I have created a system to plug my studio mic (MXL 990) into my MacBook's 3.5mm headphone jack that consists of the following system:
Mic -> AC Power supply for the mic -> 3-Prong microphone cable to 6mm headphone jack transformer -> 6mm to 3.5mm converter.
The system, however, doesn't work. I have tried diagnosing the problem myself with the following:

  • Using a different mic
  • Skipping the transformer in the line
  • Skipping the AC Power supply in the line
  • Hooking up to a different mac, and directly to a speaker.
  • Checking the output voltage of the AC power supply

Mic -> 3-prong mic cable (1)

3-prong mic cable (1) -> AC Power supply to mic -> 3-prong mic calbe (2)

3-prong mic Cable (2) -> Transformer -> 6mm jack -> 3.5mm jack -> Computer

  • \$\begingroup\$ Your 3.5mm jack only seems to have 3 connections. Have you seen this? apple.stackexchange.com/questions/99304/… \$\endgroup\$ – Wesley Lee Sep 26 '16 at 1:41
  • \$\begingroup\$ It should only need three connections, as the microphone cable leading to it also has three connections @WesleyLee \$\endgroup\$ – ALX Sep 26 '16 at 1:45
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    \$\begingroup\$ Technically it could only need two connections, what I mean is that possibly the Mac wont even recognize it as a mic without the 4th connection. \$\endgroup\$ – Wesley Lee Sep 26 '16 at 1:46
  • \$\begingroup\$ You have a point, but it didn't register when I plugged it into my speaker either @WesleyLee \$\endgroup\$ – ALX Sep 26 '16 at 1:57
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    \$\begingroup\$ So does the mic work with anything, or are you just assuming it works? \$\endgroup\$ – Bruce Abbott Sep 26 '16 at 6:12

You have a couple issues going on here.

First of all, you are not connecting to the mic input of your computer. That jack is a TRRS jack with the mic input being on the second ring. Your adapter is TRS so you're basically connecting a headphone output to your microphone.

That transformer is doing you no good either. It's designed to bring the impedance of your microphone up so you can plug into Hi-Z amplifiers like a guitar amp for example. This is not what you want here since the impedance will be too high for the input you're using.

This is sort of a crude way to record a microphone, but you can at least get some sound out of it if you connect to the second ring of a TRRS plug, and make sure to adjust your sound input level in your Mac's system preferences. Be sure to choose the correct input as well. Your phantom power situation looks fine.

I have done quick and dirty things like this in a pinch before. I actually got away with plugging a guitar directly thru an adapter into my Macbook and got some sound out of it (plus a ton of noise of course since it's Hi-Z). That was back when the Macbook Pro had a separate line input so I didn't need to deal with the TRRS thing. The key is to hit the right input and turn your input volume up enough. It's not pretty or proper but you can at least hear something.

If you wanted to do this a bit more professionally and cleanly, you should get a proper mic preamp and audio interface. Then you could do away with the clunky phantom power supply. The situation described above is only really okay for non-critical stuff like playing along to songs in your dorm room etc.

Hope this helps!


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