For decades, Class AB output stage has set a standard for high-quality sound power amplifiers. Although Class AB power amplifier is famous for its excellent sound quality, it does not make effective use of power. The output stage generates a lot of heat, and huge heat sinks and fans are needed to ensure that the output transistor inside the power amplifier is at a safe temperature. In order to get high power, more power is needed, but in the end most of the power becomes heat.
The other two common power amplifier technologies can achieve higher efficiency, but they both have defects. Class D switching power amplifier adopts pulse width modulation (PWM) technology, which is very efficient, but many "pure" Class D products compromise on sound quality. The way to improve the efficiency of class H design is to "track" the input signal in real time by modulating the input signal and power supply voltage, and provide the best output voltage. However, Class H can only achieve the highest efficiency in a relatively limited dynamic range.
The basic concepts of Class D and Class H have a history of several decades, and they have not been patented. However, the circuit design to realize these basic concepts can be patented, such as Lab.gruppen's breakthrough TD class power amplifier technology. TD is the abbreviation of "tracking D class", that is, the power supply tracks audio signals at all frequencies and provides the required on-orbit voltage while retaining extra margin. Although the final output stage is still class AB, the principle of high-speed switching of class D power amplifier is added. The whole audio channel is still in analog mode, and the signal will not be converted into digital pulse and filtered like class D power amplifier. At the same time, there is no moire effect of PWM output stage.
TD technology of Lab.gruppen can work well under all loads. The output frequency response has a flat output even if the load is as low as 2 ohms. The output can be bridged, with high reliability and no RF interference. The power amplifier has high efficiency, which reduces the requirement of heat dissipation to the maximum extent while outputting high power, while the sound quality is still AB.
TD technology has existed since 80 years ago. The former stage is PWM/PFM modulation and the latter stage is linear filtering. This technique has no problem with resistive loads, but; Low power factor operation and poor stability! Please look at the mountain map of horn frequency response-impedance characteristics.