency ampler design incorporating a high efficiency switching amplifier used in conjunction with a linear difference amplifier. The high efficiency switching amplifier, typically of full or half bridge design, is designed to generate a high efficiency, arbitrarily formed, wave portion such as a square wave. The high efficiency waveform is scaled down and is compared to a desired reference, such as a sinusoid. The output of the comparison is the analog difference (mathematical subtraction) between the reference waveform and the scaled-down switch amplifier output wave. This "difference" signal is then used to drive the linear difference amplifier which simply scales the signal linearly. The two power signals, one from the switching amplifier and the other from the linear difference amplifier, are then summed magnetically. To permit a low harmonic output, the input signals to the switching amplifier and the reference are locked together in frequency.
An audio power amplifier for general audio and sound reinforcement use, or musical amplification, stringed or otherwise, which combines the sonic properties of vacuum tube amplification with the modern technology of solid state electronics, with its attendant advantages.
A musical amplifier that includes a vacuum tube and a transistor. The vacuum tube is connected to the gate of the transistor, so that the current flow through the transistor is controlled by the vacuum tube. According to one example of the invention, the vacuum tube-transistor arrangement is set up in a "push-pull" arrangement, where a vacuum tube-transistor combination controls positive voltages, and another vacuum tube-transistor combination controls the negative voltages delivered by the system, the system output being at approximately zero voltage when not under load. Also, the use of the "Edison effect," referred to as "thermionic emission" from vacuum tubes to variably regulate output transistor bias current resulting in substantially reduced total harmonic distortion is also disclosed.
