Convert your obsolete MBox 3 into just a dual mic preamp

Avid haven’t updated the drivers in years, and the MBox 3 is really glitchy on Windows 10. So why not cut out the digital entirely and just make use of its preamps?

You could surely do this with any other interface, too, but the MBox 3 is what I have.

Avid Mbox 3 3rd Gen USB 2.0 Audio/Midi Interface | PSSL ProSound and Stage  Lighting

Remove the feet to access the first of the screws to be removed – there are many more inside. You often don’t need to remove as many as it might appear though – when you get to the stage pictured here, you only need to remove the nuts/screws circled.

On the back panel, however, you need to remove every screw and nut.

Wire it up like this, and snip two traces in each of the locations circled in green. This bypasses the audio codec IC (centre), and sends the (balanced) preamp output straight to what was the codec’s output circuitry. Ultimately it comes out of the “monitor” outputs. Levels are appropriate enough that everything works well.

And, you should defeat the volume pot as it’s now unnecessary, and is prone to crackling and adds signal path length / potential noise. On its connector, J13, counting from the left, short pins 1&2, and 6&7 together.

Please forgive my absolutely terrible soldering job, I’d had enough and just wanted it finished. And this is real close-up.

I experimented briefly with cutting out even more of the audio circuitry / opamps, but didn’t have any luck like what the pictured configuration achieved, which by the way was as close to perfect performance as I’m able to measure. Further investigation could definitely be done and results could probably be had if I decided to spend more time on it, but I’m perfectly happy with the project as-is – an all-analog dual mic preamp with phantom power and pad function, for no cost and saving perfectly good hardware from the landfill despite it being doomed by a simple software incompatibility.