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Electret microphone into iMac-3.5mm TRRS headphone jack amplification

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kyson lin
Electret microphone into iMac-3.5mm TRRS headphone jack amplification
on Mar 14, 2017 at 3:09:11 am

Hello, everyone in here. I'm very happy to be here.

I have this electret microphone:

Then 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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Richard Crowley
Re: Electret microphone into iMac-3.5mm TRRS headphone jack amplification
on Mar 14, 2017 at 4:34:28 am

The electret mic capsule requires that DC voltage to operate. Your circuit has capacitor C1 which isolates the microphone from the DC voltage it requires.

You could start by removing C1 and connect the mic capsule directly to the base and R1. However, since there are so many unknowns here, the value of 470K ohms for R1 may very possibly be too high. It may require a much lower resistance, perhaps more like 47K or even lower to match the impedance of the mic capsule while properly biasing Q1 for linear operation.

You may need a more sophisticated version of this kind of circuit...

But that circuit assumes a separate power supply. It might be possible to modify the circuit to use the "plug-in power" from the camera, but it may be beyond the scope of your "dirty prototype" limits.

Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

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