The cause of the current sound of the audio amplifier (I)

Many audio engineering parents are often plagued by the "current sound" of the amplifier. Most people think that the current sound is caused by poor grounding, so they try to ground the outer casing of the amplifier and even shield the entire amplifier with a metal cover. But the current is still sound, and there is no countermeasure. Everyone has different definitions of "current sound". First, find out which kind of "current sound" you encounter. In more than half of the cases, there is no problem with grounding. "Current sound" is not caused by static electricity. But looking at the descriptions of different friends, "current sounds" are:

Continuous noise

The loudness of the noise is quite stable

Usually low frequency noise

In the experience of all the friends, the "current sound" can be summarized in the following cases:

Power Ripplenoise, ie Humming

Pick-upnoise includes body pickup noise (Bodypick-up)

Layout or Groundingtopology

Bad ground noise (Groundnoise) and circulating ground (Groundloop)

Bad wiring and shielding strategy (Badwiringandshieldingstrategy)

Communication hum

The cause of the AC hum is the improper design of the power filter, or even cut corners, causing some of the AC signal from the mains to slip into the amplifier. This type of current sound is characterized by a very low frequency, which is very weak in most cases. It is only heard when the ear is attached to the speaker, and even if the volume is set to a minimum, the noise still exists.

The filter capacitor (tank), in addition to the larger the capacity, the smaller the equivalent series resistance (ESR). This is the most common type of current sound.

How to solve this kind of current sound? It depends on whether your amplifier uses an external or built-in transformer. If you use a built-in transformer, the situation is more complicated. You need to replace the tank with a capacitor with a larger capacitance value, or even increase the number of capacitors. When several capacitors are connected in parallel, their capacitances will be added, but this method will be limited by the space inside the machine and requires random strain.

Because the frequency of this noise is very low (100Hz), and usually very slight, these low-cost amplifiers can often get rid of the small-caliber speakers, but to detect the noise of the power supply, there is a very simple method, as long as When the amplifier is turned on, touch the diaphragm of the low-frequency unit by hand. If the vibration of the diaphragm of the speaker is still felt when there is no signal or the volume is adjusted to the lowest, this is a very obvious evidence of the AC hum.

If you are using an external transformer (such as a general mini amplifier), of course, the above methods are applicable, but there is another simpler method - replace it with a switching power transformer (SMPS), the problem will be solved!

I am very surprised! First of all, the sound quality of the switching power supply is not very bad, but the AC hum is solved in a single way, and the switching source transformer does have an immediate effect.