power ratings rear panel

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cameron999

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#195988 14-May-2016 20:35

hey, do the power ratings on amplifiers on the rear panel tell us much?

a yahamah amp boasting 85w per channel 8ohms with 220watts on back panel

pioneer boasting 60w per channel 8 ohms with 500watts on rear panel

both 2 channel amps.

can anyone help me with this?

richms

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#1552789 14-May-2016 20:51

They tell you nothing, just like the power rating they have on the box means nothing as it is a meaningless figure without all the other specifications that happened when it was measured.

Richard rich.ms

Dunnersfella

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#1553055 15-May-2016 14:28

What Yamaha stereo amp has 85W per channel? I thought it went 60W, 80W and 100W (8ohms / 20Hz-20kHz : 0.06%THD)?

As an aside, class D amps are even more confusing...

Technofreak

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#1553079 15-May-2016 15:12

The figures you quote don't mean a lot without references to how they were obtained.

The 220 watt and 500 watt figures I suspect relate to the the power consumption of the unit and bear no relation to the audio power output.

The audio power output figures need more information to be meaning full. e.g. Are they peak or RMS measurements?

While not an exact analogy I liken quoted audio power figures to those quoted for cars. The same engine will have two different kW figures for SAE and DIN.

Remember also for the human ear to be able to hear the difference the power output needs to double. You will not notice any volume difference between 60 watts and 85 watts. However, provided the speakers are up to it, there will likely be less distortion from a 85 watt amp that's only producing 60 watts than a 60 watt amp at 60 watts.

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blakamin

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#1553080 15-May-2016 15:15

I'd be agreeing with @Technofreak that the numbers on the back are the power supply rating.

cameron999

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#1553296 15-May-2016 20:01

i might have been confused with the yamaha specs, have looked at so many latley, the only specs i look at are the 20-20khz at 8ohms.

Technofreak

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#1553322 15-May-2016 21:42

cameron999:

i might have been confused with the yamaha specs, have looked at so many latley, the only specs i look at are the 20-20khz at 8ohms.

You just need to find out whether they're quoting Peak or RMS or any other standard. Unfortunately not all manufacturers use the same standard. About all you can assume is the same standard is used by each manufacturer for all of their products. Yamaha is a pretty good brand.

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tripper1000

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#1553368 16-May-2016 00:50

The guys above are right in your particular context.

IMHO, the THD % is the most important figure when comparing one amps power rating to another. As a very general rule, the human ear will notice distortion over 0.1% so distortion ratings above this are dishonest.

As an example, my current Denon (40 watts RMS per channel) kicks the ass of my old Sony (135 watts RMS per channel) on the same speakers. The difference between them is that the Denon is rated at 40 WRMS @ 0.1% THD and the Sony is rated at 135 WRMS @ 5% THD. 5% THD is total useless for listening to and may as well be 100% distortion. When you followed the Sony's distortion graph down to 0.1% it is producing around 20 watts RMS, hence the Denon sounded much cleaner and clearer at higher volumes.

One thing the power supply rating is good for is spotting and calling B.S. on the amp output ratings. The combined outputs of the amp can never exceed the power supply rating, without breaking the laws of physics, other wise the amp would be creating energy - which is of course impossible. For instance, if the amp alleged to be 5x 100 watts RMS, but the power supply is rated at 250 watts you can instantly spot that there is no way that the amp rating is true, because there would be another 250 watts coming out of thin air, and that is before you even consider heat losses and inefficiency.