We often encountered in project audio signal collection and processing, we do today one of the most simple audio collection module, its circuit was in our last class of the transistor amplifier circuit of an improvement, in the lesson on the basis of the transistor amplifier circuit, the output signal with electret microphone, output and cut-off frequency at around 20 KHZ RC low-pass filter circuit, filter circuit to filter out noise signal frequency in more than 20 KHZ,

Lesson about triode amplifier link below:

https://www.bilibili.com/read/cv5848391? The from=articleDetail


Design of the circuit principle diagram, as shown by sensors to obtain a small signal communication, a triple tube amplifier circuit amplified signal before output:




Can't wait to play board, manual welding to a sample test:




OSC482 by LOTO oscilloscope to measure the output signal of the enlarged:





Can also observe the transistor amplifier circuit of small signal amplification effect, at the same time to map out the large signal FFT spectrum:




The PC software comes with FFT spectrum drawing of oscilloscope function, according to the parameters of the video set up, you can automatically draw FFT spectrum test signal, the distance from one or two meters away from the normal voice can clear acquisition and display, in order to intuitive, below is made of stainless steel spoon hitting my ceramic cup sound waveform, originally receiver receiving voice is converted into voltage is small, put it through the transistor amplifier circuit is around 70 times, the oscilloscope can be clearly shows:




By FFT spectrum analysis found that the spoons and the pounding of ceramic cup, will produce a frequency of 2 k audio,
Recorded video process is as follows:

https://www.bilibili.com/video/BV1X5411x7cS/

Don't know why not come in video, I had to put the video link above,

Started the experiment we did not add the RC low-pass filter circuit on the output side, but directly measured with the oscilloscope, but we observed in the PC software interface measurement of the output signal is drowned out by a lot of noise signal, and not particularly intuitive observation to the output of the signal to enlarge, so we by designing a simple RC low-pass filter circuit to get rid of the noise is greater than the voice signal frequency, signal is submerged by noise figure as shown in the figure below:




About the RC low-pass filter we also talked about in class 3, not familiar with the guest officer who can under reference:

https://www.bilibili.com/read/cv5748656? The from=articleDetail


We use the practice of the RC low-pass filter parameters:


Finally offer the principle diagram of hurry finishing, will be advised and model for the subsequent cabling:




Is the most on the left side of the electret microphone not horn,