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Class D Switching Power Amplifiers and Power D/A conversion

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Old 7th May 2009, 01:08 PM   #11
wg_ski is offline wg_ski  United States
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If this isn't just a car SPL competition but some sort of outdoor noise testing a traditional amplifier/loudspeaker may not be the best appraoch. This may not be all that crazy if you think outside the box a bit. If you can live with the noise being a little "whiter" than pink, an amplifier isn't really needed. Ever look at the waveform for the "MLS impulse" used for typical gated loudspeaker response measurements? It's a series of pseudo-random spaced pulses of "unity" amplitude. If you limit the "bandwidth" to a kHz or so, pulse widths can get wider, well within what big-*** IGBTs can do. You end up needing a big +/- power supply (10kVA isolation trafo, rectifiers and caps), and IGBTs to slam it rail to rail driving the loudspeakers directly. If the woofers are horn loaded with a very long (50 foot) path length you could get efficiency down in the teens or lower. The horn wouldn't even need to be permanently assembled - build it so the panels pin together any time you set this rig up. To get to 500 Hz, it may, however, require a 2-way. The upper frequency horn would be easy to build with a high-EBP 10 or 12". The horns themselves would filter harmonics and aliasing frequencies significantly.
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Old 7th May 2009, 01:50 PM   #12
acid_k2 is offline acid_k2  Italy
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wg_ski

I was thinking at it.

big power supply, NE555 for square waveform output, signal trasformers for driving IGBT or high-voltage MosFET (on-off).

The same ancient NE555 may be used to modulate a low-frequency PWM signal, so you could have a very low-fidelity bass amp.

The "core" of that pseudo-amp is simple, but power supply and output filter cold be very difficult to build.
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Old 7th May 2009, 03:03 PM   #13
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Wow! That was a lot of responses since last night! Let me try to answer some questions first, as I realize that this is not your usual living-room hi fi project.

Actually, I'm designing a test chamber that will be used to qualify components for an unnamed space industry contractor. These are components that must be rugged enough to withstand a rocket launch. Literally!

The chamber will have an internal volume of about 60 cubic feet and be made of heavy steel. There will be four Kicker 18" SoloX speakers at one end, plus eight midrange drivers. I need the power amp mostly for the Kickers, and it looks like four of the Labgruppen FP14000 pointed to by peranders will fill the bill nicely! Thanks peranders! I had no idea such big amps were commercially available. I couldn't find them when searching the web for some reason.

I have to use speakers so that I can shape the frequency spectrum in the test chamber, which I will be recording with two microphones, digitizing, and FFT analyzing via computer for subsequent analysis.

SPL drag races, eh? I wish I had some copies of photomicrographs of coclear hair cells after exposure to high noise (those are the sensitive elements in the microphones on each side of your head) to share with you. Normal hair cells are in neat, tidy rows that look something like wwwwwwwwwwwww, and after high noise exposure they look like a forest that has just been through a hurricane. Or maybe a stack of "pick-up" sticks. And they DON'T grow back! Just a thought.

Anyway, if the Labgruppen amps are'nt too pricy I'll be going with them. I've got to admit, though, that after reading quite a bit on this site yesterday I've kinda got the bug to try building one of these babies. I REALLY like the elegance of the class D approach! We'll see!

It's been a pleasure meeting you guys, and thanks for all the responses!

BillyDoc
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Old 7th May 2009, 03:30 PM   #14
Electrons are yellow and more is better!
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Please note that 14 kW is under certain circumstances. If you want continuous power you must seek some industrial amp running on three phase power. I ran into such amp at SAAB Aero Space which drove a shake table with it.
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Old 7th May 2009, 03:34 PM   #15
Electrons are yellow and more is better!
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Inspiration
http://www.royaldevice.com/custom.htm
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Old 7th May 2009, 05:34 PM   #16
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Thanks Per,

Not continuous, about 10 seconds a shot.

BillyDoc
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Old 7th May 2009, 06:00 PM   #17
wg_ski is offline wg_ski  United States
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A 10 second burst certainly wouldn't hurt a Labguppen amp. But its power supply might complain about that long a burst - usually burst testing is done for around 50ms on 120V lines. If it's strapped for 240V operation it may be ok with it (usually input current is limited per safety agency specs).
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Old 7th May 2009, 06:18 PM   #18
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You must have 30 A fuse for 120 V and 16 A for 230 V.
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Old 8th May 2009, 09:16 AM   #19
winny is offline winny  Sweden
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Actually, if you run that amplifier in particular into constant PAL, you will draw 27+ ampere from an 230 V outlet.
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Old 8th May 2009, 06:58 PM   #20
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I have just sent devices out for vibration testing by a lab.
You get a nice Certificate you can pass onto the customer.

But I could see making a quick and dirty tester for small things by just gluing a board to a woofer. Or for larger things, take apart a few woofers and attached the voice coils to a platform at each corner. With a few layers you can get 3 axis shaking. No amp needed as wg_ski points out just pulses.

No sense turning the vibration into sound - there is no sound in space!
Big Bang is a myth - there was no air so nothing to go Bang in.



Yeah I know it's for the launch, but still there will be orbit adjusting rockets and vibration from those in space.
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