PA Amplifier power ratings that simply don't add up? - diyAudio
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Old 1st January 2011, 12:36 PM   #1
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Default PA Amplifier power ratings that simply don't add up?

as an example...

Behringer EP4000 Europower Power Amplifier 2 x 1400W | Parts-Express.com

Output power (0.1% THD, both channels driven)
per channel stereo mode:
550 watts RMS @ 8Ω,
950 watts RMS @ 4Ω,
1,250 watts @ 2Ω

Output power (1% THD, sine wave)
bridged mono mode:
1,750 watts RMS @ 8Ω,
2,400 watts RMS @ 4Ω

so, 2400watts rms output or so.

all well and good, but the amplifier runs off 120volts at 15amps, which is 1800watts.

so, 1800watts input, resulting in 2400watts output?

that don't work!
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Old 1st January 2011, 12:52 PM   #2
wahab is offline wahab  Algeria
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They simply assume a 50% duty cycle...
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Old 1st January 2011, 12:53 PM   #3
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Quote:
Originally Posted by wahab View Post
They simply assume a 50% duty cycle...
the specs state sinewave, thats not a 50% duty cycle, and the capacitors in the amplifier would never have enough storage capacity to do that much power even on transients.
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Old 1st January 2011, 01:07 PM   #4
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThyDntWntMusic View Post
the specs state sinewave, thats not a 50% duty cycle, and the capacitors in the amplifier would never have enough storage capacity to do that much power even on transients.
50% on the long term....
A transormer can output easily 50% more than it s rated power.
What count is the mean power delivered over a long period of time.
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Old 1st January 2011, 01:10 PM   #5
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Quote:
Originally Posted by wahab View Post
50% on the long term....
A transormer can output easily 50% more than it s rated power.
What count is the mean power delivered over a long period of time.
but a lot of these amplifiers are class AB amplifiers, using low frequency powersupplies.

meaning the whole setup is only 50% efficient anyway.

so to get 2400watts output, you realistically need close to 5000watts input, from a power outlet, and fuse, thats rated for 1800watts...
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Old 1st January 2011, 01:27 PM   #6
wahab is offline wahab  Algeria
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Total efficency is close to 70% with a low losses supply,
and that seems the case with this one since they claim first
choice toroids..
Anyway, the PS can withstand the overload, provided it is not
of long duration, i.e, more than 20mn/30mn or something like that..
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Old 1st January 2011, 01:36 PM   #7
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Class AB amplifiers are only about 70% efficient at full power, so you can't have an overall efficiency of 70%.

a toroidal transformer is about 90% efficient, but a full wave bridge rectifier is about 80%.

in other words, if you have 1800watts input, you have a potential about 900watts output.

thats an overall efficiency of 50%

Last edited by ThyDntWntMusic; 1st January 2011 at 01:41 PM.
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Old 1st January 2011, 01:50 PM   #8
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Quote:
Originally Posted by ThyDntWntMusic View Post
but a lot of these amplifiers are class AB amplifiers, using low frequency powersupplies.

meaning the whole setup is only 50% efficient anyway.

so to get 2400watts output, you realistically need close to 5000watts input, from a power outlet, and fuse, thats rated for 1800watts...
EP4000 is Class-H, which means with music signals its efficiency is much higher than class-AB. therefore much less current draw than comparable AB.

For sinewave power, for 2500W a class-H will take no more than 3500W from the power outlet.
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Old 1st January 2011, 01:53 PM   #9
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the EPA-2500 is Class H also! and i agree, that 2500 watts is for short duration! maybe a few sine's pulse, or on short burst's or maybe sustained for a few seconds. the specs dont state HOW that is measured. it could be a burst of a single pulse for all we know!
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Old 1st January 2011, 03:47 PM   #10
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThyDntWntMusic View Post
a toroidal transformer is about 90% efficient, but a full wave bridge rectifier is about 80%.
The figure for the bridge rectifier is unrealistic..
This would be equivalent to a 20% voltage drop.
That would be right with a 2 X 3V transfo...
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