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.

So, In this instructable I'll show you how to build the speaker that's on my website. Properly heat-sinked it'll be able to run continuously; I have run mine for a length of about 6 hours with no problems.

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

[SirLordCrazyFish]

Thanks, I just made my first plasma speaker and it worked. I have looked at others, but none have been this easy to build. So once again thanks. Keep doing what your doing.

[Itchago]

Would it be possible to swap out the flyback to a ignition coil?

[grenadier]

Nope; you'd just inductively heat the coil's core at these frequencies.

[seabeepirate]

Alright, I really like this project but it seems more than a little over my head still. My question is, can I use a 555 type PWM and attach the portion of your circuit from the GDT to the Flyback, to the output of the 555 PWM?

[grenadier]

Should be possible, yes. But the 555 timer isn't push-pull, so you might have issues driving the transformer.

[grenadier]

(removed by author or community request)

[seabeepirate]

OK. What voltage and current levels will you see at the input of the GDT?

[seabeepirate]

The reason I ask is because I'm considering attempting an Arduino project and I want to be sure the Arduino can power the GDT, or if necessary I'll build go-between to amp up the Arduino output.

[grenadier]

Yeah you're going to need an amplifier for that one. Keep in mind though, an arduino isn't going to be able to produce a 50kHz frequency modulated signal...

[seabeepirate]

I understand, but I think the signal it can give will be high enough that it won't be horribly annoying. I'm sort of trying to virtualize part of the circuit with the Arduino until I get it working. It's really more of a learning tool for me, if I can figure out how to code it then I should be able to transpose that code into a physical circuit and replace the Arduino.

I think I can build a circuit to invert half the pulse signal of the Arduino or 555. I need to load it into my simulator and try it.

Thanks for all your help, If I get it all worked out I'll try to post a video or maybe an instructable of my own.

[mmcnater]

I have a 30V/5A DC power supply. Will that work, or does it need 10 amps [at least?]

[billgeo]

Hello,

Great design! I'll give it a try!
I realy like the gate driving toroid idea!

About the MOSFETs now, I am trying to find one with low on resistance
but I think the turn-on delay and rise time will be nice to be low as well.

What do you think?

Also in a 36V setup (3 x 12V battaries) would a simple 7815 sufice?
What do you calculate the voltage drop to be there, and the current as well?

Thank you in advance!
Again, nice work!

[billgeo]

I think the rise time of the MOSFET should allow for the PWM frequency.
What frequency did you find works best?

Also what do you suppose is the max current through each MOSFET?
Would 20A continuous be enough?
I am looking at the IRFP360...

[bauerm6]

What do the zeners do? I've got this set up with a 36v power supply and I keep shorting them.

[grenadier]

Protect the gates from too much voltage. In your case they're either; A) in backwards, or B) Getting hot because something else is terribly wrong.

[jmoreira2]

Hey man, I have a question abou the zener, how is it polarized? I cant tell from this diagram and cant access the schematics.

[deaks]

try the diagram on this page: http://forum.allaboutcircuits.com/showthread.php?t=51525

[AznINVazN]

dude, that circuit diagram is so difficult to understand... I'd rather traditional

[grenadier]

Read the text again

[mdbarrett]

I agree with AznINVazN - that diagram won't help anyone. One can read the text 10 times over but it won't change the fact that the link you provided also doesn't work.

[deaks]

you can view a page with his diagram on it at: http://forum.allaboutcircuits.com/showthread.php?t=51525

[deaks]

you can view a page with his diagram on it at: http://forum.allaboutcircuits.com/showthread.php?t=51525

[hginter]

Ty for the quick answer, but I also can't find 8000uF/40V capacitors, will 8200uF/50V work with 36v?
Also, I'm trying to find some higher quality MOSFETS, by "lower the RDS" you mean lower closing resistance?
AND is this ok as the voltage reglurator when using 8200uF caps?
http://ee.farnell.com/fairchild-semiconductor/lm7815ct/ic-v-reg-fixed-15v/dp/1467366

[grenadier]

50V is the maximum voltage the capacitors can withstand; running them at 36V will be fine. The regulator will need a big heatsink though if you choose to run the circuit at 36V

[hginter]

Hey, I can't find a MKP 1uF capacitor with 63 VDC and 25 VAC.
Do the VDC and VAC matter? Does the material matter?

[grenadier]

So long as it's rated at >50WVDC it'll work.

[luig]

if i try to build the 36V version can i use 50v caps instead of 40v caps and do you mean you need a total of 16000uF instead of 20000uf in the 24v version.

[jensenr30]

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?

[jensenr30]

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.

[jensenr30]

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