I made a low-cost (about $10 in parts) microphone preamp for use with electret microphones. It’s basically the Texas Instruments reference design here
It’s extremely clean and high fidelity, running on a 9v battery for minimum noise. I designed it to fit on the side of such a battery so it’s as tiny as possible.
The specified electret microphones are 6mm with a 68dB s/n ratio and a -35dB sensitivity, which is rather great for the low price.
Using 1.5m Mogami 2330 wire, I connected up a couple of units and hooked them up to my oscilloscope. I then played a sine wave out of my studio monitors and checked the output with the mics at different distances and angles:
So yeah, it works pretty nicely! Especially good for doing some binaural stuff into Norns, which was my primary reason for doing this.
Here’s the github page with all the files:
And here’s the Mouser cart (I think…)
The microphone-side cable should be as low capacitance as possible, and ideally extremely short. Longer (>1m) cables that are not low capacitance may cause instability in the amplifier. The cable from the output can be fairly long without issue.
Added the “Tiny Mic Pre” version, found in the subfolder with the same name. In theory, this will sound better than the previous version as there is no distance between the microphone capsule and the circuitry. The microphone cable used should be have relatively heavy-gauge conductors in order to minimise the effects of having the battery far from the circuitry. 26 or 24AWG should be fine, two or three conductors and a shield for the ground.
It’s designed to fit inside a 6mm inside diameter bit of brass/steel tubing.
I’m adding the zip file containing 3D-printable .stl/.obj files for a really elegant housing for the board and battery, as designed by the wonderful @infinitedigits
Definitely beats my blutak system anyway!