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Old 21st December 2011, 01:24 AM   #1
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Default Output power of an average stereo system?

I have an average stereo system and I need to know how much power it will put out to one speaker (roughly).
I would test it with my multimeter, but I left it at school and it is now break...

So just roughly how many volts and amps are put out by a stereo to 1 speaker.

also, how many volts and amps would be put out by a 20watt guitar amp?

and they both put out ac right?

sorry i know nothing about audio devices...
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Old 21st December 2011, 12:45 PM   #2
amptech is offline amptech  Scotland
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Hello, regarding your question power o/p...it would depend on your hifi...you could check on line for a given amplifier spec....here's one answer...
Say your hifi gave 20 volt ac out put in to 8 ohm speaker it's power would be 50watts...

20(ac volts) divide by 8 = 2.5 amps times this by 20 volts would be 50 watt.. or in to 4 ohm speaker load would be 20volts ac across the 4 ohm load works out at...20 divided by 4 = 5 amp times this by 20 volts out put is 100 watts.

simply use a 8 ohm 100w power resistor and connect it across the amplifier out channel one side at a time.

your 20 watt guitar amp would be roughly 9v ac in to 4 ohms = 20.25 watts... 9v ac divided by 4 ohms = 2.25 amp times by 9 volts ac = 20.25 watts.
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Old 21st December 2011, 12:53 PM   #3
amptech is offline amptech  Scotland
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ignore the so called peak music power out put this is just a sale's thing done to make hifi sound better than it is...the sale's person many say 'oh yes, this peace give's a pmpo of 500watts..you then thing great, I'll buy it right away!! only to get it home plug things up and well, let's just say..your less than pleased with it.. always got for the rms power true power of the item and do some 'home work' on product's before buying them!

them cheap marshall..park..etc 15watt amps sound like a tin pan radio's when cracked full up!
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Old 21st December 2011, 01:00 PM   #4
amptech is offline amptech  Scotland
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remember ac signal in for audio amps and ac volts out! set your meter range to 200v ac and for lower power say set it to 50v ac.
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Old 21st December 2011, 01:40 PM   #5
Mooly is offline Mooly  United Kingdom
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Have a read at these two threads,

So how much power do you really need for domestic listening ?

High efficiency speakers - how much power do they really need?
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Old 21st December 2011, 03:33 PM   #6
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Accurately measuring the output of an amplifier is quite involved. You could simply play some music, measure the voltage across the speaker terminals with your trusty VOM and punch the numbers into a calculator, but this will only yield a very approximate result.

For accurate measurements with a normal multimeter you would need to drive the speaker with a sine wave. Otherwise you would need a true RMS voltmeter.

Then there is the inconvenient fact that the impedance of a loudspeaker varies with frequency. To get around this you need a test load resistor that can handle the output of your amp. Another ugly thing rears it head here. You don't want to do this test for too long because the amp will overheat. The heatsinks on amps are usually only rated for a third of the maximum output.

If you want an idea of the output power of your amp, look at the back panel to see what the mains input power is. The total output to all channels will be some fraction of this - my best guess is one half to two thirds.
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Old 21st December 2011, 03:42 PM   #7
AndrewT is offline AndrewT  Scotland
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Expect an average output from a non clipping amplifier to be between 10mVac and 2000mVac depending on how efficient the speaker that is being driven. Conditions:- normal music in normal domestic surroundings being listened to by normal people with normal hearing.
This excludes drunken parties and adolescents.
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Old 21st December 2011, 03:51 PM   #8
godfrey is offline godfrey  South Africa
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Quote:
Originally Posted by AndrewT View Post
...This excludes drunken parties and adolescents.
He did mention "school" and "break", so I wouldn't rule those out!
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Old 21st December 2011, 04:17 PM   #9
amptech is offline amptech  Scotland
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plasmaninjaa..by reading your post you have a keen interest and what to learn more about thing kind of thing. on this site you will come across so much information that can confuse you, try getting some book's on audio project's or look at rod elliot's audio page to help you.
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Old 21st December 2011, 04:31 PM   #10
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How many beans are there in a tin ?

There are just too many variables that you have omitted from your original post to be able to answer your question sensibly.

The most sensible answer so far is to look at the back of the stereo and see how much power it uses.

Although FAR from accurate, the total music output may be in the order of 50-60% of this figure. It could be far less or marginally more.
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