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笔者见许多随身听在进行机外现场录音时,均用原配有线话筒,由于话筒线只有一米左右长,显然录不出好的现场感,且操作很不方便。本文介绍的这套话筒是利用原机的调频波段接收,然后进行录音。由于采用了无线开路发射,因而可以将话筒放置高声源很近,且可以同时供多台接收机录音。电路如图所示。话筒信号放大部分用LM324中的二个作独立放大。为保证音质,放大后的信号经C6、R7、C7、R8组成的预加重网络送至调频立体声专用发射块BA1404的①和⒅脚调制。BA1404内部包含左右声道放大器,MPX平衡调制器,两个缓冲放大器,38kHz振荡器,1/2分频器,射频振荡器和射频放大器等。其工作电压在1～3V之间,故采用电阻降压,经LED稳压在1.7～2V之间,同时LED也可作为工作状态指示。
I see a lot of Walkman recording machine outside the scene, are equipped with the original microphone line, because the microphone line is only about one meter long, apparently did not record a good sense of the scene, and the operation is very convenient. This article describes the microphone is the use of the original machine FM band reception, and then recording. Thanks to its wireless open-circuit transmit- ments, it is possible to place microphones close to high sound sources and to record multiple receivers simultaneously. Circuit as shown. Microphone signal amplification part of the LM324 in two for independent amplification. In order to ensure the sound quality, the amplified signal is sent to the ① and ⒅ feet modulation of the BA1404 FM stereo emission block through the pre-emphasis network consisting of C6, R7, C7 and R8. The BA1404 contains the left and right channel amplifiers, MPX balanced modulators, two buffer amplifiers, 38kHz oscillator, 1/2 frequency divider, RF oscillator and RF amplifier. The working voltage between 1 ~ 3V, so the use of step-down resistor, the LED regulator between 1.7 ~ 2V, while the LED can also be used as an indication of the working status.