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Power Output measurement without a scope or generator
Hi Guys

One of the basic tests for a power amplifier is to verify its power output. Ideally, we use a sine wave generator and an oscilloscope, but there are ways to do the test with just an AC voltmeter and bench load - fancy name for a power resistorĀ  Smile

You need a signal source and this is completely noncritical for this form of the test, so just a radio, tape player, CD player, ipod - anything that will provide a signal that is high enough in amplitude to drive the amp to clipping. Signal quality is not important and niether is the actual signal inasmuch as the signal can be music or between-station noise. The only aspect is that it be "continuous" rather than intermittent. The latter would be a person speaking.

Hook up the bench load and the meter set to AC volts across it.

Begin with gain or volume set to zero so you can control what is happening.

Turn on the audio source and the amp, then dial up the volume.

The AC voltmeter will show an increase in level as volume is dialled up, then it will jump a bit and stay steady when the amp is clipping. This is easiest to see on a meter-movement style AVO, but a bar graph on a modern meter will show the same thing. The digital meters will just show that it is counting, or sampling, until the reading is steady at clipping. Take a note of the voltage and dial everything back to zero.

IUse the meter reading and the bench load resistance value calculate the clipped power, thenĀ divide by two for sine wave power.

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