Jan 15, 2010

Portable P48 microphone preamplifier

Once every while, I like to have a look at second hand shops searching for any nice deal. In one of these visitsI bought a Sennheiser MKH-416 P48 professional shot gun microphone for 275€. But then I had the problem of how to interface it to my videocamera.
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 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:


  1. hey mate! I'm really curious about this build. do you have a sample audio/video of this? :D

    1. Hi!
      I gave the thing away about two years ago, so I don't have it anymore. I'll have a look on my backups to see if I saved some sample recording to share.

    2. "Hi,

      My name is James McCanna. I am the guy that David generously sent the preamp to in the United States. It is really a cool device and works well.

      I have recorded a small audio clip recording my acoustic guitar at 16-bit/44.1kHz. It is a completely clean recording. The preamp is very quiet and makes my microphone sound terrific. The link is here: http://www.pcrecording.com/GibsonAcousticMono.wav

      The microphone used is one of my own design using copper pipe. It is a phantom-powered large-diaphragm microphone using modified Schoep's circuit (Alice circuit by Scott Helmke). It sounds great too. The link is here:



      James McCanna"