The insiders have always been very clear that the post-stage part of the combined power amplifier below 10,000 yuan is not worth considering. Especially for the new combined power amplifier, the post-stage is seriously shrunk and the power is falsely reported, but it is extended to all the combined power amplifiers.

In fact, there was no such thing as cutting corners and falsely reporting power many years ago. It is now found that the rivers and lakes are not what they used to be, and commercial fraud is everywhere. A small flagship power amplifier with a value of tens of thousands of years ago was changed to a pure post-level, 60W×3+22W×4, and HTPC+D2 was used to push 7 large boxes to taste! . In the absence of a subwoofer, I feel a strong sofa**. In contrast, today, in so many audio forums, what I talk about is “can’t push”, and many manufacturers keep the standard of 100-200W×7. Power, but there is still no way to push it, which keeps me depressed and incomprehensible. I will no longer analyze why the manufacturer should do this. The post-amplifier is to use a lot of copper and aluminum! Anyone who is a little older should know that copper and aluminum were just a little more expensive than iron before, and they are not valuable. Ordinary people have bronzes everywhere, but what about today?

Many friends do not quite understand what kind of performance the power amplifier really wants to achieve, and mistakenly believe that as long as the power is large enough, it is king, and they do not know what is the difference between the post-stage and pure post-stage amplifiers of the combined amplifier. Those friends say "control power", "analytic power", etc., but they don't know how the power amplifier can achieve these performances.

A friend once consulted me about a 2-channel pure final stage, and I proposed two extremely critical concepts, “Damping Coefficient” and “Slew Rate”, which are not familiar to everyone.

The basic index of the power amplifier: rated power.

Today, American and European power amplifiers will be marked with rated power. Old power amplifiers are also marked with rated power. Generally, the power is under low distortion (such as 0.015%, power measured at 20-20kHz, and more advanced power amplifiers are measured at 0.008%). To have a strong output power, a strong power supply support is absolutely necessary! The amount of power reflects the strength of the sound, which is the sense of quantity.

The second basic indicator of the power amplifier: various degrees of distortion.

The above has shown that this is directly related to the size of the power. When the power of the power amplifier is large enough, and only a small part of its power is used, the distortion at this time will be much smaller.

The rear stage of the combined power amplifier often uses only a pair of power tubes. The pairing of the power tubes has a great influence on the distortion. The previous advanced power amplifiers are directly paired to the device production line (for example, the distortion of the old power amplifier is very small. Ten thousand yuan is equivalent to today's one hundred thousand yuan), the cost is very high, today's tens of thousands of power amplifiers will not do this. Today, when the power tube is not well matched, it is necessary to use a small power to reduce the distortion under high power. The degree of distortion reflects the quality of the sound, that is, the texture.

An important indicator only available in advanced power amplifiers: damping coefficient.

In addition to power and distortion, an advanced power amplifier has a great relationship with the internal resistance of the output to the ability to control bass quality. To ensure a very small output impedance in a high-current environment, you must first have a high-quality high-power transformer, a high-current rectifier circuit, and a powerful capacitor filter circuit. These advanced power amplifiers are never available due to space and cost constraints. The pure power amplifier is several times that of the combined power amplifier in this respect. Secondly, in order to achieve a strong output power and a very small transistor output impedance, the pure post-stage power amplifier uses several pairs of power tubes to work in parallel, and its control force is also several times stronger than that of the combined power amplifier, and the combined power amplifier only uses A pair of output power tubes (see how many pairs of power tubes can be installed with such a small radiator?).

Of course, the thickness of the speaker wire, the copper content and the quality of the terminal also have a direct impact on the damping coefficient. The damping coefficient reflects the quality of the control of the bass by the power amplifier, that is, the control force.