3 principles for preventing hum in power amplifiers

Some power amplifiers “buzz” when they are turned on, and now introduce several methods of handling: 1. Power and grounding point treatment Many power amplifier filter capacitors are too small, four are only about 10000μF, and a 0.22μF CBB capacitor is connected at both ends. Strength and high-frequency resolution. Some power amplifiers still have AC hum even after the above treatment, which may be the improper grounding point. Generally, the grounding point should be selected near the filter capacitor, and the 'one-point grounding method' should be used. 2. Output stage If the static potential of the output stage deviates from the zero point, a great hum will be generated. At this time, there may be a problem with the zero resistance or the output to the tube. You can carefully adjust the potential of the output point of the power amplifier, which should be below 100mv. At zero, you should carefully check whether some components of the power amplifier, such as the tube, are damaged. 3. Pre-amplification part First, short-circuit the input end of the pre-amplifier to ground to see if the noise disappears. If the noise disappears, it can be assumed that the noise originates from the input signal line, and it can be replaced by a three-core shielded wire. Note that the shielding layer can only be grounded at one end. . In addition, the coupling capacitor should use a capacitor with small leakage, such as tantalum capacitor, MKP capacitor, etc., and the volume potentiometer shell should be grounded.