Instructables
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.





 
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Step 1: 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.

Stripboard

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.


Disclaimer
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.
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NullByte45325 months ago

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?

ljeckel1 year ago
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?
ljeckel1 year ago
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)  ljeckel1 year ago
Hi,

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,
sleepyjz2 years ago
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.

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

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.

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 man1 year ago
u spell favorite with out u
Alex1M6 (author)  radio man1 year ago
Not in the UK we don't.
PCBgroove1 year ago
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.
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 ;-)
Could I ever wire this circuit to audio modulate a tesla coil? I need help somebody please guide me. Haha
Alex1M6 (author)  WeaponsofmyMind001 year ago
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.
mmcnater1 year ago
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)  mmcnater1 year ago
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.
dude can i use 1n80 mosfet(800v N channel) instead of IRF's and is there any other diode instead of UF4007
Alex1M6 (author)  MadGuitarist1 year ago
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.
what about using a 12v adapter
grobgrobin1 year ago
thanks i thought it was me being thick
Alex1M6 (author)  grobgrobin1 year ago
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.
grobgrobin1 year ago
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)  grobgrobin1 year ago
Your right! Looks like I made a mistake there, I will correct it.
phevtron1 year ago
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 http://www.vishay.com/docs/91036/91036.pdf

thank you very much :)
james346021 year ago
Can I use a 24v input at Primary Coil and MOSFET section
Alex1M6 (author)  james346021 year ago
Yes, but you will need to use more primary coil turns.
budhaztm1 year ago
What about this mosfet :
http://www.alliedelec.com/search/productdetail.aspx?SKU=70212479

love the instructable. great job
Alex1M6 (author)  budhaztm1 year ago
That looks fine ( : Make sure you try an RCD snubber too to protect the transistor.
sternmin8or2 years ago
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?
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)  sternmin8or2 years ago
Glad you got it sorted ( : I did mention battery's on step 4 briefly http://www.instructables.com/id/Audio-modulated-flyback-transformer-driver/step4/Powering-the-circuit/

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.

Alex.
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)  sternmin8or2 years ago
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- Alex1M62 years ago
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-1 year ago
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.
RCD snubber2.jpg
jukees1 year ago
Hi, is Irfp250 suitable for this project, (200v 30A Rds(on) = 0.085).
used it in the plasmana's ZVS flyback...
Alex1M6 (author)  jukees1 year ago
Yes that MOSFET will be fine. Its almost identical to the IRFP260 but costs less ( :
Airazz1 year ago
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)  Airazz1 year ago
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.
555 package.jpg
Airazz Alex1M61 year ago
Oh, good to know. Thanks for the advice.
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