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Some thoughts about Plasma Speaker designs

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Steve Conner

Tue Mar 29 2011, 09:19PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Do the flyback transformer kind even qualify as high-fidelity? I heard that you have to run at 3MHz or higher to make the hissing sound of the arc go away. The Ionovac used 27MHz. A flyback can't handle more than a few hundred kHz.

Of course IMO none of them count as high fidelity compared to a humble dome tweeter.

Dr. Dark Current

Tue Mar 29 2011, 09:23PM

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

Steve: I think the hissing problem is worse with "single ended" discharges such as a SSTC. If the electrode-to-electrode discharge from a transformer is kept stable and suitable electrodes are used, the hiss can be pretty low at tens of kHz but of course it doesn't disappear completely.

Xray: I have a schematic but it is in Czech only, sorry.
Pulse width modulator:

Power inverter:

Steve Conner

Tue Mar 29 2011, 09:36PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Dr kV, I like the gate driver made with one UCC and one IRF540. Took me a while to figure that one out

Xray

Wed Mar 30 2011, 12:00AM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Dr. Kilovolt wrote ...

Xray: I have a schematic but it is in Czech only, sorry.
Pulse width modulator:

Power inverter:

That demo video of your plasma speaker

sounds pretty decent! Your arc is quite a bit longer and fuller than many of the ones I've seen on YouTube, and that contributes a lot to its good overall frequency reproduction and volume. Nice job!

Tightmopedman9

Wed Mar 30 2011, 07:13AM

Registered Member #3197 Joined: Tue Sept 14 2010, 04:56PM
Location:
Posts: 19

Steve McConner wrote ...

Do the flyback transformer kind even qualify as high-fidelity? I heard that you have to run at 3MHz or higher to make the hissing sound of the arc go away. The Ionovac used 27MHz. A flyback can't handle more than a few hundred kHz.

Of course IMO none of them count as high fidelity compared to a humble dome tweeter.

Once my plasma speaker is complete I'm going to do a THD analysis using some equipment from school. After that I'll hopefully be able to analytically answer the hissing problem.

Shrad

Wed Mar 30 2011, 08:23AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

have someone ever thought of using a class D amplifier chip?

they have everything needed in internal audio circuitry, some have external clocks you could maybe drive with a 4046 PLL, and some have a H bridge driver output...

Steve Conner

Wed Mar 30 2011, 08:53AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The problem with a class D amplifier is that the PWM is wrong, it's unipolar. So it will just saturate a transformer and burn it out.

A Class-D amp would make a good high-level modulator for a Class-E MOSFET RF amp. I seem to remember Richie Burnett made a plasma tweeter this way.

doctor electrons

Wed Mar 30 2011, 10:19PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

The coil in the video from your first post is the one from EVR. That is the class-e that uses the am modulation.
I gotta say, that coil sounds pretty amazing. The arc is about as close to silent as you can get i suspect. You do
hear a faint hiss when the arc changes position if you have the ring electrode set up like in the video. I actually have
3 of that very coil, 2 set up for stereo and one i put together with my nephew. The video does NOT do it justice. The sound
is awesome and even the low end is very audible. I built mine with a special purpose in mind (referring to the actual resonator)
that would reflect most of the sound back out of the coil forms instead of trapping it. I also vented the bottom of the base and
raised it off of the ground to let sound escape from the bottom as well. The ring electrode does help the sound quite a bit to.
The ring creates more surface area for the arc which is what vibrates the air. It is much louder and near cd quality if not cd
quality. Maybe EVR can chime in with some of the nitty gritty details on his kit that would help more. Its a top notch set up
in my opinion, thats why ill probably be getting another one to complete a second stereo pair!

Arcstarter

Thu Mar 31 2011, 03:16AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Just modulate the screen with whatever voltage it requires and you have beautiful audio mod :P

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