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Old 23rd March 2005, 10:18 AM   #1
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Default power output higher than power supply...How?

Hi,

My Audio Engineering teacher told us (in 2002) that you can power a 5000W PA from a 2400W (240V 10A) power point. How does this work?

I also looked for that old thread where Nelson Pass explains concepts like this but I've been looking for days, and I can't find it!

Thanks, from Steve.
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Old 23rd March 2005, 10:41 AM   #2
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Interesting knowledge but somebody has misunderstood things I'm afraid.

If you consider this: You are taking out 2400 watts which flows into a magical box and out of this box you can take out 5000 watts.

But... if you have 3 x 240 V three phase you can take out 7200 W and with a class D amp I think it's quite possibe to get 5000 watts.
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Old 23rd March 2005, 11:04 AM   #3
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I guess he was just referring to the fact that music and speech have a lot less energy content than a sine wave, so a system that is rated at 5kW sine wave, when used (up to the point of just clipping) with music or speech will take less than 5kW from the supply.
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Old 23rd March 2005, 04:29 PM   #4
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More :
no amplifier will just do 1 frequency at full power.
Any audio signal will consist of a number of frequencies, the spectrum has different energy levels for each of the frequencies.
Total energy from that spectrum will be far less than the maximum output.
Nobody in his right mind will try to feed only a 1KHz tone to an amplifier at full power for extended periods, unless he is a welder.
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Old 23rd March 2005, 04:34 PM   #5
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Come now, Jacco, some of us like the idea of an amplifier being able to do that sort of thing. Some also like to design for the ability to have shorted outputs cause no harm at all, by way of high current capability. Of course, then some call both of these:

Overkill!
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Old 23rd March 2005, 06:07 PM   #6
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Well perhaps he meant 5kW for very brief moments not constant... after all Caps can hold a lot of juice!
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Old 23rd March 2005, 06:49 PM   #7
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The only amplifier i heard of that can do that is the ML20.
But hey, why not build us a couple, i am game !
Just recently Mr Hugh Dean called me an excessive European, a contradiction in terms.
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Old 23rd March 2005, 09:35 PM   #8
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Manufacturers of modern computer speakers have discovered how to get more power out than the supply going in, by a factor of about 1000:1. I have a pair of 120 Watt amplified speakers and they run on a 2 watt wall wart with thin, thin copper wire supplying the amp.

At 12 volts it would take 10 amps of current to make 120 watts, yet the wire stays stone cold as though it were only carrying about 160 milliamps. Clever engineering here for sure!

Home theatre amp manufacturers have discovered the same secret. You get six channels, each producing 100 watts (says so in writing!) and the whole box only draws 100 watts from the mains. This used to be called impossible.

Why don't they use this technology for the new electric cars? Any car employing this same technology could easily have an engine with at least 500 horesepower, even more! The motor could be very small as it doesn't have to handle but a small fraction of that much power. Since it would be very light weight you could drive 1000 miles on a disposable D cell battery.

I'm afraid the only thing they have achieved is to make devices deliberately so worthless (Black Plastic ****) that you cannot repair them if you wanted to. You throw the junk away and buy a new one.

Now, taking tongue out of depression in cheek, Loonatron, what your teacher probably meant was that because the power distribution in audio makes the average power but a small fraction of the peak power, a smaller continuously rated power supply that had sufficient energy storage capacity to handle the peaks (capacitors), could run a system with far greater rated peak power output than it's own continuous input feed. That is not magic. It is like having a power supply that can only light a 1 watt lamp. If you use that power to charge a car battery (for example) for 100 seconds (forgetting about inefficiencies of batteries for the moment), then you could fully illuminate a 100 watt light bulb (but for only 1 second).
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Old 24th March 2005, 10:47 AM   #9
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Thanks for those replies!

Peranders... I see your logic, but he was definately talking about single phase.

Everyone else... Yeah, he must have been talking about peaks, unless he made a mistake!

rcavictim... That's really funny! Yes manufacturers have made great advancements in recent years, especially in the field of physics-bending!

jacco... I will have to read about this ML20.

Now does anyone remember this heated discussion about Nelson Pass's specs? It was an interesting read, I want to re-read it but I can't find it!
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Old 24th March 2005, 07:04 PM   #10
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I'll guess you have to ask your teacher to explain in detail his claim or theory. I'll guess this wasn't the first time a teacher has misundertood things and then "teach" his poor pupils....
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