Elektrosluch is an open-source device for electromagnetic listening. It allows one to discover the sonic worlds of electromagnetic fields, surrounding our every step. At the end of this project you will have a working version of Elektrosluch, ready for your headphones to be plugged in. Consequently you will be able to listen to the electromagnetic fields of the various devices around you. My suggestions for starting out are to place the Elektrosluch near computers, tablets, cellphones, cameras, and CD players, to listen to the unique sounds of their electromagnetic fields.

 

In this tutorial, I’ve designed a version of Elektrosluch with the least amount of parts possible, open for future upgrades in one’s personal taste. Certain part values are variable and the options are described in the steps.

Elektrosluch Parts

All the parts you’ll need to create your own Elektrosluch. All photos by Jonas Gruska.

This tutorial assumes using a perfboard with at least 15 x 24 holes, and requires attention to spacing of the parts on the board. Please see the layout for exact coordinates of parts on the board if spacing or size is an issue. Also, pay close attention to the layout image and photos to see how to connect the parts between each other on the bottom side of the breadboard. Leftover leads from resistors/capacitors can be helpful in creating longer solder-bridge paths.

Elektrosluch DIY Schematic

STEPS

1. Solder in the inductors, L1 and L2. Make sure they are space far enough apart to create a perceptible stereophonic experience when listening. These inductors are the essential parts of the projects—basically very long loops of thin wire around a metallic core. They act as antennas for magnetic field and allow us to pick-up the electromagnetic fields.

Elektrosluch 2
2. Solder in the 2.2 µF capacitors, C1 and C2. These capacitors define the bottom cut-off frequency of the circuit. The higher the value – the more bass frequencies you will get. Since bass frequencies picked up by Elektrosluch are mostly 50/60 Hz mains (depending on your country), some people prefer to use lower values to get rid of those.

Elektrosluch 3 Elektrosluch 4

3. Solder in the 1 kΩ resistors, R1 and R2. These, together with R3 and R4 (390 kΩ) define the gain of the circuit. The topology used is called “inverting amplifier” and with provided values results in gain of -390. The minus represents that the signal is inverted to the original, but in this circuit that doesn’t really matter.

Elektrosluch 5 Elektrosluch 6

4. Solder in the 390 kΩ resistors, R3 and R4. As you can see in the picture, they are soldered “standing up” to save the space.Elektrosluch 7

5. Solder the socket for the integrated circuit (IC) we will be using. The ICs can be soldered directly, but I highly recommend putting in the socket, because it will allow you to replace the IC if you accidentally break it or want an upgrade. It also lowers the risk of damaging the IC during soldering. As you see, solder bridges have been made between the socket and resistors

Elektrosluch 8 Elektrosluch 9

6. Solder in the 2.2 µF capacitors, C3 and C4. These will, together with C1 and C2 define the amount of bass you will get from the circuit. Higher values will result in more bass and vice versa.

Elektrosluch 10 Elektrosluch 11

7. Solder in the 100 µF capacitors, C5 and C6. These will be part of the virtual ground circuit, which is necessary for operation with operational amplifier.

Elektrosluch 12 Elektrosluch 13

8. Solder in the 100 kΩ resistors, R5 and R6. These two resistors will be defining the virtual ground point. They act as a simple voltage divider, which in this case divides our 9V battery into three potentials: 0 V, 4.5 V and 9 V. For our IC this will become -4.5 V, 0 (virtual ground) and +4.5 V.

Elektrosluch 14 Elektrosluch 15

9. Solder in the headphone jack and wires. These will connect the output of the C4 and C5 to the headphone output. Left channel is blue and right channel is green.

Elektrosluch 17 Elektrosluch 18
10. Use a piece of wire to connect the positive voltage supply of the IC to the positive point in our virtual ground circuit at the bottom (C5/R5).

Elektrosluch 20

11. Now you can mount in the IC, OPA2134 into its socket. Feel free to experiment with other operational amplifiers. Opamps with the same pinout include the LME49720, TL072, OPA1662, NE5532 and others.)

Elektrosluch 21

12. Solder in the battery leads in a way that the negative lead is connected to C6/R6 and positive to C5/R5.

Elektrosluch 22

13. Double check all the connections on the bottom of the board.

Elektrosluch 24

14. Plug-in your battery, plug-in your headphones and start exploring! You can create a simple battery holder by using a piece of double-sided mounting tape underneath the battery.

Elektrosluch 25

Taking it further

This device doesn’t have a volume control—you can add it if you like by placing a dual logarithmic potentiometer before the headphone jack.

This device doesn’t have a on/off switch—if you want one, place it in between the positive connection from the battery and the rest of the circuit.

The version presented here is bare-bones, but it will work great for starting the exploration of electromagnetics. Feel free to experiment with different gain configurations, capacitors and op-amps. There is not much in this design that can go wrong. Feel free to share you creations with us through zvukolom [at] zvukolom.org.

Jonas Gruska

Jonas Gruska

Born in Czechoslovakia. Studied at Institute of Sonology in The Hague (Netherlands) and at Music Academy in Cracow (Poland). His main focus are chaotic rhythms, exploration of psychoacoustic properties of sound and field recording. He has created several site-specific sound installations, based on resonant properties of spaces and materials. Gave workshops on sonification, field recording, printed circuit board design, and programming for artists. He is also a developer of musical instruments, artistic software and hardware.


  • aghost21

    That OPA is such the wrong opamp for this kind of build. It’s meant for high end audio applications such as preamps, and filters. Its low end is even enhanced. For the love of god just slap a TL072 or TL082 in there, and save a few bucks in the process. On top of that the 72 and 82 are going to sound a lot crisper and clearer than the OPA as their slew rates are much higher. I’m all for experimentation, but give people a concise cheap base model to start from. It’s like slapping a Hemi in a Geo Metro and telling people to build off of it.

    • mrkva

      I actually tried TL072 and it didn’t sound as good as OPA2134. Might be a matter of taste. My current favorite for this circuit is OPA1662, but it doesn’t come in DIL package.

      • aghost21

        Those OPA amps are more than likely smoothing out the signal significantly due to their slew rate and noise rejection. Add a simple variable low pass filter before the opamp to give yourself a ton of control over the signal coming in, and that TL072 will sound like magic.

        • mrkva

          I am really not sure what you’re talking about. OPA2134 has higher slew rate (20 V/us) then TL072 (13 V/us) as well as lower noise (8 vs 18 nV/sqrt(Hz)). It also sounds better from my experience. Am I missing something?

          • aghost21

            Don’t worry about it, it’s not important. Everybody has their preference. You found what you like and there is nothing wrong with that.

          • mrkva

            Yeah! That is also a reason why I suggest using the socket in the project – one can try different opamps with the same pinout and see what sounds best to them.
            Have a nice day! Glad we sorted it out :)

          • Ayab

            I would really like to build this project and have some parts but am not sure what value of inductor is best to get hold of. Any advice will be appreciated. Great project by the way thank you : )

        • Ayab

          Hi aghost21
          I have a spare TL072 can you pls indicate how you would recommend adding a simple variable low pass filter before the op amp (simple pic of a schematic) would be much appreciated. Is the filter necessary? – as in I might prefer deciding on what to filter after recording for more flexibility.

          • aghost21

            You can add something along these lines into the output path of the opamp. Add this to each channel and control them with a dual gang pot. And no the filter isn’t necessary, but it can help to control high frequencies, as well as help dial in certain freq’s.
            As for the inductor the instructions say a 22mH inductor.

          • Ayab

            Thanks so much aghost21 – that looks like an elegant filter which I think I will add. Also thanks for the info on the inductor. Looking forward to entering the electromagnetic sound world!

  • jrf

    another alternative is to simply buy a coil pick up & plug it in to your recorder (if you have one) or even a mobile phone with any free recording app. If you get an unlimited one (I have them or in some countries you can get them – here in the EU they mostly have limiters in) you will also get a wider range of frequencies.

  • This project looks like a lot of fun! Thank you for sharing. I’ve started gathering parts so I can build it. I have a question though.

    I found the schematics for the different versions of the Elektrosluch on LOM Instruments’s github page ( https://github.com/LOM-instruments ), and I see the biggest difference between the DIY version and others is the lack of a 47pF capacitor in series with the 390k resistors (R3 and R4 on the DIY schematic.) I’m curious what effect this has, or what the purpose of those capacitors is? It seems like it would be easy enough for me to add them in.

    • mrkva

      They offer high-frequency filtering to protect from RFI frequencies. However, in effort to make the design easier, I decided to not include them.

      • Thanks!

      • Michael Anton

        This wouldn’t protect just from RFI, as the -3dB point is at 8682 Hz, which is pretty low. The high frequencies will be much more present without the 47pF capacitor. The GBW of the specified amplifier is 8 MHz, so with a gain of 390, the amplifier will start to roll off all on its own at just over 20 kHz, so it is already reasonably safe from RFI.

        • mrkva

          You’re right, however in my personal experience that cap still really helps with RFI (even though in theory the diminished bandwidth due to high gain should too).
          On the other hand, this device _should_ pickup all kinds of EM noise, so maybe RFI should stay :)

  • djones

    What would the polarity of caps be if using all electrolytic capacitors?

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    • mrkva

      Plus towards the input (the coils)

  • Sympou

    I just made it (with the TL072 chip) and it sounds great ! I’m very excited to hear the usualy unhearable. I think I’m going to make some experiments with this circuit. thank you M. gruska !!

    • mrkva

      Would love to see a pic! Hit me up :) jonasgruska (at) gmail (dot) com

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  • Timothy Gilman

    After listening to that bus, I wonder if there is some way I could throw a YM3812 (or YM2413) into the mix…

  • Heidi

    Can I use a 27 mH inductor? I can’t find a 22 mH inductor like that but I did get some 27 mH ones.

    • mrkva

      Try it out. It will have less high frequencies, but should work.

      • João Silva

        I could only get a 60mH. What do you think?

        • mrkva

          That seems a bit too much. Try checking other electronic part suppliers.

  • Dan Stork

    I am a bit confused when it comes to C5 and C6 – I am struggling to figure out which way to solder them as in polarity wise. It appears on yours as if the negative of C6 is farther away from the IC and the negative of C5 is closest to the IC – Is this correct?

    • mrkva

      I recommend checking the schematic for this, the polarity is marked there.

  • Dan Stork

    Hi, I have finished mine and it worked for a second or two. I unplugged it to change to different headphones and now no matter what I plug into it it simply crackles occasionally and the IC heats up. Any ideas – as you can see I am pretty beginer

  • Got it built! Well, the circuit at least. I still plan to case it up and add a volume pot but for now I made a quick video. https://www.youtube.com/watch?v=KAiytsMVd18 I’ll take photos once it’s completely finished. Thanks for a very cool project!

  • João Silva

    Can I use different inductors?

    • mrkva

      You can try, but I had most success with 10mH – 22mH values.

  • Mohamed A. M. Mostafa

    I can’t seem to get the inductors at any of my country’s electronic supply stores. is there a solution? can i use a diy coil? do you a device i can salvage them from?

  • Bela Matahari

    Hi! I’m the first timer of doing electronic configuration. I’ve been trying about 4-5 times, but the sounds just won’t come out. Could you please give me a clue if I did something wrong?

  • Ruthsarian

    I’ve got this working on a breadboard and I plan on putting it on perfboard and into a case once I’m happy with the setup. I want to add a few extra things like an on/off switch, volume control, and experiment with a variable low-pass filter like aghost21 suggests.

    I’d also like to add a speaker that is used when headphones are not plugged in. I tried hooking up a small 8 ohm 1/4 watt speaker and it works, but I find the volume is too low to my liking. How could I increase the volume? Would I replace the 390k resistors with something larger (like 1M)? or drop the 1k resistors to something lower?

    I was also thinking of putting 1/8 mono female plugs in place of the inductors, then attach inductors to 1/8 mono male plugs. The idea being to 1) make the inductors easily swappable so I can try different values and 2) be able to extend out the inductors away from the board either a few mm attaching an inductor right to the plug, or maybe even use a couple feet of wire so I can have greater control over how the inductors are positioned. Would that work or would all the extra copper create problems?