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Class D Switching Power Amplifiers and Power D/A conversion

AMP1-B: why only 25 watts @8ohms?
AMP1-B: why only 25 watts @8ohms?
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Old 15th August 2005, 06:55 PM   #11
sx881663 is offline sx881663  United States
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Letís look at this a little. If you have 28 volt rails with a non bridged amp this means you have about 26 volts peak before the outputs canít go any further. .707 X 26 = 18.38 volts RMS, 18.38/8ohms = 2.3 amps RMS, 2.3 X 18.38 = 42.27 W RMS. This is a reasonable number as the chip is rated for 100w into 4 ohms. This would be 50w into 8ohms. With a full +/- 30 volts this looks right. These power ratings are at 1% distortion. What this means is a 1% average for the whole sine wave. This in turn means the peaks are probably 10% distorted while the rest of the sine wave is clean. I am guessing here as to actual values but ball park should do. As you noted this kind of clipping is very clearly heard so you probably are stopping when the peaks are only .5 Ė 1% distorted. I would think this could easily drop the power down to the 25w range. It all is a question of when you stop turning the control up. There are way too many variables here to be worried about your results. Just turning it up a little further would be full rated power. Remember a 1db change is about as small as we can reliably hear and 3db sounds only a little bit louder but is twice the power.
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