First, power and grounding point processing
Many power amplifier filter capacitors are small, four are only about l0000μF, and have a CBB capacitor of 0.22μF at both ends, which can not only reduce the hum of the power when it is static, but also improve the transient of the power when it is placed in large dynamics. Strength and high frequency resolution. Some power amplifiers may still have a grounding point even after the above processing, and the grounding point may be improper. Generally, the grounding point should be selected near the filter capacitor, and the "one-point grounding method" should be used.

Second, the output level

If the static potential of the output stage deviates from the zero point, it will produce a great humming sound. At this time, it may be a zeroing resistance or a problem with the output tube. The output point potential of the power amplifier can be carefully adjusted, which should be below 100mv. At zero point, you should carefully check whether some components of the power amplifier, such as the tube, are damaged.

Third, the preamplifier part

First, short the input end of the preamplifier to the ground to see if the noise disappears. If the noise disappears, the noise can be determined to be from the input signal line. You can replace it with a three-core shielded cable. Note that the shield can only be grounded at one end. . In addition, the coupling capacitor should use a small leakage capacitor, such as tantalum capacitor, MKP capacitor, etc., the volume potentiometer housing should be grounded.