I have this electret microphone: http://www.farnell.com/datasheets/1505849.pdf

And I've put it onto a 3.5mm TRRS (4 pole) jack to go into the iMac headphone jack. For the iMac to recognise/accept the mic it needs to be wired with a 10k resistor in parallel and speakers must be 'faked' bz using 33ohm resistors for left/right lines.

It works well but the signal is weak. How can I amplify the signal just a little bit? This is a dirty prototype project and it's not about quality but just about the concept so the easier/quicker/the less parts involved, the better.

I think there is 2V coming out of the headphone jack for the mic but I'm not sure. Is it possible to amplify the mic without using an external battery/energy source?

I tried this circuit but there was just no signal anymore?

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    \$\begingroup\$ The circuit that you tried won't work because it does not supply a DC bias to the microphone. A dynamic mic needs no bias, but an electret "microphone" actually is a package containing a transducer and a FET preamp. The preamp will not operate without power. \$\endgroup\$ Commented Aug 28, 2015 at 17:54
  • \$\begingroup\$ I'm surprised this didn't get any serious answers... and you've probably solved your problem by now. My typical setup is a two-stage NE5532 10x amplifier (100x gain overall). The keywords anyone wants to search for is "preamplifier" (in conjunction with electret etc.) For some reason that's how it's usually called. There are a lot more pretentious chips, designs etc., e.g. ti.com/lit/ug/tidu765/tidu765.pdf \$\endgroup\$ Commented Sep 29, 2015 at 7:29

1 Answer 1


That particular electret has a pretty low sensitivity. You might simplify your life by using a mic with a higher sensitivity, or better yet, one with adjustable gain built in. This mic from Knowles has adjustable gain. This app note has a pretty good explanation of how to convert a three wire mic into a 2 wire mic (with Vdd and data sharing the same line).

  • \$\begingroup\$ Thanks but I'd really like to just amplify the signal instead of using other microphones. \$\endgroup\$ Commented Jul 24, 2015 at 7:28

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