Using iChat on a new MacBook Pro (a worthy replacement for my Pismo) to see some friends, we found out that the built in mic of the Laptop isn’t usable if you intent to move your mouth more then 10 cm away from the screen. So I remembered an old mono headset somewhere in the gizmo collection. I found it and found out – it wouldn’t work. After opening the mic cover and replacing it with one from a broken camera it was still not working – but as I was soldering it myself I thought that I may have destroyed it.

Today I bought myself a brand new headset attached it to the mic port and – guess what – found out it wouldn’t work. I tryed connecting the microphone directly to my stereo and it stayed quiet. Eventually I ended up opening the volume control of the headset and measured that everything was connected nicely (though stereo channel where interchanged). I could even measure a short-time connection between ground and signal of the microphone to disclose a condenser microphone there (what explains why it wouldn’t work with my stereo).

Now I got curious. Could it be that the MacBook Pro does not have a build in mic amp? And as it turned out the headset would work fine with the on board sound card of my workstation. After reading some forum posts and asking a friend I found out that there really is no such amp in newer Powerbooks. As Pismo had the option to  enable the amp even from Linux I didn’t even think of the possibility. 

Since I couldn’t return the headset to the store after opening it up I could ether buy a USB sound stick or try to get an external mic pre amp. Sven pointed me to a site (german) with an easy to build amplifier for condenser microphones and so I had to power up my soldering iron. 

Here are some pictures (Picture quality will get better again when I have a new camera ;-) ) of the working device. I used a 1.5 µF electrolytic capacitor as it was the nearest I found to 4.7 µF and it just worked fine.

As you can see the circuit is not bigger then the connector itself.

The only parts needed apart from the jack and some wires are a  2.2 kOhm resistor an the above mentioned condenser. I am also using one AA battery whilch will hopefully hold quiet some time.

You could say the MacBook Pro was giving me some geeky fun time. I guess that was what Apples engineers had in mind when they decided to delegate the selcetion of a mic pre amp to the user.