Hi,
I am trying to modify a circuit for better results. It uses electret condenser microphone for input and is preamplified by general purpose lm381-1 amplifier. The problem is that the circuit is powered by rectified ac mains voltage which produces a small in uV, a ripple of 120Hz frequency, which is destroying the output which is fed to another amplifier. I have tried bypassing capacitors to no success. Then I've tried feeding the inverting input of the lm381-1 amplifier which was previously ground, with the power supply, which is also feeding the electret condenser microphone via a similar capacitor rating from which the dc input from mic is isolated and fed into the non inverting input of lm381-1. The idea is to cancel the noise 120hz signal. It is working in theory in that required noise cancellation is taking place, but unfortunately the two signals are not in phase reducing the efficiency.
Any idea how I can improve the result. I think the resistor and capacitor and mic are producing a phase change, and my one capacitor for inverting input is not matching it. Any help how to improve the result?
I am trying to modify a circuit for better results. It uses electret condenser microphone for input and is preamplified by general purpose lm381-1 amplifier. The problem is that the circuit is powered by rectified ac mains voltage which produces a small in uV, a ripple of 120Hz frequency, which is destroying the output which is fed to another amplifier. I have tried bypassing capacitors to no success. Then I've tried feeding the inverting input of the lm381-1 amplifier which was previously ground, with the power supply, which is also feeding the electret condenser microphone via a similar capacitor rating from which the dc input from mic is isolated and fed into the non inverting input of lm381-1. The idea is to cancel the noise 120hz signal. It is working in theory in that required noise cancellation is taking place, but unfortunately the two signals are not in phase reducing the efficiency.
Any idea how I can improve the result. I think the resistor and capacitor and mic are producing a phase change, and my one capacitor for inverting input is not matching it. Any help how to improve the result?
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