笔者最近购买了一台至高212B型功放,开始试听时声音完美,高中低音均表现不错,无噪音污染。但放音两天后出现了交流声,时大时小,且不随音量电位器变化。有时开机一段时间后出现,有时则开机便有。开机检查,因其交流声不受音量电位器控制,所以应重点检查功放后级。此类功放 Recently, I have purchased a high 212B amplifier, the perfect sound when you start the audition, high school bass are doing well, no noise pollution. However, after two days of playback, there was a humming sound, which was small and not changing with the volume potentiometer. Sometimes boot after a period of time, sometimes boot it. Boot check, because the hum is not volume potentiometer control, it should focus on checking the amplifier level. Such amplifier