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How the amplifier works?!
eduardokbb
post Mar 17 2014, 14:51
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Hey there! The topic title is a little stupid, but I kinda know how an amplifier works. The problem I have here is that I don't know what will happen if I have a 500W rms amplifier and connect it with my 150W speakers... It will destroy my speakers or the speakers just take the power they need to work?
Sorry for bad english and dumb question, but I really want to know that because I'm sketching an amplifier and I need to know how to proceed... Thanks!

Peace,
Eduardo Barth.
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pdq
post Mar 17 2014, 14:54
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It is possible that driving a 150 watt speaker with 500 watts could damage it, but much more likely that you will damage your hearing and/or be run out of town by your neighbors first.

So just use a little common sense and you will be OK.
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eduardokbb
post Mar 17 2014, 15:00
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@pdq: Thanks for your attention buddy!

Is there any kind of hardware I can put in my project that can allow me to fix a max output wattage? I mean, my maximum amplification will be 500w, but since I'm using it with a 150w speaker, I set this with some value 'piece of hardware' and it will amplify only 150w (like a volume control)? Thanks!
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Arnold B. Kruege...
post Mar 17 2014, 15:19
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QUOTE (eduardokbb @ Mar 17 2014, 10:00) *
@pdq: Thanks for your attention buddy!

Is there any kind of hardware I can put in my project that can allow me to fix a max output wattage? I mean, my maximum amplification will be 500w, but since I'm using it with a 150w speaker, I set this with some value 'piece of hardware' and it will amplify only 150w (like a volume control)? Thanks!



You can use gain structure to set the maximum possible power that your amplifier will output. This works particularly well with digital sources.

The basic idea is that if your amplifier puts out 500 watts with 2 volts input it will only put out 125 watts with 1 volt input.

If a hidden or at least less accessible volume control is set so that no more than 1 volt ever can reach the amp, you got your power limiter.
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skamp
post Mar 17 2014, 15:34
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Relevant: http://youtu.be/3isQI0nXQRE?t=3m20s


--------------------
See my profile for measurements, tools and recommendations.
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saratoga
post Mar 17 2014, 16:21
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You'll blow your ear drums before the speaker. Just keep the volume reasonable and you will be fine.
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julf
post Mar 17 2014, 16:39
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QUOTE (saratoga @ Mar 17 2014, 16:21) *
You'll blow your ear drums before the speaker.

As someone who has blown several speakers but still has my ear drums sort of intact, I can testify that you *can* blow out your speakers, but you could equally well do it with a 50 W amp.

QUOTE (saratoga @ Mar 17 2014, 16:21) *
Just keep the volume reasonable and you will be fine.

Tell that to the darned guitar player! smile.gif
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DVDdoug
post Mar 17 2014, 18:42
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First, for "normal home listening" I wouldn't worry unless you are having loud parties.

Beyond that, it gets very complicated and there's no solid answer to how much power is safe... Worst case, you could probably burn-out the tweeter in your "150W" speaker with a constant 20W test tone!

JBL has recommendations that run from using a speaker with half the amplifier's power rating for undistorted music to double the amplifier's power rating for highly distorted music.

You can't always trust the speaker manufacturer's power ratings. These are generally just guidelines. Pro speakers are rated per IEC standards, but most home speakers are rated more optimistically.

It's the average power that's related to heat and speaker damage. All music is different, but undistorted music usually has a peak-to-average ratio of around 10:1 or more, and there is more energy in the mid & low frequencies than in the high frequencies. IEC ratings take this into account by specifying test-noise with particular filtering. i.e. A tweeter IEC rated at 100W can handle the high frequency part of the music from a 100W amplifier. (The odds are, the tweeter in your 150W speaker would be IEC rated at less than 150W.)

This post has been edited by DVDdoug: Mar 17 2014, 18:47
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eduardokbb
post Mar 17 2014, 20:24
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Thank you all for the help! Just to clarify, I have a pair of Kef Q300 speakers that, by the price, I guess, aren't high end ones. Their power specs says 120w in the datasheet, it's not even 120w. According to your replies, it probably isn't even 120w. Well, when I finish my sketch and start to build it I'll be back here to tell you how is it going! Thanks and sorry for bad english!

Peace,
Eduardo Barth.
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DVDdoug
post Mar 18 2014, 00:59
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QUOTE
Sorry for bad english and dumb question, but I really want to know that because I'm sketching an amplifier...

...Well, when I finish my sketch and start to build it I'll be back here to tell you how is it going!
Are you "sketching" a schematic for an amplifier you are building?

If you are designing & building an amplifier, I assume you know how to calculate the (approximate) output-power from the DC power supply voltage and the speaker impedance. wink.gif If you are paranoid about burning-out your speakers, you adjust-down the power supply voltage.

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