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Power Output measurement with a scope but no generator
#1
Hi Guys

An oscilloscope is very useful in audio work as it lets you see the quality of the signal passing through what we are building or testing. In most cases, if you own a scope you probably have a sine wave generator as well. However, if you've bought the scope and don't have the generator, you can still see useful things and can still perform a power output test.

A signal source is needed that is audio frequency , such as music or voice. In this case, it does not matter if the signal is continuous or intermittent as long as it is ongoing. use a radio, tape player, CD player, ipod, or whatever has enough signal to drive the amp to clipping.

Connect a bench load - power resistor of appropriate value and wattage - to the amp and connect the scope probe to the output.

Connect the signal source to the input and set the gain or volume to zero.

Turn on the signal source, scope and amplifier.

Dial volume up until you see the wave form clip on both the top and bottom. This does not have to be continuous clipping, just enough that it is easy to see the signal limits on both halves of the wave. measure the peak-to-peak voltage on the scope display, then dial volume to zero.

Divide the voltage reading in half to have peak voltage. You can calculate power, which will be a peak value, then divide in half for continuous power, or, multiply the peak value by root-2 (0.7) and then calculate power for the continuous value.
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