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How to choose and use power amplifier correctly?

2020-08-11

How to choose and use power amplifier correctly?

 

Power amplifier, referred to as "power amplifier". In many cases, the rated output power of the host is not up to the task of driving the entire audio system. At this time, a power amplifier must be installed between the host and the playback device to supplement the required power gap, and the power amplifier plays a role in the entire audio system. The pivotal role of "organization and coordination", to some extent, controls whether the entire system can provide good sound quality output.

 

So how to choose and use the power amplifier correctly?

 

 

 

01 How much power amplifier should I choose?

 

Before choosing a power amplifier, the first problem encountered is how much output power to choose. This is not only related to the effect and stability of a sound system, but also related to the cost of the system.

 

Everyone knows that there are many ways to express the output power of a power amplifier, including rated output power, music power, and peak power. They can differ by several times, some ten times, and the value of these output power is inversely proportional to the load impedance. That is, the smaller the load impedance, the greater the output power of the same power amplifier. In theory, the impedance is reduced by half, and the output power is doubled.

 

First, let's define the rated output power of the power amplifier. The so-called rated output power means that under a certain load impedance (usually 8Ω) and a certain harmonic distortion (according to the manufacturer’s 0.1% or 0.3%, etc.), a sine wave signal is fed at the input end and at the output end On the load, the maximum power obtained is calculated using the formula P=U2/R.

 

Secondly, how to choose an amplifier in a hall? In practical applications, we generally do not directly choose a power amplifier with 400W output or 800W output. Because of the size of the power amplifier output, it is not the same thing whether the sound in the hall that we care about is loud enough. The output power of the system's power amplifier, in terms of type, some are pushing full-frequency main channel speakers, some are pushing and pulling audio and video speakers, some are pushing stage return speakers, and some are pushing subwoofer speakers. The number and functions are very different. At the same time, it is related to the sensitivity of the speakers being pushed, and it also has a lot to do with the acoustic environment of the hall.

 

The influence of so many factors on the sound pressure level (usually speaking the sound is not loud) can be quantified and characterized by a formula: W=10(LP-LS+20lgr)/10

 

LP: The required sound pressure level dB at the test point (the speaker radiation distance);

LS: Speaker sensitivity dB, given by speaker parameters;

R: the distance m from the speaker to the test point, also called the speaker radiation distance;

W: The driving power required by a single speaker;

 

We can use this as a basis to reasonably determine the power output of the power amplifier. It should be noted here that the formula generally determines the output power of the main channel power amplifier. The stage return speakers can be determined by 30%-50% of the main channel power, the output power of the subwoofer amplifier can be determined by 100%-150% of the main channel power, and the power amplifier power of the auxiliary speakers can be determined by 50% of the main channel power. %-100% OK.

 

It must never be estimated and determined by imagination. If you use this method to determine, the consequences will either be wasted (the power is selected too large), or the effect will not be achieved, it is very easy to cause damage to the successful amplifier (the power is selected small), unless you are very experienced.


 

02 How to judge the power amplifier

 

For a power amplifier, many people often cannot judge its quality. Just relying on the indicators provided by the manufacturers are often similar and confusing, and depending on the price, in some cases it is not necessarily a good product if the price is high. Next, the author will talk about how to judge the quality of the power amplifier from the actual use. Of course, it is another matter to use the instrument to test the index.

 

Get an amplifier, we can simply judge from the following aspects:

 

1. Appearance and packaging

For the outer packaging of an amplifier, the first step is to see whether the packaging box is upright, whether the printing is exquisite, whether the information is complete (specification, origin, certification, etc.), and then whether the shockproof filling material of the packaging is environmentally friendly. Those that are well packaged, reasonable, and environmentally friendly can be considered good power amplifiers.

 

2. The appearance of the power amplifier

Check whether the surface treatment of the panel is fine, whether the shell plate is thick, whether the screws and screw holes are accurate, whether the knobs, connectors, and text printing are accurate and clear. If they are all good, the quality of the power amplifier can be considered good.

 

3. Turn on the power amplifier

Check whether the volume and weight of the toroidal transformer match the marked output power, and whether the appearance is rough, then check whether the filter capacitor is a genuine product, and whether the capacity and withstand voltage are sufficient (generally, the capacity is 10000uf, and the withstand voltage is 100-200v). Whether the wiring is clear and reasonable, especially the high-power tube: Look at its number, with the increase of output power, the number of high-power tubes can be configured from 8 to 24, or even more; secondly, look at its packaging form, whether it is metal packaging , The plastic package is slightly smaller in terms of power; thirdly, whether it is a product of a well-known manufacturer; and so on.

 

4. Judge the protection circuit

See if the protection circuit module is relatively simple, the regular protection circuit has functions such as overcurrent, overvoltage, overtemperature, and time delay. The poor power amplifier only has a power-on delay, no other protection measures, and the circuit is very simple.

 

5. Power on

The fan has low noise, no transformer vibration, and no other abnormal sounds. On the contrary, the power amplifier is a bad product.



03 Amplifier and speaker connection

 

We know that the power amplifier is to amplify the audio signal to drive the speaker unit. But in practical applications, the problem is quite complicated. Why do you say that?

 

As you all know, speakers have the nominal power of speakers. In practical applications, the signal voltage is not a sine wave of a certain frequency, but can be decomposed into a complex wave of many harmonics, and its average power is not a sine wave. Average power under wave conditions; the output mode of the second power amplifier. We have analyzed three modes of stereo output, parallel output and bridge output. How should we choose? The output impedance of the third power amplifier and the input impedance of the speaker have different meanings. Is it the same good or is it better to choose a speaker with a small impedance as much as possible? and many more. Therefore, understanding the connection of power amplifiers and speakers is necessary to understand the power amplifier.

 

To sum up, in an audio system, to use a professional power amplifier, not only lies in the quality of the power amplifier, but also how to use the power amplifier correctly, how to use it with the sound and so on.


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