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Here's the schematics:

enter image description here

The circuit is powered by a 9V battery. There is a voltage divider that gives 4.5V between R4 and R5, this voltage is applied to the negative pole of the electret microphone (V2). The rest of the circuit is the first stage of an instrumentation amplifier built with a TL-082 op-amp and the condensers are there to remove the 4.5V bias before sending the signal to the mono jack.

The microphone by itself works perfectly, when it's connected to the amplifier the computer only gets a small noise. Could any you guys help?

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    \$\begingroup\$ I don't have access to my computer right now. The schematic is clearly visible and easily readable, what's the issue? \$\endgroup\$ Mar 12, 2017 at 22:37
  • \$\begingroup\$ It's not got very much gain. Lower R1 to 27k or even 2k7 as a first move. \$\endgroup\$ Mar 12, 2017 at 22:41
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    \$\begingroup\$ @Mascolini When you happen to be at you computer again, please post the screen-shot. \$\endgroup\$ Mar 12, 2017 at 22:42
  • \$\begingroup\$ You don't appear to have a voltage feed for the Electret. Just Google some schematics: qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/… \$\endgroup\$ Mar 12, 2017 at 22:44

2 Answers 2

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In commodity PC hardware, the computer microphone input has a pullup resistor to some positive voltage. A typical implementation is a 2K resistor going from the input to a +5V supply. The current through this resistor powers up a one-transistor FET amplifier that is built-in to the 'computer microphone'.

If your computer doesn't have the pullup (some Macs don't, if I recall correctly) then you will get no sound. Many good computer microphones have been thrown away because they don't make sound in incompatible devices!

As noted in the other answers, one solution is to redesign the preamp. Another solution would be to use a different type of microphone. In either case, the circuit will benefit from some additional work.

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  • \$\begingroup\$ I wasn't aware that electret microphones required power to work, nor that microphone jacks supplied 5V, I will redesign the circuit accordingly. \$\endgroup\$ Mar 12, 2017 at 23:19
  • \$\begingroup\$ Not all electret microphones are the same. There are several types and they have different bias requirements. \$\endgroup\$ Mar 13, 2017 at 0:53
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That cannot work.

You have a couple of things wrong:

  1. The electret microphone needs a power source. You have it connected to an input of the opamp - no power to be had there.

  2. You have the ground of the microphone connected to a voltage divider built of really high value resistors. Even if you had the microphone + connected to power, it still couldn't work because almost no current can flow through the ground connection of the microphone.


The rest looks really funky, too. You seem to be trying to build some kind of differential amplifier.

Stop. Search the web for a simple electret microphone amplifier circuit. There's about a million out there. Find one. Build it. See how it works. Compare it to what you came up with. See where the differences are.

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