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Old 8th June 2010, 01:11 PM   #1
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Default Power Amplifiers Power Consumption

I am new here.I have noticed that some, or may be all amplifiers manufacturers, I dont knowWrites: Power Conumption: 1300W from the 220VAC lineAnd the power output of that amplifier is 2x 2100W RMS @ 4 OHMSAny explinations?
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Old 8th June 2010, 02:17 PM   #2
wg_ski is offline wg_ski  United States
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Standard test conditions for power consumption in amplifiers is at 1/8 power with pink noise - not full sine wave. It's approximately what the amp draws when playing music with clipping just audible. Expect about 2X that with the amp "blasted". The big pro amps could never get safety agency certification if they had to claim current draw based on the absolute max that you could get on a test bench - and you never see that much for more than a few seconds in any real application anyway.
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Old 8th June 2010, 04:49 PM   #3
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Default power levels

I am not that technical, so excuse my idiot questions! A power amplifier delivers 2000W RMS @ 4OhmsNeeds a power supply capable of delivering 80-0-80 12 Amperes for that channel let say.That means the MAIN power supply, (Transformer, or switching power supply) will draw 1/8 of the OUTPUT power of that amplifier from the mains supply 220VACOr most power amplifiers manufacturers measure amplifiers in peak power only?Or the Main transformer or Switching supply usually dont deliver the REQUIRED power to the amplifier. only peaksThanks
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Old 8th June 2010, 05:59 PM   #4
wg_ski is offline wg_ski  United States
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A 2x2000W/4 ohm amp needs a power supply that is more like +/-140V DC. Such an amp would draw around 40 or 50A off a 220V main with a full power sine wave output (80 to 100A from a 120V main). Try it some time - that's really what they draw if they can produce that kind of power. The breaker on the back panel will trip in a few seconds. It won't hurt a good touring grade amp - but a POS may go up in flames. For current consumption specs, they run the OUTPUT power to 1/8 power (which is typical useage) and see what the mains current is and that's what's reported. Peaks will actually be as high as 40 or 50A on each kick drum hit if it's driven to clipping but the average (or RMS) will be lower. For safety and overcurrent protection, that's the current that "matters". Your A/C may draw 25A when it's cooling and be protected by a 50A breaker. It draws hundreds or thousands of amps each time the compressor starts up (which is why the lights dim).
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Old 8th June 2010, 06:03 PM   #5
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I feel that the 1/8 power spec is false advertising. If an amplifier is rated for 200W then the power draw should be based on delivering that much. This is tantamount to the old IHF music power spec that allowed 2W amplifiers to have a 100W specification.

Industry standard be damned, I won't go with it.
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Old 8th June 2010, 07:56 PM   #6
wg_ski is offline wg_ski  United States
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You're free to build your amps any way you want. The problem isn't with 100W or 200W amps. Those come in under 16A current draw even with a continuous sine wave input. Even the old-school CS800 came in under 20A at full sine and 2 ohms per side. But then amps got "bigger". Double the power, and it takes a 30A feed. Double it again and it's 60A. I guess this made powering 500,000 watt concert systems "impossible" because you've exceeded the substation rating without even plugging in the lighting yet. And the actual current draw was always a small fraction of that. When amps started getting above a kW routinely, the industry decided to rate current consumption based on something that simulated real world usage instead of maximum power.

Unfortunately, what happened next was transformers and heat sinks shrinking to the point where you can't run a modern amp near full power for even 10 or 15 minutes anymore. The argument is always that "you don't need to". The ones that come closest cost thousands. Ones that can't even think about it go for a few hundred bucks.
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Old 8th June 2010, 08:35 PM   #7
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You can reckonon a class AB amp losing 40% of its output power into heat in the heatsinks.
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Old 9th June 2010, 10:45 AM   #8
AndrewT is offline AndrewT  Scotland
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4kW of ClassAB sinewave output power will pull about 25Arms from a 240Vac mains supply.
4000W/ 0.68 = ~5.9kW of input power.
5.9 /240 ~25Arms.

But we all know that a transformer feeding a capacitor input filter does not draw sinewave current from the mains. It draws short spikes of current that flow for only 1% to 10% of the half cycle. The peak of these current spikes is ~ 5 to 10 times the predicted rms current.
I would expect to see current peaks approaching 200Apk from the 240Vac mains supply when the ClassAB amplifier is continuously outputting 4kW of sinewave power.

A two channel 200W into 4ohm ClassAB amplifier would pro rata draw near 20Apk from a 240Vac supply.
We plug these and much more into a 13A BS1363 socket outlet all the time and don't worry about it.
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Old 9th June 2010, 10:55 AM   #9
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Quote:
Originally Posted by bob91343 View Post
I feel that the 1/8 power spec is false advertising. If an amplifier is rated for 200W then the power draw should be based on delivering that much. This is tantamount to the old IHF music power spec that allowed 2W amplifiers to have a 100W specification.

Industry standard be damned, I won't go with it.
Well, to be honest, that 200W amp will never be called upon to deliver that 200W continuously except on the test bench. So the question then is should we spec and built and pay for a test nebch spec or a music reproduction spec?
Be aware if you pay for a 200W continuous capability you pay for something that only the test bencher uses.

jd
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Old 9th June 2010, 11:15 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by janneman View Post
.........and pay for a test nebch spec or a music reproduction spec?
Be aware if you pay for a 200W continuous capability you pay for something that only the test bencher uses.
very obviously correct.

I try to bring listeners/builders back to ground by repeatedly reminding them that the average power output to the speakers should be <= -20dB ref maximum power. i.e. a 200W amp ticks over with a 100mW of output and sounds quite loud with 2W of average output.

This +20dB overhead allows for voltage peaks ~ 10times the average signal level.
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