Introduction: 555 Timer Based Plasma Speaker

Picture of 555 Timer Based Plasma Speaker

This instructable will show you how to make an audio modulated plasma speaker using a flyback transformer out of an old CRT display, and the all time hobbyist favourite which is the 555 timer chip.

Not only can this circuit be used to produce audio modulated plasma arcs but it functions as a high voltage power source for other projects.

I will be updating this instructable over time.

Note: Please turn up your sound volume, it sounds much better in real life but my camera does not pick it up too well.

You may not, except with our express written permission, distribute or commercially exploit the content. Nor may you transmit it or store it in any other website or other form of electronic retrieval system.

Step 1: What You Will Need

Picture of What You Will Need

Parts list:

1x Flyback tranformer

A flyback transformer, sometimes called a line output transformer are used in CRT TV's and computer monitors to produce the high voltage needed to power the CRT and electron gun. They also have other auxiliary windings built into them that power other parts of the TV.

You can get flyback transformers out of older CRT monitors and TV's. They are the ones that have a big chunky chassis. There are also other instructables on this website showing how to remove them from the chassis and circuit board.

1x Power MOSFET,
I used an IRF540 as that is all that I had lying around. I strongly recommended using a MOSFET with a higher drain-to-source voltage than the IRF540, which is only 100v.

Just for an example IRFP460 would be well suited for this and IRFP250N and IRFP260N would also work. Any MOSFET that is rated for high voltage, has a low on resistance and can take more than 15 amps would be fine.

1x Heatsink

You will need a large heatsink as it will get very hot (more on why later). The TV board you got the flyback from is a good source for heatsinks.

1x NE555 timer chip

I also recommend using an IC socket (8 pin) for the 555 so you can easily remove the chip without de-soldering it.

2x 47 ohm resistors

1x 22 ohm resistor

1x 470 ohm resistor

2x 50K potentiometers

3x 1nF capacitors

1x 220uF - 1000uF electrolytic capacitor (16v will fine).

1x 10nF capacitor

1x 100nF capacitor

1x fast diode, such as UF4007

1x NPN and PNP complementary bi-polar junction transistor pair (if you are following the first schematic).BD139 and BD140 can be used here.


12V power source

Fuse (recommended to protect the power source/supply).

Audio source (This could be an MP3 player or old phone for example).

Solder and soldering iron + some spare wire.

I am in no way responsible if you mess up with this circuit. If you mess up, receive an electrical shock or burn your house down whilst making this circuit you have no-one to blame but yourself. By following this guide in order to make this circuit you agree to accepting all liability if something were to go wrong.

Step 2: Assembling the Circuit - UPDATED (better) Schematic's!

Picture of Assembling the Circuit - UPDATED (better) Schematic's!

This project requires some knowledge on how to read circuit schematics. It is basically a 555 timer operating in astable mode, pulsing a MOSFET with a frequency and duty cycle set via the potentiometers.

I recommend using the first (BEST) schematic. You can use the second one if you do not have any BJT's (Bi-polar junction transistors) to hand.

I do not recommend the third schematic as it uses the same power supply for both the 555 timer and flyback and this can cause problems.

I also added a real world view graphical diagram showing how the 555 timer is connected.

Step 3: Prepering the Flyback Transformer

Picture of Prepering the Flyback Transformer

Using some magnet wire, 26SWG or thicker, wind about 8-12 turns onto the core.

Do not use thin insulated wire as it will melt (I found out the smoky way!).

Step 4: Powering the Circuit

Picture of Powering the Circuit

This circuit requires a 12v supply that can deliver at-least a few amps, which means that most types of battery's are useless for this except for larger lead acid battery's or a power supply that can deliver the current required.

AA cells are pretty much useless for this, they will run down quite quickly. They can how-ever be used for powering the 555 chip if you are using separate power supply's. If you really have no other choice then use them, but the arc will not be very big.

9V /PP3 Battery are a definite no-no. Even for the 555 timer section.

Lantern battery's Should last a good while, providing you limit the current draw by upping the primary coil turns.

12V Lead acid battery's are perfect for this type of thing.

A Power supply is good.

Step 5: Testing It Out

Picture of Testing It Out
Once you have the circuit made you can now test it and see if you get any arc from the flyback. Tweak with the potentiometers until you get the best output (You might also have to switch the polarity of the primary coil).

The MOSFET can get VERY hot even with a good heatsink!

Below is the best output I could achieve from mine using a 12V lead acid battery.

Step 6: Applying Audio

Picture of Applying Audio

Simply connect up your audio source (such as a phone) as shown in the schematics and play an audio track of your liking, you will have to tweak the potentiometers to get the best sounding output.

You will have to find a way of connecting your audio source to the circuit, I used an old headphone cable. I cut it in half and soldered some conductive contacts onto the ends so I can quickly clip my alligator leads onto it and be sure a good connection is made.

See the third picture on this page to see my cable.

In headphone cables gold is usually ground and red and blue are separate audio channels. Just use one of the channels and leave the other unconnected.

An easy way to remove the enamel insulation from the audio cable is to burn it off with a flame.

Note: the audio level from the arc will not be as loud as a regular speaker, that is just the nature of plasma tweeters.

Disclaimer: Whilst I have not personally had any problems using this circuit with my phone, I take NO responsibility if you somehow manage to brake your phone using this circuit. So it might be a good idea to use an older device to provide the audio signal so in the event of something going wrong only it would not be such a loss.

Also do NOT use your laptop or computer for the audio source!

Step 7: How Does It Work?

Picture of How Does It Work?

The 555 timer generates a square wave of a frequency and duty cycle determined by the potentiometers and capacitor across pins 8-7 and 7-6,2. This square wave is applied to the gate of the MOSFET turning it off and on many times a second (tens of thousands) thus allowing pulsing current through the primary coil of the flyback at a frequency generally in the 30-50khz range.

When an audio source is fed into pin 5 of the 555 chip it will actively change the duty cycle and frequency of the square wave to the sound waves of the audio source. This is audible in the arc via the changes in air pressure surrounding the arc, and as it is an audio signal altering this pressure we can hear it as sound.

If you have an oscilloscope then you can view this square-wave by connecting your scope probe to pin 3 of the 555 timer. Connect the scope probes ground clip to circuit ground.

Step 8: Troubleshooting

Picture of Troubleshooting

Q: It does not work
A: Check to make sure that all connections are secure (soldered) and there are no shorts anywhere.

Q: The arc is small.
A: Ajust the potentiometers trying all combinations, there should be a "sweet spot" at some point. If not then reverse the wires going to the flyback transformer primary coil. Most Flyback transformers are polarised and will only work best one way (becuase of the built in diode).

Q: There is no audio.
A: Check for continuity of your audio cable, most likely that there is no continuity there as these wires are very fiddly to get right thanks to the very small conductive strand and thick enamel coating.

Q: It worked but now it does not work.
A: Check the MOSFET has not blown. If you have used a lower voltage MOSFET (below VDS400v ) then chances are that a high voltage spike on the primary has caused it to break down. I originally used an IRF540 that only has VDS100V and it did not last too long before a spike on the primary killed it.

Q: The MOSFET gets hot or shorts.
A: This is one of the major shortfalls of this design, the leakage inductance of the primary coil causes the voltage on the primary coil to rise to a level much higher than the input voltage every-time the MOSFET switches. Avalanche rated MOSFET's can survive for a while, dissipating this energy as heat but after a while it can cause the MOSFET to short.

One way of fixing this is by the use of an "RCD snubber". This is a resistor, capacitor and diode in parallel with the primary coil and it keeps the peak voltage seen on the drain of the MOSFET to a level lower than the breakdown voltage of the device.

Choosing the correct values is not easy and putting anything across the primary coil is going to reduce the final output voltage, since it is this "flyback kick" on the primary coil that is creating such a high output voltage on the secondary coil (in this topology anyway).

As a starting point use a 150 ohm 2w resistor, UF4007 diode and 220nF capacitor.

Also make sure that the duty cycle is not too high, a tell-tale sign of this is a high current draw. This may give the impression of the circuit being tuned in resonance with the flyback but what is actually happening is that the flybacks core never fully resets due to a too high duty cycle, and in worst case scenario the core saturates and the MOSFET goes pop. This is where an oscilloscope comes in useful.

Q: The transformer arcs over like in the video below:

A: Hot glue is your friend here ( :

Step 9: Increasing Loudness

Picture of Increasing Loudness

Want some more volume? Try this little pre-amplifier modification.

Special thanks to Atomicrox.


Mrinal 1 (author)2016-07-10

is there some high voltage present at pin 5 of 555 timer which can kill the audio source

HaroldV10 (author)2016-04-25

I have red wire and white and two magnet wire, how to make

zork the destroyer (author)2016-01-09

the insulation on the wire going to the MOSFET source melts immediately when i power it up. What's wrong?

SmartGuyGoesCrazy (author)2015-02-21


i was using 5v to power the 555 and worked perfectly, when i tryed 12v the capacitor blew up, i was using 1000uf 25v

make sure the capacitor is installed in the right polarity

DiegoR6 (author)2015-01-27

What do "102" and "104" mean in the first schematic?

htownclyde (author)DiegoR62015-09-29

certain capactiors use that as an identification number. Just look it up on google and it will tell you the values

bui anht (author)2015-08-12

i have made best schematic but i got some problem

I use d882 and b772 transistor for the amplifier but when i connect c pin(middle pin) of b772 to mass(atx psu power is on) it cause electric arc and psu auto off,so is it wrong on schematic or i wire wrong?(i think d882 and b772 have base pin is on the right,collector is middle pin,emitter is on the left)?can i use irf840,irf730,irf3205 instead of irf540?i cant find it at my place.the +12v at primary coil,can i wire it to psu or i have to use one more power supply for it?.sorry for my bad english.

AlexC41 (author)2015-06-23

Hey, I've made the best version of this plasma speaker and it works fine. Only problem is it isn't loud enough. I'm using the pre-amp circuit but it is yet to make much of a difference. When prim has13 windings @ 30v it chews 5 amps and has a 35mm spark. At this point it is reasonably audible but not loud enough. How could I make it louder? I am using a old iPod as the audio source but that shouldn't matter? Could it be that C3 is 220uF and not 1000uF? I am using the exact transistor and BJT's for the totem pole buffer stage. I've kept the duty cycle close to 50% and I'm not really using a core spacer.

NullByte4532 (author)2014-03-17

I've tried to make this thing, but I failed. Firstly, it did not work at all, but after a few seconds my flyback exploded. What am I doing wrong? Should I wind primary of flyback myself, I mean before I used unmodified flyback from an old tv. Everything looks pretty well assembled (not as I always do:)), powered by an old ATX power supply. I've also tried with ignition coil, but that did not work. Ignition coil heated up just a bit, but transistor was cold. And what specific type of capacitors should I use?

ljeckel (author)2013-07-01

I tried to adjust potentiometers (100k not 50k) still not bigger. I tried 8 turns too, no improvements.

I don't understand what you mean by "are the cores spacers still inserted between the core halves?"

So the diode I'm using is not what's causing the problem?

ljeckel (author)2013-06-30

Hi! I built this project but my arc is pretty small (1,5 cm max) i'm using a 12v 20 amps atx psu but i measured only 2-3 amps on the primary. The primary coil doesn't even heat up! i use small wire i did 10 turns for the primary. I tried to reverse the polarity, it was smaller. I'm using a 6 amps mosfet for now. Could it be the diode ? i'm using a By329 which isn't as fast as the uf4007 (135ns). Using the best schematic. Sound is very weak too (due to the small arc I guess). Can you help me here please ?

Alex1M6 (author)ljeckel2013-06-30


Have you tried adjusting both of the potentiometers? as there will be a "sweet spot" where the flyback will produce the best arc. If you have already done that then I would also try removing some primary turns, perhaps try 8 turns.

Also are the cores spacers still inserted between the core halves? If not then they need to be.

The audio volume can be greatly improved by using the pre-amplifier on step 9,

sleepyjz (author)2012-08-16

I built this, the circuit seems to be running fine (the heatsink + fet also make a great fast acting personal heater!). I tried a cassete player for and a CD walkman, both dated technology but it was just to test the stuff. The problem is, the audio is VERY quiet and I'm not sure why. It's nothing compared to the volume you got going with your arc in the video. It's almost concealed by the noise of my power supply fan. I'm using the BEST schematic with two supplies.

Any Idea what's going wrong with the audio? I'm using right channel and ground, headphone wire continuity with the circuit is solid. Tried a couple of different flybacks too.

You have got to see the results of using this driver with a "sampo" brand computer monitor flyback.....Internal capacitors are scary as hell. Youtube channel coming soon :p

sleepyjz (author)sleepyjz2012-08-16

Scratch that. A boombox plugged in to a wall delivers good volume.

circuitmage (author)sleepyjz2013-06-20

I noticed that too.

It looks like the pre-amp is important. I tried a late 80's Sony Walkman...nice blaring audio compared to modern (lower power) audio output. A more robust audio source the better. Have not tried added pre amp circuit, but that looks like a good idea.

circuitmage (author)2013-06-14

As a check, before you hook up the Xfrmr, you can hook up an 8ohm speaker on 9V in place of the Xfrmr. You can hear the oscillation from the 555 and even tune it abit using the 2 pots. This will verify your 555 wiring and verify the xstrs and FET are working.

radio man (author)2013-05-24

u spell favorite with out u

Alex1M6 (author)radio man2013-05-24

Not in the UK we don't.

PCBgroove (author)2013-02-28

From all the comments I see here, its lack of electrical engineering going on. My experience with mosfets is the RDS lends to dampening or raising ringing in the feedback loops. That will kill you every time and lead to hot Mosfets. You have to know what your doing with these and sizing cooling based on a non ringing circuit. Additionally, I would use an led and a receiver to decouple the 555 from the output circuit too and remove the danger of electrical shock hitting your telephone with 2000 volts. Another thing too are the back emf's these are transient based and can lead to slowly destroying your output mosfets. If the frequency can be adjusted to limit say at 8 khz, IGBT's are your best bet. Then the problem is the 8khz can be heard. If still using mosfets, you better spend a few hours looking over all the data sheets information, have a engineering background to deal with this and better buy perfectly matched transistors in your paralleled output circuit. Your output is only as good as the weakest link as all the power will be sucked there and then the projects really sucks. I think its neat what your doing but its a science fair project. Otherwise Sony would already be building this.

Why not work on the real issues the sub-woofers that are very expensive, and amps to drive them. The mid-range and tweeters have already been figured out.

TECHMASTERJOE (author)2013-02-21

S3 will work better if you add a 1200~2200uf Cap rated at main voltage x2 to the main line.
as close to the fly-back transformer as you can so Base of Q1 and 12V main at the transformer. ..

and adding some type of clamping on the transformer feedback might help make the sound a lot better but will make the arc smaller.
high speed diode like UF4007 and a 2ohm 1 watt resistor in series across the transformer P-coil might make for quick and easy testing good testing.

let me know how it go's if you test the ideas ;-)

WeaponsofmyMind00 (author)2013-02-05

Could I ever wire this circuit to audio modulate a tesla coil? I need help somebody please guide me. Haha

It wouldn't be very efficient using this design. Head on over to the 4hv forums for questions and I am sure the community will able to help.

mmcnater (author)2013-02-15

I have a 30V, 5A DC power supply. Do you think I could just connect two jumpers at the inputs to the circuit to the single output of the supply so the voltage divides, or would that cause a problem?

Alex1M6 (author)mmcnater2013-02-16

Hi I am not quite sure what you mean here, could you describe what you are trying to do in more detail.

Do you mean just using the 30v supply for both the 555 timer directly and flyback? if so then that will not work since the max voltage the 555 timer can run off is 16v for most versions of the chip.

If you put a voltage regulator such as the LM7815 between the 30v supply and 555 timer then that would work, just be sure to use lots of decoupling capacitors and a fuse between your power supply and circuit.

MadGuitarist (author)2013-02-01

dude can i use 1n80 mosfet(800v N channel) instead of IRF's and is there any other diode instead of UF4007

Alex1M6 (author)MadGuitarist2013-02-16

The on state resistance of that MOSFET is too high for the voltages being used in this circuit. Any fast recovery rated diode can be used in place of the UF4007, just make sure it has similar ratings.

MadGuitarist (author)2013-02-01

what about using a 12v adapter

grobgrobin (author)2013-01-31

thanks i thought it was me being thick

Alex1M6 (author)grobgrobin2013-01-31

I think I might have had a bit to drink when I uploaded it ( : Now I wonder how many peoples circuits haven't worked becuase of this mistake.

grobgrobin (author)2013-01-31

hi there in the best set up u got Q3 pnp with arrow come out at the bottom and when i look on ebay to buy one it shows a npn with arrow coming out tho bottom is Q2 and Q3 number mixed up

Alex1M6 (author)grobgrobin2013-01-31

Your right! Looks like I made a mistake there, I will correct it.

phevtron (author)2013-01-16

greetings and congrats for your excellent and clear guide.
i really wanna know if the irf640 with vdds=200v and ID=18 amps at 25celsius
is suitable for this project , here is the schematic so you can take a look

thank you very much :)

james34602 (author)2013-01-08

Can I use a 24v input at Primary Coil and MOSFET section

Alex1M6 (author)james346022013-01-11

Yes, but you will need to use more primary coil turns.

budhaztm (author)2012-11-18

What about this mosfet :

love the instructable. great job

Alex1M6 (author)budhaztm2012-11-19

That looks fine ( : Make sure you try an RCD snubber too to protect the transistor.

sternmin8or (author)2012-02-13

So I just built essentially this circuit except the transformer is on a seperate power supply. When I hook it up to the transformer i can hear a faint humming sound that goes away rapidly. When i hook it up to a 8 ohm speaker the sound seems to dampen. If I touch the mosfet heatsink while the speaker is dampening it seems to become louder again.

I am using a 12v cpu power supply capable of several (around 12) amps. Is the capacitor across the mosfet important because I do not have it in my circuit. What does it do?

sternmin8or (author)sternmin8or2012-02-22

I have discovered the problem. I was using a 9v battery to power the seperated 555 timer circuit, however I had a buffer stage in it and for whatever reason the buffer stage and the 9v do not like eachother (at all). Which is why it dampened. When I touched the mosfet I gave it some form of extra grounding (maybe?).

Long story short: 9v batteries were the invention of satan and should all be destroyed

Alex1M6 (author)sternmin8or2012-02-22

Glad you got it sorted ( : I did mention battery's on step 4 briefly

An NPN and PNP totem pole BJT buffer stage? If so I think possibly the high peak current draw of the gate charging might have drawn down the 9v's so much that the voltage sagged. Also you might have shoot-through happening and both BJT's turning on at the same time causing the 9v's to short.

Also if you are using separate supply for the 555 and flyback (which I recommend) then remove R4 and make R3 22 ohms. This will help switch the MOSFET faster.


sternmin8or (author)Alex1M62012-02-23

Never mind, I was completely wrong. A battery would have worked just fine If i had attatched the two power supply grounds together. I had forgotten that the current to the mosfet gate had to get back to the negative terminal of the battery D:

The diode and the capacitor across the mosfet are to prevent surges? Or do they help keep the mosfet cool/increase arc length? I have a 500v mosfet so i dont think I need to worry about surges, but if adding those components will make the arc better then I am all for it,

Alex1M6 (author)sternmin8or2012-02-25

lol, I guess you can say you learned something about how MOSFET's work whilst making this ( :

The diode and capacitor is there to help reduce the back-emf voltage spikes that will be produced on the primary side when the MOSFET turns off (its also one of the reasons the MOSFET gets so hot because it is avalanching every cycle).

You *might* be ok with that 500v MOSFET but its always good not to let the MOSFET's breakdown voltage be the only thing protecting it. If your MOSFET does blow then you need a larger capacitor here.

I have also found putting a small MKP capacitor in parallel with the primary coil helps reduce the voltage spikes and MOSFET heating a little. It makes the arcs smaller but thicker though.

As for making the arcs smaller, putting anything there that reduces back emf spikes will make the arc slightly smaller but its a compromise between arc length and durability. The only reason you get such a high voltage on the secondary coil is becuase of this back emf spike, if you were to put a diode in reverse with the primary coil like you would with a motor or relay then you would remove all back emf spikes but arc length will be much smaller becuase there will be no "flyback kick" to further boost the output voltage.

I also recommend having a permanent arc gap set up for the arc to take place, rather than always drawing arcs and moving the arc around. I say this becuase the back emf spikes are different depending on how much you are loading the secondary coil of the flyback, and with no arc at all or if the arc is unstable the back emf will much higher than if you had a steady arc going.

Hope this helps.

-max- (author)Alex1M62012-05-23

so would a capacitor / diode in series be the best to put across the primary to keep the back-EMF at bay?

i was thinking, what if you put the diode in between the primary and the transistor? like

+12V -> one side of primary -> other side of primary w/ small capacitor across it -> DIODE -> mosfet with backwards diode-> ground.

and also have zener diodes put together across the gate, so any overvoltage (<24) to further protecy the mosfet?

and havee you tried IGBT's? do they work any better?

Alex1M6 (author)-max-2012-11-18

Sorry I have missed your comment up until now. The way they commonly do it in commercial power supply's that use the flyback topology is to put an "RCD snubber" in parallel with the primary coil. This dissipates the energy stored in the leakage inductance of the primary coil and thus prevents the back emf voltage from raising above the MOSFET's max breakdown voltage. The MOSFET getting hot in this design is mostly caused from avalanching.

Yes you can use a zener diode to protect the gate, use a 12-18v one with cathode to the gate and anode to ground.

See the image I have attached.

jukees (author)2012-11-18

Hi, is Irfp250 suitable for this project, (200v 30A Rds(on) = 0.085).
used it in the plasmana's ZVS flyback...

Alex1M6 (author)jukees2012-11-18

Yes that MOSFET will be fine. Its almost identical to the IRFP260 but costs less ( :

Airazz (author)2012-11-12

My local electronics store has both NE555D and NE555N timers. Is there any difference which one I use? The price is the same.

Alex1M6 (author)Airazz2012-11-12

Hi, yes there is a difference. They are both the same chip but the NE555D is a much smaller version and are a complete pain in the ass to solder by hand.

See the image I have have attached to this reply for comparison.

Short answer: Get the NE555N.

Airazz (author)Alex1M62012-11-15

Oh, good to know. Thanks for the advice.

baven (author)2012-09-17

Hi there i got a problem with this circuit. I adjusted the frequency and Im using
the BEST schematic but when I turn on the 555 oscillator and connect the primary
coil to power it gets very hot and no arcs on secondary. Any idea where the
problem could be?

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