Monday, March 9, 2009

The Plasma Speaker

Are you tired of those old black speakers that only just make sounds? Maybe sound reactive lights are just not enough to impress you?

How about a Plasma Speaker?

A plasma speaker is a device that generates an high voltage electrical arc that makes purple light and music! Without any speakers or any moving parts!

Sounds too good to be true?
Well, you're wrong, the high voltage arc really does sing by vibrating in the air. (Of course, you will need to give the device musical audio for it to work.)
And just leave this instructable if you still don't believe me...

And this is something I always wanted to build - I have been dreaming to build one for about 6 months, until Kiteman has greatly boosted my encouragement to build one. (Thanks Kiteman)

The video of my plasma speaker - early prototype.

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step 1The dangers you must know...

A plasma speaker is no toy...

Health Hazard
Unlike the ordinary speakers, the plasma speaker are dangerous high voltage device, do NOT attempt to build this device unless you know what you are doing... And do NOT even attempt to build one if you have heart problems or weak heart or wearing a pacemaker, because one little shock from this thing can put you out...
I am not responsible for any injuries or deaths caused by this device.

Why should you know all of this? it is because you can ONLY live once, and no more...
If you don't think that you shouldn't build one, just watch movies of it working instead, much better than risking your life to build and operate one.
If you think you are okay to build one without killing your self, then move on to the next step.

Hazard to Electronics
Since the plasma speaker generates high voltages, there is a chance there will be high voltage spikes on the low voltage side of the device, which can get onto the audio line and damage (or destroy) the player. They are some safety features to prevent the spikes damaging the player, but they can fail... So I am not responsible if your player gets damaged, and use cheap players like CD players, if you're rich, you can use expensive players if you want. :-)
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step 2Schematics

I got the idea from scopeboy's website on his flyback driver section, but the schematic was quite complex and buying four MOSFET's is a little too expensive to me...

So I simplified the design to using one MOSFET, and it works quite well too!
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step 3So, how does it actually work!?!?!?

Okay, you must be very curious how the plasma speaker works...

Note: This information is technical, skip this step if you don't understand...

The TL494 acts like an oscillator and a modulator, it generates a high frequency (5KHz to 45KHz) to drive the flyback transformer to make high voltage arcs. Then when you give it audio, the TL494 modulates the audio frequency into the main high frequency. Now the flyback transformer is being driven by the high frequency and the audio frequency, and when the arc is produced, the arc vibrates the air with both the audio and high frequency creating sounds.
If you tune up the 22K potentiometer, the high frequency increases, when it goes higher than 20KHz, we cannot hear it, but only the audio frequency...

I hope you can kinda understand this..
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step 4What you will need...

You will need quite a lot of stuff to make the plasma speaker...

  • TL494 chip (Datasheet for TL494)
  • 200uF (or 220uF) electrolytic capacitor
  • 47nF 250v (or similar voltage ratings) capacitor
  • 100nF capacitor
  • 10nF capacitor
  • 2.2K resistor
  • 10 ohm resistor
  • UF4007 diode (or other fast diode)
  • 10K potentiometer (same thing as a variable resistor)
  • 22K potentiometer (same thing as a variable resistor)
  • Audio jack
  • Wires
  • IRF540 MOSFET (or other ones with similar ratings) (also get a few spare ones, if one of them blows)
  • Large heatsink
  • Flyback transformer (you can get one from an old CRT.)
  • 12v power source for TL494 oscillator (I used a 9v battery)
  • 12v to 40v power source for the flyback transformer
  • Bread board (for testing)
  • Veroboard

I bought most of my electronic parts from Farnell.

  • Soldering iron
  • Wire strippers
  • Wire cutters
  • Pliers
  • Helping hands
  • Hot glue gun

  • Good with a soldering iron.
  • Can read schematics.
  • Know what you are doing when you are dealing with high voltage.
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step 5Build the prototype on the bread board

Do what the title says... Build the circuit on the bread board!

Why on a bread board and not build it directly onto the veroboard?

Well, it is a very good idea to build the prototype on the bread board before you solder the components onto the veroboard because...
  • You will get a better idea on how to build a 'real' one on the veroboard.
  • You can make sure all the components are working fine, if not, you can replace it easily.
  • You can modify or tweet the circuit a bit to give the plasma speaker a better performance.

I built my circuit using my simplified schematic on the bread board that is connected to the "Electronic Lab" kit that I got a long time ago.

To connect the flyback transformer to the circuit, wind 5 or more turns of thick solid-core wire on the ferrite core. That will be your primary coil.
out:{ top: 0.37333333333333335, left: 0.508, width: 0.142, height: 0.35733333333333334, text:"MOSFET with a massive heatsink." }

step 6Test the prototype

After you had built it, go ahead and test it!
If it does not work, don't get all frustrated or anything like that, go back and check your circuit closely, make sure there are no missing connections, and check the components are properly connected to the circuit...

Mine works quite well, unfortunately, the MOSFET is wasting large amounts of energy into heat, so it is blazing hot... I have to make the heat sink bigger to try keep it cool longer. But it still goes blazing hot after three minutes of continuous operation.
Oh well, that is my efficient design so far...

If yours working well with out very much problem, thats great!
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step 7Build the circuit

After you have tested to make sure everything is working, start building the prototype onto the veroboard.

If you notice in the pictures, I use an 16 pin socket for the TL494, it is really good idea to use sockets for the IC' s because you won't risk heat damage from soldering, and if the IC fails, you can easily replace it instead of desoldering it and solder another one in..
I also added an LED indicator, that is a good idea to add that on too, so you know whether the circuit is on or off. The LED indicator is connected to the TL494's power supply line.

After you had done soldering, make sure you made nice shiny solder joints and they are no solder bridges. If you think it is all good enough, add some dab of hot glue onto the loose components and wires for strain relief.

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step 8Final test

Okay, you are very close...
Test your plasma speaker to make sure if it is working or not.

If its working, let out a sigh of relive that you did it!

If its not working, don't overreact of frustrated, (I know it is very frustrating when something does not work).
A few things can go wrong with this circuit, here is a list of some problems...
  • Solder bridge - That is the most common problem in soldering.
  • Some connections missed out - Also another common problem...
  • Damaged components
Try find and fix the problem, there is no point giving up - unless you are really lazy to do so...

After you got your plasma speaker working, it is a good idea to the circuit into a project box. I will protect the electronics from being damaged from foreign objects and protects people from an electrical shock.
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step 9Enjoy and impress your friends!

Well, there is the instructions to make your own Plasma Speaker! Go ahead and pump in your favorite music then listen and watch the arc dance with the music and admire what you had built...

Then show it to your friends and family, I can guarantee you they will be greatly impressed.

When my Dad first saw my plasma speaker in operation, his first words about it are: "What the f... Tha... Thats impossible." He is wrong, nothing is impossible... Nothing.

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step 10How to use the plasma speaker

Here is how you can control the plasma speaker with the two potentiometers.

The 10K potentiometer is used to change the TL494's internal oscillator frequency - from 5KHz to 50KHz. If you want to play music on the arc, tune the frequency up until you don't hear it and play the music. Note: The 10K potentiometer does NOT affect the input audio (music).

I am not too sure what the 22K potentiometer's job is, but it seems to change the volume of the audio, fiddle with the 22K potentiometer until you can hear the music loudly. Note: Making the music louder will shorten the length of the arc.
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step 11Interesting discharges...

Just a little story I like to tell you about...

While I was testing (well, playing) my plasma speaker, the 12v battery is going flat and the arcs are becoming unimpressively short. So I replaced the battery with my lab PSU I modified from an ATX PSU and put an 22,000uF capacitor in parallel with its 12v output and ground.
The 22,000uF capacitor is used to adsorb any high voltage spikes that may appear on the line.

When I connect the PSU's power to the plasma speaker and turned it on, guess what happened...

The arc are very different, instead of a sting of purple light, the arc flaps furiously and it makes very interesting light display. But this is not suitable for a plasma speaker, because the arcs flaps so much it just simply drowned out the music...

Here is a movie of the arcs.

Well, I hoped you enjoyed this instructable!
If you have any questions, or need help, or found an error, or anything, make a comment! I like comments! :-)
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  1. This was really cool. How loud is it? could the open field be enclosed in a glass case and still produce enough audio to be heard?

  2. The simpliest audio plasma circuit, congrats!

    Do you plan a new version? It seems the FET works in linear mode that causes the high temperature.

  3. Are you sure TL494 is properly connected? I see LOTS of errors :)