First, the current hum of the power amplifier board
1. Barn the speaker into the power amplifier, turn on the power, move the position of the power transformer until the click is weakened, and then use a metal cover (which can be an iron case) and live fixed.
2. If the secondary extraction of the transformer is a cable, it should be disassembled and changed into a braided wire.
3. The negative end of the speaker output lead on the circuit board is soldered, and a low-noise solder can be found at the large-area grounded copper foil after the filter capacitor.
4. Increase or replace the filter capacitor.
5. Change the installation position of the power amplifier board, and place the heat sink between the transformer and the circuit board to act as a magnetic shield to reduce the current hum.
6. Appropriately change the component pin height, especially the feedback resistor and the coupling capacitor. The voltage amplifying parts composed of discrete components should also be noted, and their pin height is preferably 2 to 5.5 mm from the board surface.
Second, after the power amplifier
1. Take 1000pF ceramic dielectric capacitor and solder one on each diode in the rectifier circuit.
2. Take a film capacitor with a capacity between 220 and 1500pF and mix it between the signal input terminal and the ground. Use a capacitor with the smallest click sound; and play a familiar piece of music, without affecting the high frequency. The characteristics shall prevail.
The above noise prevention method is performed by cutting off the front input. It can also be used for noise reduction processing of preamplification.
Third, the buzz of the preamplifier
1. Disconnect the "+" end of the DC power supply line and string into the inductance of 100~300mH.
2. Use a plastic rod or bamboo chopsticks to clamp the input end of the sound source to the lead of the preamplifier board, and find a minimum sound to fix it.
3. Change the grounding point of the front and rear amplifier boards. If the two are connected by a shielded wire, the shielded mesh at one end of the shielded wire should be soldered to the input of the rear stage, while the other end is not grounded. The same is true for the wiring of the front and audio input connectors, and only ground at the input end of the audio source. In this way, a ground loop will not be formed, and the unpleasant hum will not be coupled.
Fourth, the preamp of the power amplifier
It mainly appears in the feedback tone circuit, especially the scaffolding, and the high frequency hum is serious. The solution is to shield it with a thin copper foil, or switch it to a passive attenuation tone circuit to reduce the click.
The above several noise reduction measures are limited to applications in transistors and integrated circuit power amplifiers. Of course, the design of the circuit board is critical, such as power supplies, audio signal routing, analog ground and digital ground, and so on.
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