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Plasma speaker: now with Nice Box!

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Shaun

Tue Jan 06 2009, 06:53AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

This was a small project I decided to undertake while home from college during winter break. Now its done, and there's still another week and a half of break left...maybe I work too fast/much.

Anyway, I wanted it to be something small I could build over break, and still be able to take back to the dorm without freaking anyone out. That meant:
-not lound
-not [very] dangerous
-low power consumption
-low interference
-must be neat

After all that I decided to build Jan Martis's audiomod flyback driver. It seemed to fit all the criteria, and I also had all the parts to build it on hand, so no online orders needed.

The circuit is what I believe to be the most recent one, and as an output stage I chose a mains-fed (120VAC) half bridge of IRFP250s running at 100kHz. I thought that might be cutting it close to their max voltage, and I have TVSs in there but it seemed to work fine without.

The flyback is my biggest and most reliable one, which survived much abuse in my ZVS driver without a scratch on it. With a 20 turn primary I am running it at slightly over 4V/turn, which should be fine at such a high drive frequency. The core gets slightly warm after 15 minutes of continuous runtime.

The sound quality is amazing; much better than my laptop speakers (HP Pavilion), and can get pretty darn loud before I start hearing distortion.

This first pic is the finished product sustaining an arc. I'm very proud of how it turned out, and I think it'll look great on my desk in the dorm. On the front is the only control, the On/Off switch. Volume is controlled by the source device. On the left face is a 3.5mm jack for audio in, and on the top two short bolts serve as HV output. Right now two copper wires form the electrodes, but soon I'll replace them with something more adjustable. And that doesn't melt...

This is by far my nicest looking project, but what really gets me is the fact that NOTHING WENT WRONG. I'm almost scared at this point. I have blown no components, fuses, or anything else throughout the entire process of building and testing this. That's a big first for me. Of course now I'll turn it on tomorrow and it'll explode in my face and catch fire.

I have a pic under the hood, but I can't seem to attach it. Maybe later.

uzzors2k

Tue Jan 06 2009, 10:01AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Nice. I bet it will get a lot of attention at the dorm.

Zorink

Thu Jan 08 2009, 08:00PM

Registered Member #1292 Joined: Wed Feb 06 2008, 04:09AM
Location: Mesa, AZ
Posts: 25

I googled around for
Jan Martis's audiomod flyback driver
but couln't find any schematics. Can you post them?

Dr. Dark Current

Thu Jan 08 2009, 09:01PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Shaun, congrats, I like to see people building my circuit without exploding anything

And I'm glad you like the sound quality.
Just be sure not to overload the input as there is no protection of the frequency getting too low -> exploding the bridge.

For anyone interested the schematic link is here:

(there's a lot of comments on the drivers etc., the "better output stage" is just a simple half-bridge and the description is there so that even people less keen on switching inverters can build it... Also Vs should be Vd as it's "drain supply", but you could also say that Vs is "supply voltage"

)
Btw. Adding zeners to the gates might be a good idea.

Edit: My FTP server is down right now, I wanted to update the schematic with just 15V supply for the SG3525 because with 12V the FETs might get quite bit warmer...

I don't have any website and probably never will have one, as I never finish it (and I've started lots of times!

) Guess I'm just lazy or have other things to do... (and not much pictures of old projects to add)

Edit2: Schematic updated.

Littlew

Sat Jan 10 2009, 04:58PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

too thin wire, it will start melting after 1 minute of arcing

teslacoolguy

Mon Jan 12 2009, 03:21PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

I know it's totally overkill but you think the circuit would work with 30n60 igbt's? Also, why not keep the power supply at 12v and just make a 1:2:2 gdt?

Dr. Dark Current

Mon Jan 12 2009, 03:47PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

teslacoolguy wrote ...

I know it's totally overkill but you think the circuit would work with 30n60 igbt's?

Probably but you might need to boost the controller output with gate drivers.

teslacoolguy wrote ...

Also, why not keep the power supply at 12v and just make a 1:2:2 gdt?

Because you would have too much voltage on the gates. Also, the higher voltage for a gate driver, the cleaner the signal. 1:2 GDTs theoretically have 4x higher leakage than 1:1 ones.

rp181

Mon Jan 12 2009, 11:34PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Nice.
You should replace the wire electrodes with something thicker and solid (like 2 bolts), it will look better.
Any comparison for how loud it is?

teslacoolguy

Tue Jan 13 2009, 01:27AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

possibly a video on youtube?

Shaun

Tue Jan 13 2009, 03:54AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Littlew wrote ...

too thin wire, it will start melting after 1 minute of arcing

rp181 wrote ...

You should replace the wire electrodes with something thicker and solid (like 2 bolts), it will look better.

You can see I've wrapped the copper wire around two large bolts in the case, which will be attached to an adjustable spark gap of some sort once I get around to going to the hardware store. And no the wire don't melt, even after 20+ minutes of continuous operation. They did melt a little bit when I first fired it up, then formed a bead which stays solid.

teslacoolguy wrote ...

possibly a video on youtube?

As much as I'd like to I don't have a working camera right now, sorry. However, I do have a pic "under the hood":

Looking at that pic again I'm kinda surprised I don't have any internal arcing problems.

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