A reliable plasma speaker

I've seen multiple designs for a plasma speaker online, and quite frankly most of them suck. Some problems I noticed were constantly blowing up MOSFETs, distorted audio, excessive heating of the MOSFET(s) etc.

I was alerted to a nice circuit on 4HV that uses a half bride and pulse width modulation. I modified the circuit to my liking and it worked very well.  Extremely well.

So in this instructable I'll show you how to make the speaker that's on my website. Properly heatsinked it can run continuously, I have run mine for a length of about 6 hours with no problems.

Below is a video of this speaker in action. It sounds better in real life; my camera just doesn't have too good of a mic.

Step 1 Gather the parts

You'll need some parts for this speaker, not too many but some.
You'll need:

Components:
4x  UF4007 diodes
4x 12 volt zener diodes
2x  IRFP250 mosfets. You can also use some better fets, the lower the Rds On the better. Just make sure they can handle at least 200V, flybacks make some nasty back EMF.
1x  SG3525 IC
1x LM7812
2x  22 ohm resistors
1x 2.2k resistor
1x 10k pot
2x 0.1uF (104) capacitors
1x 3.3nF (332) capacitor
1x 1uF (105) MKP capacitor
1x 2.2uF electrolytic capacitor
2x 10,000uF electrolytic capacitors If you use 40v 8000uF caps instead you can apply 36V and make the arc even bigger and louder. Just make sure to replace the 7812 with a 7815 or a 7818.

Other components:
A flyback transformer. You can get these out of old computer monitors, TVs etc.

A ferrite toroid. These may be inside computer monitors, but if you can't find one get it here.

Some 18ga wire.
Some 24 ga wire, the wire from inside of a telephone cable works great.

2 heat sinks, you can get them from a computer monitor. You'll need to use your scavenging abilities here.  If you use 1 heat sink make sure you use some insulating pads.

Thermal goop.

Comments

[rtty21]

What does this piece do for the circuit? what is it usually used for?

[-max-]

to get the mosfets out of phase (so one gets an inveted signal, and what will happen is when one mosfet is on, the other of off, vise versa,) that needs to be done so the two fets drive the primary and not short themselves out when the signal is high.

[grenadier]

What piece do you speak of?

[Whatnot]

If you go to step 2 'making the GDT' you'll see that tyyu21's comment is the only one there, so I guess he means that.
Instructables just bunches all comments together on page one too causing the confusion.

[grenadier]

Ahh, OK.

Its purpose is to isolate the mosfets from the IC.

[tank1357]

How did you arrive on 14+ turns?

[rtty21]

How does the GDT isolate the mosfets from the IC?

[grenadier]

I just did what worked best.

[Minifig666]

It's a transformer. The IC gives out high(ish) frequency square waves and they are induced from the coil on the IC to the coils going to the MOSFETs. Because there is no physical connection they are said to be isolated.

[rtty21]

thankyou!
XD

[carldong]

Hi, I made this circuit as two parts: one with SG3525 and two totem poles for generating square waves, and another for half bridge. However, the half bridge dowsn't work, and I am wondering will a low quality winding on GDT will stop it from working? I've checked the waveforms on both MOSfets, they are right and reversed. But I cannot get any output from the board if I increase the frequency to about 4kHz. Anyone with any ideas?

[playpep]

I would love to build a set of these for use these at the golf course.{lots of rich kids who have some pricy toys, and i need some leverage} i am doing some research and want to know how loud you can make these. Great illustration of the circuit and please let me know. I want to get my information from someone who has experience in their production.

[Top-Dog]

Does anyone know how to make the arc sound/look bigger? Could you just power the circuit with a higher voltage (and power the ic seperatly off a lower voltage)? Also, if only 2 large caps are needed why does the picture show what looks like 10 large electrolytic capacitors?

Thanks

[Blaneparker]

Put you cursor over the compactors and it will tell you why.

[Blaneparker]

What would happen if you touched only one of the leads? Or if you put a finger between the two leads?

[spyrusthevirus]

how loud is this thing?
how can it get louder? From what I understand, a biger arc will be needed for more sound, and higher voltages will be needed for a bigger arc. How big is this "bigger"? Is pluging the whole thing on the wall safe enough or are we risking frying something? :P
The batteries you are suggesting, for how much time can they power the speaker before they empty? Is there any solution that is renewable in the sense that it can be used over and over again without buying new ones-even with some recharging (if using the houses power supply is out of the question).
For the flyback, I don't have anything old available in order to scavenge. For what features should I look to get good performance?
In the videos I notice there is some noise from the arc jumping around. Would a fatter cable or a "big" (say, .5cm diameter) electrode help reduce that?
And to end the torrent of questions, about how much power does the whole thing draw? I'm guessing it's quite energy hungry.

Neat idea.

[Blacklight [HUN]]

I need a little bit of help :S
I built the circuit and ran it from a laptop charger at 12 V. It worked fine, until I increased the voltage to 24 V. The circuit simply stopped working. I checked every soldering and wire on the board, and all of them are fine. What could be wrong?
There is no voltage between the wires which go from the board to the flyback.
PS: I used exactly the same parts listed in step 1.

[Alex1M6]

Hi, I just made this but the chip gets very hot but I connected everything up correctly.

any ideas?

[kovama1]

Hi I solved this problem with changing toroid. Before change i used yelow from PC power supply, but chip got realy hot. Then I found one black and chip is cold :-) This is my speaker but stability of arc is horrible I thing that could be in 10k pot I'm going to buy better one. http://www.youtube.com/watch?v=Us7lu6PorJk 
(P.S. sorry my english :-))

[Alex1M6]

Hi, I managed to solve it too by also swapping out the ferrite core I was using but I also went one step further and used a totem pole stage between the chip and GDT. The chip stays cool now and the MOSFET's also stay cooler. I have found using a 50k in series with a 10k pot works much better as it allows for a much wider range of frequency's to be selected because of the 50k but the 10k still allows you to make small adjustments as the 50k on its own can be quite sensitive.

Here is mine

Alex.

[kovama1]

Could you please draw it in this schem? http://teravolt.org/Plasma_Speaker_2_files/schem.png ? :-)

Thanks

[Alex1M6]

Its not my website so I can't.

[kovama1]

Why not use operational amplifier instead of the toroid? It could work? :-)

[Alex1M6]

No idea, never used one before.

[Blacklight [HUN]]

Are any MOSFETs good if they can handle 200V and at least 20A?

[adeebm]

I just built the circuit on my breadboard for the 4th time, and the strangest thing is happening. One or more of the components seems to be resonating and playing the song. To clarify, I have the full circuit build on the breadboard, hooked up to audio. When I connect the flyback, I get almost nonexistant sparks. With OR without the flyback, one or more components on the breadboard is resonating and can literally hear the song being played with no spark. The sound seems to be coming from the MOSFET side, but I can't be sure. What's going on here? Since the flyback isn't hooked up, there can only be 12v running through the board, not enough to arc, so how can there be sound?

[grenadier]

I'm just as stumped as you are.

[adeebm]

If I remove the mosfets from the circuit and keep everything else in place, the audio starts to come from the ferrite toroid. When I place the mosfets back in, I'm not sure where the sound comes from, but it gets louder. Also, when I pull one of the cap leads out and place it back, it sparks makes sound. I wonder if the breadboard or something internal is sparking. Maybe I'll have better luck on perfboard.
Here's a video of the circuit:
http://s463.photobucket.com/albums/qq358/adeebm_photos/Random/?action=view&current=ac26b66a.mp4

[dragonriot]

Do these things provide any bass, or is it all treble? It seems in all the videos I've ever seen of a plasma speaker, it's very high pitched, even when the song should be pretty low.

[Alex1M6]

I would say they are more suited for being a tweeter.

[Feca]

Ok, i've finally decided to make this. The only problem is that i cant find any IRFP250 mosfets, however i have a bunch of IRFP254 mosfets. My question is will they work as a substitute to IRFP250 and will I need to make any modifications to the circuit itself later?

[Alex1M6]

IRFP254's will work fine without any need for modifications.

[Alex1M6]

Here is mine up and running on 36v input

I have also now added a totem pole transistor buffer stage between the chip outputs and GDT to help reduce MOSFET heating, which it seems to working somewhat.

[Alex1M6]

Wouldn't more secondary turns on the GDT help make sure the MOSFET is always saturated?

[grenadier]

I'd give it more inductance yes, but you'd need more driving power as well...

[Alex1M6]

Is the SG3525 chip meant to get hot? My chip is getting very hot within about 10 seconds.

[Brubouy]

Yeah !! It works, I made my own PCB for the project using FreePCB, that was a project in its self. I bought the copper coated blank and acid from Radio Shack and used the lazer jet transfer method to mask the board. I used a 24v 5 amp power supply from bestdigitalusa (EBAY) $16 +sh and the MKP cap that digikey is out of, I bought from http://www.tubesandmore.com. I made a cool mahogany and polycarbonate to house the whole thing. Thanks to the author!!!

[Alex1M6]

Does your chip get hot?

[Alex1M6]

To anyone ordering from farnell in the UK get these capacitors http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1198552 , for 50v @ 10,000uF there are pretty compact!

[altaholic]

The 1uF capacitor isn't available from digikey or mouser. What is a good substitute I could use?