How to measure Wattage of an Amp - diyAudio
 How to measure Wattage of an Amp
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 18th July 2007, 06:33 PM #1 diyAudio Member   Join Date: Jul 2007 How to measure Wattage of an Amp hi i have an old 4 channel amp, i used only 2 channels till now now i have decided to dedicate other 2 channels to a sub can any 1 tell me a simple method to calulate the Rms wattage of my system. i just need an aproximation, i have 2 multimeters, the amp n few 4 ohm speakers a PC with winISD freq. generator with me any great Ideas
 18th July 2007, 07:53 PM #2 diyAudio Member   Join Date: Dec 2004 Location: Jakarta Drive you amp with pure sine wave. If you don't have frequency generator, just use the sound card. You can download the software at http://www.nch.com.au/tonegen/index.html Load the amp with 4 or 8 Ohm high power resistor, or nichrome wire heater Set the multimeter to AC, measure the output of your amp (with power resistor connected). For example, if measured voltage is 15 VAC, (loaded with 4 ohm resistor) then RMS power @4 ohm is 56.25 Watts RMS Power = (V*V) / R_Load = (15*15) / 4 = 56.25
 18th July 2007, 08:22 PM #3 diyAudio Moderator     Join Date: Jun 2004 Location: Georgetown, On One thing to watch out for! Hi darw82, You must use approximately 50 ~120 Hz as a test signal. Unless you are using a good Fluke or new Agilent hand held meter, higher frequencies will be inaccurate. Most digital voltmeters have very poor high frequency response. 1KHz is already out of range for them. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife
 18th July 2007, 08:38 PM #4 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Hi, without a scope to check when the onset of clipping is ocurring, you will need an attenuated output fed to a speaker so you can try to monitor the distortion due to the clipping. Not accurate but it will give a clue. Alternatively, measure the PSU supply voltage and get an estimate from that. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 19th July 2007, 12:09 PM #5 diyAudio Member   Join Date: Jul 2007 thanks a lot hi guys thats a lot i think method is nice enough, i'll try to see if there is any distortion using a Windows oscilloscope in my PC and my MIC will do, thanks a lot all of you, nice and simple idea

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