DIY Priezor — Ambient EMF Antenna Microphone

Note: If you are just looking for the step by step instructions, scroll down. I also realized there was an issue with the Tinkercad link. I’ve fixed it and added a backup Dropbox link.

LOM Audio is a company that makes some amazing and affordable microphones for field recordists and sound designers. One of the coolest things they make is the Priezor.

Priezor (Image from store.lom.audio)

It utilizes a coil of copper wire to record magnetic fields generated by electrical equipment. I’ve always wanted one but LOM has been sold out for quite some time. I decided to try my hand and making one myself.

LOM was considerate enough to open source the project. The way they built it was by laser cutting acrylic, assembling it with nylon screws and standoffs, and winding the copper wire around the hoop. Then, the ends of the wire are soldered to the two signal conductors of an XLR cable.

Here is a video they released showing how it should be assembled:

LOM has even built a robot to automatically wind the coil!

You can find the DXF files for printing on a laser cutting machine on their github (https://github.com/LOM-instruments/Priezor). Which is great if you have access to a Laser Cutter!

Unfortunately, I don’t, but I did recently purchase myself a 3D Printer. DXF files are not supported in 3D printing slicers but the design is simple enough that I decided to create a 3D model version.

I decided to make my model in TinkerCad. It is a free CAD style tool developed by Autodesk. The nice thing about my design is that it is only 2 pieces!

The LOM design uses about 7 pieces and sandwiches them together. My design includes the standoffs as part of the antennas hoop. The handle itself is also one piece, with a tunnel cut through the middle to allow the cable to thread through.

Here are a few images from TinkerCad:

Priezor 3D Model on TinkerCad

Here is a link to the model itself if you’d like to print one: https://www.tinkercad.com/things/2R6ptaSiUqw-priezorantenna

EDIT: Someone mentioned the tinkercad link was broken. If you have trouble, you can download the stl from my dropbox: https://www.dropbox.com/s/5kyze06xdrpfmq6/PriezorAntenna.stl?dl=0

There are a few things I learned in the build process that I would like to share. Firstly, I’m not 100% sure if the size of the antenna is the same as an OG priezor. It’s pretty close as it feels good in my hand and sounds nice but it might be a smidge smaller. If anything this will change the resonant frequency of the antenna but shouldn’t affect frequency response too drastically.

Second, I should have done a better job of sanding and filing away rough edges. Due to a few bits sticking out here and there, the copper wire would catch every so often and risk snapping. This slowed down my winding which was already slow as I was doing it by hand.

Third, I needed a better solution for keeping track of how many turns of copper wire I used. A turn is one full rotation of wire around the hoop. The LOM steps suggest 333 turns. I think I got somewhere around there but lost count around 160ish.

Fourth, this isn’t the most efficient method of making this mic. If you have access to a laser cutter it will be degrees faster as the cutting process takes less time than 3d printing.

Unfortunately, I didn’t take a lot of photos of the build process but I can summarize the steps below.

Materials and Tools

1. PLA Filament and a 3D Printer with a print bed of at least 200mm x 200mm
2. Around 14 grams of .15mm enameled copper wire
3. 3x M3 x 20mm screws with associated nuts
4. Microphone cable (around 1.5m)
5. Male XLR Connector
6. Soldering Gun and Solder
7. Hot Glue and Gun

Step by Step

1. Download the model in your file of choice (I use STL)
2. Import the model into your slicing software and export a gcode file.
3. Prep your 3d printer and print the model. My print took about 4.5 hours on an Ender 5 Pro.
4. Once the print is complete, let the machine cool and remove it from the bed. Post-process the print by lightly sanding and cutting away any sharp or jagged edges, especially in the screw holes and the trough for the wire.
5. Once the print has been cleaned up, you can now start coiling the wire. Take your wire and measure out a length about as long as the handle. Leave this hanging off the edge to act as one of your signal connectors. Make sure this length of wire stays near the screw holes for the handle at all times.
6. Rotate the hoop, threading wire into the trough as you go. Once you complete a rotation, count that rotation and keep track of it somehow. Repeat this step about 332 times.
7. Once you have completed your 333-ish turns, you should see what looks like a solid wall of copper in the trough. Gaps here and there are fine. At this point, you’ve essentially built yourself a guitar pickup.
8. Now measure out a length from the end of the wire about the same length as the handle. This is for your second signal conductor.
9. At this point, I would recommend hot gluing the wire down right next to where the handle screws go. You don’t want the wire to be loose as you connect it. Don’t apply too much or the handle wont be able to fit snug against the hoop.
10. Once your glue dries, thread your microphone cable through the handle and solder each of two copper wires to the positive and negative lead on your cable. We don’t use the ground on this build. NOTE: I would recommend using some electric tape and/or shrink wrap once you have attached the cable and the solder cools. This will protect the connection and make it a touch more secure.
11. Now, slide the handle up into position to line up with the screw holes on the hoop. Thread three M3 screws through all the way to the other side. This may be a bit slow as the holes are a bit snug. Then connect the nuts and tighten. Don’t overtighten or you can snap parts of the print.
12. Once the handle is fully connected, solder the XLR connector to your cable. Remember, we are only utilizing positive and negative leads. No ground on this build. You can connect the ground if you want the shielding of the mic cable to be used here but it’s not necessary to function.
13. Plug it in to a preamp and test it out! Do be careful with your gain at first as some EMF recordings can exhibit incredibly high amplitudes.

Hopefully this helps you build your own! Don’t hesitate to hit me up if you have any questions. You can reach me on twitter: https://twitter.com/jeffbrice

Here are a few pictures of my finished build!

Left -Final Priezor (Black) and Baby Priezor (White). Right — Perspective on cable tunnel

Left — Priezor size comparison relative to hand. Right — Perspective of the Copper Wind