Plasma speaker with a ~10kV arc (Video Below)! I made a DIY plasma speaker using a Flyback Transformer, 6x1.5V batteries and an Arduino! Below is a video of my plasma speaker playing the Star Wars Theme.

https://youtu.be/JnshBPd_8rM

(It works better with a shorter arc!)

I made a Triangle Wave generator using Op-Amps and then used a IRF840 MOSFET to control the current going through the primary coil of the Flyback Transformer. The Flyback Transformer is easily obtained from old CRT Televisions that use the transformer to generate high voltage. The schematic of my setup is shown below.

(The IRF840 is labelled in the schematic as IRFP250N instead. Either one would work.)

The circuit on the left is the Triangle Wave generator made from TL082 Op Amps, which serve as the "driver IC" for the MOSFET. I tried running the circuit, but soon faced the problem of MOSFETS exploding violently, even with appropriate heatsinking.

To circumvent the problem, I dropped the duty cycle of the gate signal to around 5%. This would strain the MOSFET less. To do this, I used an Arduino to pull the the non-inverting input of the comparator op-amp to 0, 95% of the time. This is done using the Arduino's built in PWM code. When the Arduino input is high, the signal to the MOSFET will be 0. When the Arduino input is low, the signal to the MOSFET will be the 50kHz square wave produced by the op-amp oscillator.

By varying the frequency of the PWM using some Arduino code, the 50kHz signal can be toggled on and off at the sound frequency, thus producing sound in the arc. As a result, a monophonic melody can be produced.