How Does an Power Amplifier Amplify Signals?

The "source" of the audio system, whether it is in analog or digital form, is a block that receives or plays music content for the professional audio sound system that cannot produce music by itself. Only with the source to play or receive music signals can we listen to the speaker system. To music. However, we also mentioned that the source circuit or equipment cannot provide enough power to drive the speakers or even the earphones, so the audio system also needs a "power amplifier" to drive the speaker device to emit sound.

 

As the name implies, "power amplifier" is to expand the signal of the signal source to drive the speaker device, but in fact the work performed by the amplifier is not to expand the signal. To put it more clearly, "the signal itself cannot be expanded." We can use passive attenuation components such as resistors to "loss" the original signal strength, but in fact there are no components or even circuits that can "amplify" the signal; then some friends must doubt how the power amplifier amplifies the signal. What?

 

Said that the real working method of the expansion circuit is not to directly amplify the signal, but to "copy" the higher voltage or larger current signal according to the original signal. The setting of the circuit determines the signal output. Generally speaking, to drive the speaker load conditions, the voltage and current of the source signal must be increased. The circuit design of the power amplifier will increase both the voltage and current when the signal is copied, which is called "gain" in electronics. .

 

However, in order to avoid making circuits and components work under too harsh conditions to obtain better performance, such as low distortion and low noise, the voltage gain and current gain circuits are usually made separately. In addition, common operating functions of power amplifiers such as source selection, volume control, and high and low sound quality control are planned in the voltage gain circuit block; because the music signal is processed in this low current stage, it will be better than in the high current situation. The next step is to achieve better results and lower costs.

 

Therefore, the voltage gain and control circuit will be planned in the front part of the circuit architecture. It used to be called the "pre-stage" circuit. The most important thing of the pre-stage circuit is the volume control of the audio system, and the volume control seems simple. The matter is actually the most learned part of the audio circuit. We will discuss it in another article in the future. Although the front-end circuit can copy the signal from the source into a signal with sufficient voltage, the weak current is still not enough to drive a low-impedance and heavy-load speaker, so "current gain" is also needed.

 

The circuit responsible for current gain is also to copy the signal output from the previous stage, but it is copied into a "large current" signal, which is generally called the latter stage or "power amplifier"; in most cases, power amplifier circuits A small voltage gain is also provided to improve dynamic performance. Generally speaking, the larger the output current of the power amplifier circuit is, the better it can drive the loudspeaker with heavy load (the lower the impedance, the heavier the load), especially the impedance of the loudspeaker will change with frequency.

 

Therefore, the power amplifier circuit requires a power supply with sufficient voltage and current. Therefore, a large transformer and a large number of filter capacitors are very important, but they will also increase the production cost. That is one of the reasons why the performance of the power amplifier is generally measured by weight. ; A power amplifier with a huge output power is usually relatively large in size and emits a certain amount of heat when working. However, the technology of switching power power amplifier and Class D power amplifiers  and digital DSP power amplifiers is becoming more and more mature nowadays, and some high-power amplifiers can already be light and cool.

 

FP10000Q 10000 watt 4 channel switching power amplifier

DA series class D muti channel power amplifier

D10Q 4 channel digital DSP power amplifier

The other is the advanced power amplifier style. It is a product that separates the front stage circuit and the power amplifier circuit into a single piece of the front stage amplifier and the rear stage/power amplifier, allowing audio players to match each other more freely to obtain the required functions, Sound performance and adaptability of speaker matching. However, due to changes in consumer trends, there are now advanced integrated power amplifiers with performance comparable to that of the front and rear stages, and it is not necessary to bother with the combination of front and rear amplifiers.

 

There are still many technical problems in the pre-stage and post-stage power amplifier circuits, such as the aforementioned pre-stage volume control technology, or the post-stage power amplifier circuit is divided into different working methods such as Class AB, Class TD, and Class D. In the future Individuals will also discuss the topic separately. If you have any questions that you want to be included in the discussion, or if there are errors in the article that need to be corrected, you are welcome to enlighten me.