一些体积小的廉价的晶体管便携式无线电接收机,其电路大体相同.经一级变频,两级中放和检波,再馈至音频激励级,而后经B类推挽输出级用变压器与扬声器耦合.这种接收机的音频部分电路示于图1.其输出音质不佳,而且当音量小时,有明显的交叉失真.低音输出(用三寸喇叭)几乎全被抑制,呈现出很大的低音畸变. Some small, inexpensive transistor portable radio receivers have roughly the same circuit and are first-frequency converted, two-stage drop-in and detector, fed back to the audio driver stage, and then coupled via a B-type push-pull output stage transformer to the speaker. The audio part of the receiver’s circuitry is shown in Figure 1. The output is poorly sound, and when the volume is small, there is significant cross-talk. The bass output (with the three-inch speaker) is almost completely suppressed, exhibiting a large bass distortion.