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一台HA834免提电话机,用户反应在使用免提方式通话时发生反馈啸叫,如果将音量电位器RP_3关小消除啸叫,扬声器声音将减小,调整输入灵敏度电位器RP_1减小啸叫,又使送话声音减小,影响正常使用。仔细分析其电原理图发现,该机是采用同相、反相输出相互抵消的原理来消除其免提方式时的反馈啸音。原理图如附图所示。由话筒B_4送来的信号,经
A HA834 hands-free phone, the user reaction feedback during the hands-free speaker feedback howl, if the volume potentiometer RP_3 off small eliminate howling, the speaker sound will be reduced to adjust the input sensitivity potentiometer RP_1 howl , But also to send the voice to reduce the impact of normal use. A careful analysis of its electrical schematic found that the aircraft is the use of inphase and anti-phase output offset each other to eliminate the feedback hands-free feedback howl. Schematic as shown in the figure. The signal sent by the microphone B_4, via