Three Principles for Preventing Amplifier Hum

Some amplifiers make a buzzing sound when they are turned on. Here are some solutions:

1. Power supply and grounding point processing

Many amplifier filter capacitors are too small, some are only about 10000μF, and a 0.22μF CBB capacitor is connected at both ends of the amplifier, which can not only reduce the AC noise of the amplifier in static state, but also improve the transient strength and high-frequency resolution of the amplifier in large dynamic state. Even after the above treatment, some amplifiers still have AC hum, which may be due to improper grounding point. Generally, the grounding point should be selected near the filter capacitor and the "one-point grounding method" should be adopted.

2. Output Stage

If the static potential of the output stage deviates from the zero point, a loud buzzing sound will be generated. At this time, there may be a problem with the zero adjustment resistor or the output tube. The output potential of the power amplifier can be carefully adjusted, which should be below 100mv. If the zero point cannot be adjusted, the power amplifier components such as the tube should be carefully checked for damage.

3. Pre-amplification

First, short-circuit the input end of the preamplifier to the ground to see if the noise disappears. If the noise disappears, it can be determined that the noise comes from the input signal line, which can be replaced with a three-core shielded line. Note that only one end of the shielding layer can be grounded. In addition, the coupling capacitor should be a capacitor with low leakage, such as a tantalum capacitor, MKP capacitor, etc., and the volume potentiometer housing should be grounded.