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Overrated amps

Joe Peeps

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Ok, so I stumbled across this thread by 12 volt King and did some maths…

http://forums.justcommodores.com.au/showthread.php?t=14914&highlight=amp+power+ratings

My Audiobahn 4002T amp is rated as producing 400 RMS bridged across the 2 channels.
It has a 40amp fuse, so Applying the relevant formula,

Power = 40 x 14.4
= 576 RMS at 100% efficiency

400/576 = 69.4% efficiency required to produce the touted power.
Correct me if I’m wrong, but I read somewhere that the theoretical max efficiency of a class A/B amp is 66% i.e. this amp can never reach the advertised level of power.

Leaving aside that +/- 50wRMS is no big deal in real terms, and that differences will always occur during manufacture, I have a real problem with the advertising of ratings that are physically impossible and can never be attained.

Before I fire off an abusive email demanding my money back (I bought the amp before I found this and other forums) have I overlooked any important info? Otherwise id be left looking quite the fool….

Cheers
 

Tasmaniak

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the only important info I can give you is that all amplifiers are either over or under rated.

With that aside....you will probably find that your amp probably goes well over that 400watts point hundreds and hundreds of times. Because it is 400wrms, that doesn't mean it can't produce more then that. wrms simply means all day running power. Or a constant power output. You will find that your amp has probably spiked well over 1000watts. But only for a fraction of a second.
 

Joe Peeps

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Ok, thanks mate. I guess i'll keep my email to myself then...
Just to clarify, although it can spike well over the "400" mark without blowing the fuse, i still dont see how it can run 400 as advertised - 1x 400RMS (or as a constant power output as you put it)

Thanks
 

azzfox

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im not sure what your trying to ask there, but if this helps, 400wrms is what it hangs around constantly give or take a bit. 40amps is the maximum it will draw and shouldnt exceed this. and if it slightly spikes over this it will happen so quickly the fuse will not blow.
 

Joe Peeps

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Cheers fox, What Im trying to establish is how the amp can be rated at 400RMS - which as you put it means that the output is constantly at this point give or take. I understand there will be peaks well over this but if you look at the efficiency required given both the fuse rating and battery voltage to produce the given 400wRMS continuously, then it would require the amp to be 70%efficient which is impossible for a class A/B amp.

My general point is that it is surely a breach of the TPA for manufacturers to quote figures that are unnattainable -and i dont mean through peaks, but continuously, which is what i thought the RMS rating was - continuous!
 
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