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I have built the blue circuit above for my microphone but the one of the problems I'm facing is that when I connect it to my laptop's audio input, it creates a humming sound. My assumption is there is a lot of noise whenever I pug it into my laptop.

Does anyone know why this is happening? Thank you for your help in advance.

Vipul Kumar
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    I fixed a lot of your grammatical errors. It's fine if English isn't your first language. However, Google Translate does a fair job in helping you with that. Now, back to your question: Have you done anything to debug this, i.e. making other modifications on your own, etc.? Circuits that you find online won't provide a solution for every single application. They're supposed to give you an idea of its functionality. It's up to you to make any modifications necessary to get it working the way you want it to. Did that circuit online specifically say that it will work for your laptop? –  Dec 24 '18 at 18:23
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    (1) Does the noise go away when you turn the volume down to minimum. (2) Does the microphone work at all? Please put this information in your question and not in the comments. Use the "edit" link under your question. – Transistor Dec 24 '18 at 18:33
  • Move your hand over the circuit; does this affect the level of the hum? Turn off all the room lights. Does this affect the hum? – analogsystemsrf Dec 25 '18 at 00:42
  • 1)yes noise go away when pot is all the way down – Vipul Kumar Dec 25 '18 at 14:03

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Do you use shielded audio cable between the mic and preamp? Ordinary non-shielded wires would be antennas that pickup mains hum and other interference.

Your very simple preamp has the resistor that powers the mic directly at the power supply that might produce hum when charging. That resistor should be fed from an RC filter.

Audioguru
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