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  1. #1

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    Default max wattage label???

    I know companies wattage ratings are not real reliable, but I don't understand what the max wattage listed on the back of receivers and amps mean. My Pioneer D812 receiver lists power as 6 channels 100 wpc at 1kHz. This would lead me to believe the amp could put out 600 watts for at least a second at 1 kHz. The back of the receiver list max power of 300 watts. I am using a Fosgate M560 5 channel amp to drive the speakers through the receivers preouts. The Fosgate is listed as 45 wpc. So at 1 kHZ, it should put out a max of 225 watts. The back of the amp list max power as 600 watts. I know the Fosgate is a higher quality amp, but why is there such a huge difference? I will hang up now and listen to the responses. Thanks, Jeff

  2. #2
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    Sales Hype and BS mostly. A lot of manufactures claim some outrageous output ratings that they know are false. The key to buying a good quality receiver or amp is to confirm the power rating is listed as "All Channels Driven."
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    Always remember most amplifiers are only about 60% efficient too. So if you truely have 600 watts of output then the input wattage must be 600 X 1.4. Of course there are a lot of other variables as well.
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    Originally posted by Frank Z
    Sales Hype and BS mostly. A lot of manufactures claim some outrageous output ratings that they know are false. The key to buying a good quality receiver or amp is to confirm the power rating is listed as "All Channels Driven."
    And at 20-20K Hz. Don't fall for the 1K rating, that is where human hearing sensitivity peaks and also where the dB A, B and C scales cross. You want to look for what the full bandwidth rating is.

  5. #5

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    One of the reasons ratings are inconsistent is that they are usually only with one channel driven. Your receiver probably makes 100 watts at 1khz with one channel driven, your fosgate probably makes 5x45wpc with all channels driven, thats the difference in ratings between the two classes of products.

    and just so the kids studying for the SAT don't get mislead

    if X * 60% = 600 watts,
    X=1000 watts, or 600 x 1.667 .

  6. #6

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    This confusion has been going on since the inception of audio it seems. I'll tell you what I know.
    Wattage specification depends on the conditions of measurement. That apart, the wattage of the amp thats written on the rear label is how much current it will need at 120V. (W=V*A that is volts*amperes). These two things are totally different. Now let's look at each of these ratings separately.
    The output of an amp measured under different conditions will be different. The conditions include 1. frequency range of the input 2. length of duration 3. load impedance 4.a particular THD level. Different regulating bodies have tried to standardize measurement conditions....the IEC, DIN and the FTC. At this point of time, FTC ratings are given by most manufacturers. One should understand that there are different amp designs. Depending on the design, an amp may put out 100W RMS from 20 to 20KHz at 8 ohms. But the rating may differ when you compare two 100W RMS amps by giving em an input spike for say 2 milliseconds. One amp might give out 120W and the other 175W. Dynamic headroom (the ability to respond to peaks) should be typically around 2 db in a good amp. An amp that puts out 100W at 1 KHz wont necessarily put out the same wattage from 20 to 20K. Ideally, one should look to see if all channels are driven and the input frequency is at least 20 to 20K when choosing an amp. And the THD level at specified wattage helps to a certain extent.

    Apart from wattage ratings, electrical wattage is totally different. It just shows how much mains power an amp will draw. Different classes of amps have different efficiency. Class A amps have the lowest efficiency. That is why they are bulky with large heat sinks to dissipate all the heat that is lost. Digital amplifiers (class D and T) have relatively good efficiency and so do not need that much mains power as well as heat sinks and bulk. Class AB operation provides relatively good efficiency too. Now, plug in the same equation, W=V*A......remember, an amp might not produce 120 V at the speaker output. Instead, it is going to produce a lower voltage at a higher wattage (more current). What Im saying is, an amp that consumes 100W at 120V may put out 200W at its speaker output.
    I think I got down everything I wanted to say....I hope this helps :)
    Last edited by radkrisdoc; 07-28-2004 at 11:59 PM.

  7. #7

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    Jeff, the first thing is that published wattage ratings are "real reliable", but it has to be known what is actually being rated. The Federal Trade Commission regulation on power amps(16 CFR Part 432)was formulated during the early 1970s when there were very few amps with more than two channels and the requirement that the rated power be supplied for at least five minutes continuously with "all associated channels" driven simultaneously was interpreted to mean two channels. Although multi-channel amps are now common, the language and interpretation of the reg hasn't changed(it's been under study for about four years)and most receiver manufacturers(HK and NAD are two exceptions)continue to rate maximum power with two channels, rather than all channels, driven simultaneously for at least five continuous minutes. The regulation almost certainly will never be amended to require continuous full power for a lengthy time with all channels driven because it's been pointed out that although that situation can be set up and measured in the lab, it would never happen in home use. So, the published power ratings are true, but it has to be understood under what standard the rating is taken.

    So far as the watts number on the back of your 912, 300 isn't the "max power"; it's a measurement of average power use at far less than maximum output(at comfortably loud levels speakers use about one watt, not counting higher peaks). Most receivers have some similar figure and they may help you to estimate your electric bill, but not the maximum power output of the receiver.
    Last edited by John K.; 07-29-2004 at 04:17 AM.

  8. #8

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    Another tidbit with power ratings is the fact that the manufacturers vary their distortion levels(THD%) at the rated/published wattages. This fact is not exactly covered in the FTC document, which is exactly why you will see everybody with a different value, and different THD%.

    A garbage amp could theoretically produce prodigious amounts of power, but at what THD? It may be able to create 300w, but it may be hissing and sound so distorted at that level, that it's useless. That's the problem.

    "Fidelity Firewall" is a much better protocol to use when measuring the output of power amplifiers. The highest amount of amount before audible distortion. Manufactures play with the FTC guidleines, as they are fairly generic, and produce numbers that are often bloated.

    Great information is posted above from the gang.

  9. #9

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    This problem can actually help you weed-out cheesy equipment. If the specs are clear and concise, chances are you have a reputable piece. If the information is vague, and you have difficulty getting a definitive answer, you probably have medicore equipment.

    Source: Squeezebox Touch/CIA Power Supply
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  10. #10

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    The stamp on the back of the unit is the maximum number of watts drawn from your 120v outlet. It has nothing really to do with the amount of watts your receiver puts out. Although, a receiver with a low power requirement, but a high output, is somewhat suspect.

    It's only there to satisfy UL requirements. It simply stats that your receiver can draw up to 300 watts (2.5 amps) of power from your 120v outlet.

    A funny thing though, some older Pioneer 2 channel 100 watt per. receivers are stamped at 500 watts max.

    My Yamaha RX-V2400 has 600 watt (5 amps @ 120v) max on the back.

  11. #11

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    I hate watt rating stickers and advertising, I get tired of explaining why the "770 watt" Sony puts out less power than the "480 watt" Onkyo. However, Onkyo has started jumping on this bandwagon as well. Most of the watt ratings are for 1 channel, at one tone, with a 6ohm load (which most people don't have)for a FRACTION of a second. And they test each speaker, one at a time, then claim 110 x7! rant rant rant....

    One particular Yamaha "100 x 6" receiver only really plays about 37 watts per channel with all channels driven.

    Ugh...

  12. #12

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    is there a way to tell the watts with no manual only what's on the receiver ?

    I have a stereo Sanui and I was thiking of setting up a 2ch but can't tell what the watts are...

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