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Hmmmmm....

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  • Hmmmmm....

    I'm looking at purchasing a local used Crown XLS 1000 off Craigslist and was looking at the pics of the rear of it. For the power input, it shows 175w above the power cord. This amp is rated for:

    215 watts x 2 (8 ohms)
    350 watts x 2 (4 ohms)
    550 watts x 2 (2 ohms)
    Output power, bridged mono mode (EIA 1 kHz): 700 watts x 1 (8 ohms), 1,100 watts x 1 (4 ohms)

    With those specs, why do they put a 175w rating for the input? I also looked up another similar amp, the Behringer inuke NU1000, and it has a 150w rating by the power cord input. I know for sure the NU1000 does way more power than that:

    https://www.youtube.com/watch?v=Ibsvu1xownw

    So, why do they do it?
    Attached Files

  • #2
    The Crowns have been tested to deliver rated power. It's likely an RMS power rating for power purposes/duty cycling. The DSP amps from PE are rated at like 50W for the 250DSP and 500DSP.
    Transient power developed will hit rated levels, but a majority of the power supplied should not likely consume more than the plug rating.

    Later,
    Wolf
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
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    • #3
      It goes to show you the games they play to get those ratings.
      Guess xmax's age.

      My guess: 15. His grammar is passable. His trolling is good.

      Comment


      • #4
        Music isn't sine waves it's usually a LOT more dynamic so an amplifier output power rating will never be equal to input power consumption.
        But an amp can't be more than 100% efficient right?
        Right, but the standard for rating an appliance is based on the continuous (average or RMS) amperage draw under a typical load. Problem is the typical load an amp sees varies with frequency and the number of drivers attached but the rating agency wants a single number to use so they base it on the average continuous current draw under AES test signal conditions which produces a very low number these days.
        Paul O

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        • #5
          The reason it's marked as 175 watts is because that's how much power it consumes at 1/8 power using pink noise, the manual is your friend......

          Comment


          • #6
            Originally posted by devnull View Post
            The reason it's marked as 175 watts is because that's how much power it consumes at 1/8 power using pink noise, the manual is your friend......
            Yup. As has been noted in other posts, music has huge peaks (sometimes >20dB). Run the amp much past 1/8 power average, and you're almost certainly clipping those peaks off.
            Francis

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            • #7
              I always thought that was power consumption and nothing to do with output wattage. My Soundcraftsmen MA 5002 is rated at 250W into 8ohms but on the back by power cord it says
              120v 9A/1,000watt max. It is a class H amp where the newer Crown and I nuke are class D which I believe takes less current to achieve the output wattage. I could be wrong but
              I did stay in a Holiday Inn last night.

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              • #8
                Well, they could rate the amp any number of ways. Since the manual says 1/8 power with pink noise, that's their answer. I suppose if you used the amp in a lab (for example) at full power into a resistor or whatever, it has to draw more power.
                Francis

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                • #9
                  Originally posted by Squidspeak View Post
                  I always thought that was power consumption and nothing to do with output wattage. My Soundcraftsmen MA 5002 is rated at 250W into 8ohms but on the back by power cord it says
                  120v 9A/1,000watt max. It is a class H amp where the newer Crown and I nuke are class D which I believe takes less current to achieve the output wattage. I could be wrong but
                  I did stay in a Holiday Inn last night.
                  Backplate label is the power consumption of the amp. It does have a relationship to the output wattage and how the manufacturer has rated the amp. At idle the amp draws some power just because it's on. As the output goes up the power used goes up. In the case of your Soundcraftsman, making a couple of assumptions, it's relatively easy to see how they came up with the 9amp rating on the label. Now for some math.

                  It's rated at 250w RMS at 8ohms. 360w at 4ohms. So we use linear extrapolation and come up with a 2ohm, which the sales brochure said it was capable of driving, rating of about 400w. So we double the 400 watts and get 800 watts continuous RMS power for 2 channels. So the amp is a class H which is a class AB amp with switching rails. Figure about 75% best case efficiency. So 800 / .75 is 1066 watts consumed. 1066/120v is 8.8 amps. Pretty close to the 9amps on the label.

                  So we can make a pretty educated guess that Soundcraftsman did the nameplate power consumption using a constant sine wave, 1KHz, at full RMS power into a 2 ohm load. Remember that this is a home amp so it needs to be specd according to the FTC rules. The Crown is considered a professional amp so it doesn't need to conform to standardized testing, it's up to Crown to decide how to spec the amp.

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