Weekend Project: Listen to Weird Sounds from Electromagnetic Fields

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.

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.

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.

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.

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

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.

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.

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.

Solder in the headphone jack and wires. These will connect the output of the C3 and C4 to the headphone output. Left channel is blue and right channel is green.

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).

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.)

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

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

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.

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.