Apply sine generator to Ch 1 of amp and take the output of that to the active twin-T filter and then the filter output to channel to X input on the scope (that gives you the distortion products and very little original signal).You can even listen to the filtered output of the device under test to make sure you are making the best adjustments to it.īTW if you aren't going to improve your device under test, the results will only satisfy your curiosity but not improve your system. You are going to have to use some imagination to analyze the result, and you will not get numerical results, but you can use the result to make adjustments to your device under test to minimize the most objectionable distortion. You are going to have to adjust the phase of one of the signals (and likely amplitude too) so that you are measuring (in phase) the input signal against the distortion products (and noise) of the device under test. Get those signals and filters clean.įeed the output of your device under test thru the filter to one channel of your scope in X-Y mode (to get everything except the input signal) and feed the output of your sine generator to the other channel of the scope in X-Y mode. Build a filter for a few needed test frequencies, and for that I'd use a twin-tee circuit in the input path of a high gain op amp and use feedback to sharpen up that filter. Here's my ideas.in tech talk, at low cost, using your brain, rather than a meter. None of them will be a stand-alone, basic, traditional scope. I'm sure a Google search of the usual suppliers of high-quality audio test equipment will yield many options for noise measurement. It's extra stuff that is not usually correlated to the signal (although it sometimes may follow the 'envelope' of the signal). noise is not distortion, in the usual definition of distortion. Generating a THD measurement would require following the concepts presented in the wiki article, assuming it's correct, and additional quality test equipment. Actual measurement (outlined in my last post) is a minefield. It displays a simplified concept of distortion. My answer to your second question is: the method outlined does not measure THD of any level. It is the sum of all fears of distortion. In all my examples, I greatly, greatly simplified the definition of distortion, distilling it to be "not like the original signal."
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