I've finally got to the point with my tube projects that I'm building pre-amps that theoretically have <0.1% THD. Problem is that my Picoscope 2206 (8-bit scope) doesn't seem to let me measure this low. Even a pure sinewave measures 0.2% THD.
My method for getting a "pure" sinewave is to use the built-in signal generator to produce a 1000Hz sinewave. Then, just to be sure, I pass it through a 2000Hz 2nd order Sallen-Key low pass filter. In the spectrum display I see one spike at 1000Hz. That's it, pure flat from there to the right up to 10Khz. It still shows 0.2% THD.
Is this a fundamental limit of this type of instrument, or am I doing something wrong? If so, what should I be looking for?
My method for getting a "pure" sinewave is to use the built-in signal generator to produce a 1000Hz sinewave. Then, just to be sure, I pass it through a 2000Hz 2nd order Sallen-Key low pass filter. In the spectrum display I see one spike at 1000Hz. That's it, pure flat from there to the right up to 10Khz. It still shows 0.2% THD.
Is this a fundamental limit of this type of instrument, or am I doing something wrong? If so, what should I be looking for?
Computer, software and sound will get you much further. Quite honestly, the 8 bit scope is very limiting.
You would get better results with an older HP 3580 or 3582 spectrum analyzer.
Search this section of the forum for key words: HpW-Works, ARTA, Emu, Focusrite and you will have plenty of info to help you get started.
Also, AudioXpress April 2016 has a great article. You can download from their website for a small cost.
You would get better results with an older HP 3580 or 3582 spectrum analyzer.
Search this section of the forum for key words: HpW-Works, ARTA, Emu, Focusrite and you will have plenty of info to help you get started.
Also, AudioXpress April 2016 has a great article. You can download from their website for a small cost.
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