How do I know real wattage

Discussion in 'Archived Threads 2001-2004' started by MikeMcGrew, Jan 12, 2003.

  1. MikeMcGrew

    MikeMcGrew Stunt Coordinator

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    I am considering a new receiver for my HT and music but everyone I talk to says the "Watts per Channel" spec quoted by the manufacturer is a bogus number. My older Pioneer VSX-D508 states 100WPC. The power consumption number in the back of the manual reads 280W. Do I divide this number by the number of channels or what? For example: If I am watching a DVD in 5.1, do I divide the 280 watts by five? By six? What about 2 channel music? Divide by two? I apologize if this is a basic question but I'd like to know what to expect from a receiver. Is it true that I should "buy by the weight(actual pounds) of the receiver???
     
  2. MikeMcGrew

    MikeMcGrew Stunt Coordinator

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    All I'm really asking is how do I know what kind of current my receiver is actually pulling and how do I measure this. Any help would be appreciated. Thanks. Mike
     
  3. Mat_M

    Mat_M Stunt Coordinator

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    This is a good question and I'm guessing many others would like to know a solid answer also. Here's something to add to the confusion...I have a Harmon Kardon AVR300, which is rated at 50W per channel in 5.1 mode. The .1 channel is only a line level output, so it's power is minimal. This would leave 250W of power delivered, yet the manual states that its output is somewhere near 670W when all channels are driven. Does this mean I'm loosing 420W to heat?!? I'd hope not. Someone who's an expert on this please chime in.

    Mat
     
  4. Brae

    Brae Supporting Actor

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    You could buy some 100W or 200W dummy speaker loads (giant power resistors) from PartsExpress and measure the current going through these dummy loads.
     
  5. Andrew Pratt

    Andrew Pratt Producer

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    The easiest way to find out how an amp or receiver does is to find a credible review. Sound and Vision tends to post bench scores for the models they test as do most AV mags.
    Of course there's always this page that has a lot of them listed for you
     
  6. Mat_M

    Mat_M Stunt Coordinator

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    All I can say is (if in fact it's accurate): That chart is just plain beautiful. So in some cases we're seeing actual power output higher than rated, and in others lower than rated. Interesting. Now I'm curious as to what equipment they used to make the data...
     
  7. MikeMcGrew

    MikeMcGrew Stunt Coordinator

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    Thank's for the link Andrew. Anyone else have links like this one? Especially for newer receivers.
     
  8. DarrylM

    DarrylM Stunt Coordinator

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    It is all very confusing. There are a couple of things to look for though, which can help you make the right decision.
    Believe it or not, the Federal Trade Commission places several restrictions on how manufacturers can advertise amplifier power. Unfortunately, these restrictions simply require manufacturers to describe how their amplifiers are rated, which leaves them with a great deal of flexibility. Consequently, a manufacturer can make some pretty dramatic claims about performance by simply selecting criteria that are easy to meet for rating their receivers.

    Let's consider a practical example to illustrate some of the subtle details to look for when shopping for receivers based upon power, alone. Brand A and Brand B both advertise 100 W x 5 on a little sticker on the faceplate in the local electronics outlet. Same power, right? But Brand B costs $200 more, so you opt for Brand A, which has the same features. But that little sticker on the faceplate (or shelf placard or box lid or whatever) is pretty ambiguous. What does 100 W x 5 really mean? A look at the specifications in the manual can reveal the true performance.

    Brand A is rated at 100 W in stereo at a 1 kHz test tone with less than 0.7% total harmonic distortion. This might look like so in the manual:

    100 W x 2 @ 1 kHz with
     
  9. Paul Stiles

    Paul Stiles Agent

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    Only by being one with the volts and amps will you be able to know real wattage.

    -zen EE master

    Paul
     
  10. Philip_T

    Philip_T Supporting Actor

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    Great post DarrylM [​IMG] . That actually made sense to me and my limited knowledge of electronics! This was one of those topoics Ive always wondered about, but never got around to asking.
    Regards,
    Phil
     
  11. Iver

    Iver Second Unit

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    One way to get a general idea of the actual power output capability of a receiver is to note its rated amperage draw.

    For example, my Denon AVR-1602 is rated as drawing 3.7 amps (at the standard wall current voltage of 120).

    This gives the receiver a rated power consumption of 444 watts (volts times amps equals watts).

    Meanwhile, Denon claims an output of 70 watts, into eight ohms, per channel (x5), or a peak output of 350 watts.

    Of course, not every watt that goes into the receiver becomes output power. A small amount of it powers all the stages other than the final output transistors. And then some is lost to the inefficiency of the amp, turned into heat.

    The bottom line is, there is reason to believe Denon is more or less telling the truth about the power output at the eight-ohm rating.

    On the other hand, Denon claims 100 watts output into six ohms, albeit at higher distortion and only measured at 1 kHz rather than across a frequency spectrum.

    That would require consumption of over 500 watts, which would be well in excess of the receiver's rated current draw.

    Oddly enough, some of the pictures of new receivers on Denon's Web site have the amperage figure on the back of the case blacked over.

    Realistically, there's not much software which will cause all five amplifiers to simultaneously output their maximum power. In movie soundtracks, there are long periods where the surround channels are almost silent.

    Most of the time, the main channels of a receiver probably put out five watts or less, unless you are really cranking it.

    In any case, rated amperage is a significant number and gives you an idea of how close a relationship exists between what the manufacturer claims and what the receiver is ulimately capable of putting out.

    As for your question about weight, I would say that this figure is also fairly significant. Things like hefty transformers, adequately large heat sinks, and solidly-built cases all make great contributions to a receiver's weight. So, in a sense, with all other factors equal or almost equal, the heavier of two receivers would tend to put out more power and/or have a more solid build.

    It's not like you should eliminate one of two receivers because it weighs two ounces less than a competing, similarly priced model, but a difference of two pounds is something to consider.
     
  12. MikeMcGrew

    MikeMcGrew Stunt Coordinator

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    AAhhh Math, now that is something that I can get behind. I really appreciate the responses. I have learned a lot from this post. Thanks again. I am going to do some reading this week and see if I can come up with some manufacturers that are somewhat honest and consistant about what they report to the consumer. So far, it seems that Onkyo and Harmon Kardon are pretty well regarded. As always though, they are also more expensive. Referring to that chart that A. Pratt linked earlier, you see brands like Sony and Kenwood that are claiming 100+ WPC and only delivering 30 or so. That really disappoints me as a consumer. I am no expert but I at least take the time to learn a thing or two before I buy. I wish more consumers would do the same, then we wouldn't have to deal with companies like B_ _ _.
     
  13. AaronBatiuk

    AaronBatiuk Second Unit

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  14. Iver

    Iver Second Unit

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  15. AaronBatiuk

    AaronBatiuk Second Unit

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