Tuesday, 29 October 2019

microphone - My simple audio amplifier circuit does not work



In previous experiments I've made circuits to transfer sound from electret microphone to a powered speaker. Now I'm doing my first experience with an Op-Amp to make the sound louder and to be able to hear it in a headphone. The Op-Amp I'm using is LM358N. Here is my circuit:


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I'm using the formula below, that I copied from the Internet for the non-inverting operation amplifier:


$$Gain = 1 + \frac{R2}{R1}$$


Given the resistor values of R1= 4.7 ohm , R2 = 150 ohm, my gain is about 32.9 times.


So here is the summary of information about my circuit:



  • V+ = 5v from USB

  • Capacitor : 0.1uF

  • R next to V+ : 4.7 Kohm


  • R1= 4.7 ohm

  • R2 = 150 ohm


But my speaker doesn't work when the op-amp IC is placed on the circuit. If the op-amp IC is inserted on it's socket, I can hear only "rett, rett" when I try to blow to the electret microphone. What is wrong here?




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