Frequency Response Analyzer with Bode Plots

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hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer » Sat Nov 16, 2019 3:22 pm

lech226@gmail.com wrote:
Fri Nov 15, 2019 1:52 am
Hi hexamer.
Thanks for your reply.
I mean. for example:
- Input 1Vpp 1khz -> Vacuum tube amplifier -> 8Vpp output with perfect Sine Wave -> Capture
- Input 1Vpp 15khz -> Vacuum tube amplifier -> 8Vpp output with Sine Wave was cut off the head (not perfect Sine wave output) -> Capture

in the both case, 8Vpp Output capture but the second one is Distortion.
Thank you for the clear explanation. I see what you're talking about. Clipping distortion would result in energy being moved to higher order harmonics in the frequency spectrum. So, a frequency response would only show you is that the gain is limited. As long as the FRA sampling rate is high enough to avoid aliasing-in these higher order harmonics, then they won't show up in the frequency response. This sampling rate can be increased in the settings, but the default is 64x the stimulus frequency.

The only way that the Bode plot would indicate that some distortion may be occuring would be for you to compare the FRA plotted gain to what you think amplifier is set to (within the bandwidth of the tube). For instance, if your amplifier is set to amplify by 10x, and the gain response is lower than 20 dB, then there may be clipping distortion. There are diagnostic tools built into the FRA application that can measure purity of the input and output signals if you wanted an objective number of clipping distortion. But for a first pass to see if there is any distortion, you'd probably be better off using the PicoScope oscilloscope application.

lech226@gmail.com
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Re: Frequency Response Analyzer with Bode Plots

Post by lech226@gmail.com » Mon Nov 18, 2019 1:49 am

Hi Hexamer.
Have a nice day.'Thank you very much for your clear description
I got it.That's is very mean to me.
I would to buy one for my purpose.
Thank you.

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