Telephone handset mic

I was asked if I could build a mic from an old phone handset and found that challenge interesting. I didn't work before with a balanced XLR, neither with a Phantom power. A bit of research led my to this brilliant page created by Mike Thornton "A Lo-Fi Mic - Studio Hack" so I just followed what he designed. The basic idea is to use a central tapped transformer to convert unbalanced input into a balanced output while injecting a power. I also had to create a little converter to take back XLR into a regular 1/4 input so I can test my build with a guitar amp. 12V battery works as a power supply

One gotcha was to find a 5 pin audio transformer with a central tap. I bough a set on Aliexpress but they turned to have a central tap just glued and not connected anywhere. Finally I just soldered two transformers in series, luckily those are small enough. It took me a while to find a real central tapped once at a reasonable price for the next builds. 

The final product went very well and sounds fantastic. The mouthpiece carbon mic gives a really rough broken sound when the earpiece dynamic mic sounds smooth. This should be great for someone looking for a vintage telephone style tone when recording.

I built two of those so far, one was sold already so I'm starting the third one.