Main prevention and control measures for electromagnetic interference in the PCB wiring of power amplifier module and circuit:
1. Reduce input impedance.
Electromagnetic waves are mainly picked up by wires and PCB board wiring, and under certain conditions, the electromagnetic waves picked up by wires can be considered as constant power. According to the derivation of P=U ^ U/R, the induced voltage is inversely proportional to the square of the negative value, indicating that achieving low impedance in amplifiers is beneficial for reducing electromagnetic interference. For example, if the input impedance of an amplifier is reduced from 20K to 10K, the induced noise level will decrease to a level of 1/4. Active speaker audio sources mainly include computer sound cards, portable speakers MP3, This type of audio source has strong carrying capacity, and appropriately reducing the input impedance of active speakers has a very weak and difficult to detect impact on sound quality. During the experiment, the author attempted to reduce the input impedance of active speakers to 2K, but did not feel any changes in sound quality, and long-term operation did not show any abnormalities.
2. Enhance high-frequency anti-interference capability
In response to the fact that most stray electromagnetic waves are mid to high frequency signals, a magnetic capacitor is added to the input of the amplifier to ground. The capacitance value can be selected between 47-220P, and the frequency inflection point of the capacitor with a capacitance value of several hundred picofarads is two to three orders of magnitude higher than the audio range. The impact on the sound pressure response and listening experience within the effective listening frequency range can be ignored.
3. Pay attention to the installation method of the power transformer
Use high-quality power transformers, try to widen the distance between the transformer and PCB, adjust the orientation between the transformer and PCB, and keep the transformer and amplifier sensitive end away from each other; The interference intensity of El type power transformers varies in different directions. It is important to avoid aligning the Y-axis direction with the strongest interference intensity with the PCB as much as possible.
4. The metal casing must be grounded
For HIFI independent amplifiers, products with design specifications have an independent grounding point on the chassis, which is actually reduced by the electromagnetic shielding effect of the chassis to reduce external interference; For common active speakers, the metal panel that also serves as a heat sink needs to be grounded; The casing of the volume and tone potentiometer should be grounded as much as possible if conditions permit. Practice has proven that this measure is very effective for PCBs working in harsh electromagnetic environments.
Signal Power Amplifier manufacturer from China
