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How do I measure peak watts, amps and volts?

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Posted on November 28, 2015 at 19:14:37
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
 I don't listen to loud music. I also have a small room. I listen to chamber music 95% of the time. So, I am trying o determine how many amps, volts and watts I am using. So, How do I determine how many peak watts I am using? Amps? Volts? How do I measure such things?

 

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RE: How do I measure peak watts, amps and volts?, posted on November 28, 2015 at 20:32:57
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 Basically
1. Get a nice True RMS Meter
2. Get a sine wave generator
3. Get an Oscilloscope
4. Get a dummy load of 4 or 8 ohms

Put in the dummy load for the test instead of a speaker.
Hook up the sinusoidal signal generator set to your favorite frequency (1K is the standard)
Put the sin wave through the amp.
Measure the voltage across the dummy load.
View the output signal on your oscilloscope and look for when the sin wave starts to deform. Back down the signal until it is pure again, that is your max power.
Measure the voltage across the dummy load and use the old W = V^2/R if you have a true RMS measurement. (If you measure 10 volts true RMS and have a 8 ohm load the calculation would be 100/8 or 12.5 Watts.

That will get you somewhere close to a actual power output in watts.

Or, try a low power amp with the speakers and see if you are OK with the output.

 

RE: How do I measure peak watts, amps and volts?, posted on November 28, 2015 at 21:46:32
Triode_Kingdom
Audiophile

Posts: 10049
Location: Central Texas
Joined: September 24, 2006
 It's difficult to analyze this with much accuracy using simple equipment. However, an oscilloscope will give you an approximate indication. Just set system volume to the listening level you normally use, then measure the peak voltage across one of the speakers using the scope. Use the formula "(voltage squared)/R" (R equals nominal speaker impedance) to determine the peak power delivery. Again, this will be approximate, but it will give you a pretty good idea of the power you're using.


 

RE: How do I measure peak watts, amps and volts?, posted on November 28, 2015 at 22:57:02
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 Simplest is to get a meter with a peak hold function. I googled [voltmeter "peak hold"] and found this:

 

RE: How do I measure peak watts, amps and volts?, posted on November 29, 2015 at 05:59:54
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
 Thanks everyone. This is exactly what I needed.

 

RE: How do I measure peak watts, amps and volts?, posted on November 29, 2015 at 08:56:17
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 You could record some music from the speaker terminals with a program like audacity and then go back and analyze the results. The typical input limit is 1V peak so you would need to do a voltage divider to pad the level down. Depending on how much power you expect you could use a 1K and 10 ohm resistor and then multiply your results by 100. (990 ohms and 10 is exact) If you are expecting less than 8W then you could go for 910 ohms and 100 for a value of 1/10th of what you record. I would just make sure that the divider more than 100X the speaker load.

If you really want to have fun, you can then take the .wav file and run it in LTspice to analyze it some more. Here is the cannon fire of the 1812 and you can see that the file is clipping the 2V p-p scale for what one would consider to be a .7V rms output. When you analyze it in spice, it calculates a .25V rms output which makes me wonder what value sine waves and RMS actually have in audio.





Here is the FFT of the above clip which shows hoe the cannon fire breaks down into frequencies.





I have looked at about 20 different things in the search of large amounts of bass information and short of some electronic music where they do it on purpose, this grab of the 1812 was the worst I could find. By no means was it an extensive search but I am open to any pointers to some real bass heavy music.

dave

 

Sine waves and audio, posted on November 29, 2015 at 15:12:36
Chip647
Audiophile

Posts: 2653
Location: The South
Joined: December 24, 2012
 You are right, there is not much in common for audio, but "Watts" is a power calculation that uses RMS and Sine waves. If you go with Peak voltage, you need to use the V^2 / 2R formula. But when measuring the speakers with music, the "R" is very hard to get for a random music peak at a random frequency. Jeffrey once explained to me the futility of this form of measurement.

You don't want to start the "my 2A3 amp puts out more power than your 100 watt amp because of the magic transfer function...." Tube amps have overhead that solid state does not have from the tubes themselves and the magnetics.

A full signal from a CD is no different than a half signal. The only thing that makes 1812 so impactful is that most of the program is well below peak, so that when the peak hits it is comparatively very loud, but a 2 volt signal is a 2 volt signal.

 

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