Phantom powered microphones need some voltage to work. The P48 standard defines how to feed these mics with 48volt through the XLR connector. Of course, I could buy one of the professional fiels Shure FP23 or Sound Devices Mic Pre, but I didn't want to spend that money. There are some other alternatives like the Juicedlink JL-CX231 or the Beacktek DXA-2T, but also quite a spend.
The other opion was to build an adapter myself.
After some research about the P48 standard and some DIY, I decided to put together four circuits I found:
- The Low Noise Balanced Microphone Preamp by Phil Allison
- The 48V Phantom Feed Supply for Microphones by Rod Elliott.
- The DC-DC step up 9v to 48v step-up converter by Thomas Schaerer.
- The MAX1044 / ICL7660 Negative Voltage Converter (see application notes), needed to get the -9v for the preamp circuit.
The result is a transformerless cheap 9v portable single mic preamplifier. It is important to remark that it is transformerless. I looked for the proper audio transformers (Jensen, etc.) in order to insulate the mic and the camera, but the prices are too high for this project.
This is my arrangement of the component in standard prototyping boards:
This is a picture of the circuits in a standard box: