measuring amp output

[gcmarshall]

what does it take (ie, what kind of equipment, etc.) for one to measure actual wattage output from an amplifier? for example, if i wanted to measure the actual performance of my amps to see what kind of output i am acutally getting, is that something that one can do with inexpensive equipment and simple formulas or does it really call for advanced equipment and detailed knowledge of certain things? i am guessing it takes some serious measurement capabilities, such as is done on sites like this when they measure output for receivers, for example. but, just curious if this is something one can do with relatively little cost and experience.

i'd like to know what the actual output is for my audiosource amp one/a running in bridged mode to see if one actually gets anywhere near the claimed 200 watt/channel.

 

[xboxweasel]

If you can clamp an ampere meter on one of the wires feeding your equipment then you can get a current reading. Clamping around a cable will get you a net 0 amps. One method is to take an extension cable and cut back the outer insulation layer exposing the 3 separately insulated wires underneath. Typically these will be coloured black, white, and green. Clamp on either the black or white wire. The green wire is ground and you will not get a reading.

Or you can use an inline ampere meter. This would require cutting into either the black or white wire. It is a little more risky, since you can get a shock if you are not careful.

Power (watts) = volts x amps
Volts is 120VAC, unless you live in Europe, then it would be 220VAC. Amps are what you are measuring.

This will give you a rough idea.

 

[MacManNM]

If you can clamp an ampere meter on one of the wires feeding your equipment then you can get a current reading. Clamping around a cable will get you a net 0 amps. One method is to take an extension cable and cut back the outer insulation layer exposing the 3 separately insulated wires underneath. Typically these will be coloured black, white, and green. Clamp on either the black or white wire. The green wire is ground and you will not get a reading.

Or you can use an inline ampere meter. This would require cutting into either the black or white wire. It is a little more risky, since you can get a shock if you are not careful.

Power (watts) = volts x amps
Volts is 120VAC, unless you live in Europe, then it would be 220VAC. Amps are what you are measuring.

This will give you a rough idea.

HUH?

Unless you are going to run a 60Hz test tone into your system this isn't going to give you anything. Your best bet would be to use resistance and volts but since the speaker impedance changes the calculation is worthless.

To perform this measurement in some sort of quasi correct fashon, you need 3 things
1. Signal generator
2. O'scope or true RMS power meter
3. A resistive load, not reactive like speakers.

With this simple set of diagnostics you can in fact get much more than just power.

 

[xboxweasel]

i'd like to know what the actual output is for my audiosource amp one/a running in bridged mode to see if one actually gets anywhere near the claimed 200 watt/channel.

I am not saying I disagree with you. And I am saying I am not an expert in this field. I don't know much about speakers and their power requirements. I do know their impedances change with frequency, therefore changing power consumption. It would also be difficult to get a reading while listening to music or movie soundtracks.

However, I understood that GCMarchall was asking how much power his equipment consumed while being used. It was just for a rough idea. And how many people have signal generators and oscilloscopes?

 

[MacManNM]

I am not saying I disagree with you. And I am saying I am not an expert in this field. I don't know much about speakers and their power requirements. I do know their impedances change with frequency, therefore changing power consumption. It would also be difficult to get a reading while listening to music or movie soundtracks.
However, I understood that GCMarchall was asking how much power his equipment consumed while being used.

He actually wanted to know what the output was. No biggie, we were talking apples and oranges there, I just didn't want someone to try and put a current meter on their speaker wire and try to get a real reading!

It was just for a rough idea. And how many people have signal generators and oscilloscopes?

I do! Tons of both.

 

[xboxweasel]

I just didn't want someone to try and put a current meter on their speaker wire and try to get a real reading!

I was refering to the cable feeding his amp. To get a current reading on it. To get a reading on the speaker itself would be difficult. Most multimeters, clamp-on meters only work at 60Hz.

I do! Tons of both.

You sound like my buddy Bill. He knows a lot about this stuff. I should visit him sometime.

 

[gcmarshall]

guys-

thanks for the input and suggestions. in short, it sounds like something i am not prepared or trained to measure. so, unless the reviewers on this forum would perhaps like to do a review of "budget" amps, such as the audiosurce amp one/a, (which might not be a bad idea since people always like to save money if they can find a good performer for not a lot of money), i will probably not pursue doing a test myself, since i would probably end up doing something stupid.

happy new year to all...

 

[MacManNM]

Radio shack used to make a little power meter that ran in parallel to your speakers. They were pretty accurate (within a factor of 2 or so), plus they looked cool. Im sure you can find one on ebay for ~$10 or so.

 

[W_Harding]

guys-

thanks for the input and suggestions. in short, it sounds like something i am not prepared or trained to measure. so, unless the reviewers on this forum would perhaps like to do a review of "budget" amps, such as the audiosurce amp one/a, (which might not be a bad idea since people always like to save money if they can find a good performer for not a lot of money), i will probably not pursue doing a test myself, since i would probably end up doing something stupid.

happy new year to all...

MacManNM is correct about the equipment needed to perform an amplifier output power test. I have done this many times on many different amplifiers. An easier and less expensive way for you to find out how much power your amplifier puts out would be to pay a service shop to make the test for you and let you watch. Any good service shop has this equipment and any service technician would know how to measure the power output.

 

[PENG]

MacManNM is correct about the equipment needed to perform an amplifier output power test. I have done this many times on many different amplifiers. An easier and less expensive way for you to find out how much power your amplifier puts out would be to pay a service shop to make the test for you and let you watch. Any good service shop has this equipment and any service technician would know how to measure the power output.

Xbox is not totally wrong if he meant measuring power consumed by the amp, except that people keeping forgetting Power=VI is only true for purely resistive load.

For reactive load (loudspeakers are), Power=VI cos θ
θ is the phase angle between the V and I phasors, and cos θ is know as the power factor In this case, I believe cos θ will be less than 0.8. Using Xbox's method, if you assume power factor (cos θ) = 0.75 on average, and efficiency = 0.6, the output from the amp will be roughly 0.45, of 45% of the measured (current), and then calculated (using the formula above) value of power draw from the wall outlet.

If you can accept such approximation, at least one problem remains, the power draw will vary greatly with the source material, classical music probably will be worse and rock music the best. If that's not good enough, then go the MacManNM route.

 

[W_Harding]

The original question was =>

what does it take (ie, what kind of equipment, etc.) for one to measure actual wattage output from an amplifier?

The origninal question was not, how much power does the amplifier draw from the line when playing music? gcmarshall seemed to what to know if the amplifier when bridged was able to deliver the power claimed by the manufacturer. To test the amplifiers capability the equipment suggested by MacManNM will do the trick. To measure an amplifiers output power capability is a simple and straightforward measurement if one has the equipment.