THD vs frequency

[Lucky-Luka]

Hi all

I've found this link: https://www.audio-perfection.com/au...mplitude-and-frequency-sweeps-in-ltspice.html

I'm trying to understand how to use this script properly.
Can someone tell me how I can plot the THD vs freq graph?
After I've simulated the given example , I went to the error log (CTRL-L) and than I right clicked the log window.
THD vs output amplide graph appear after I select "plot selected meas data"
I have even changed the analyzer_controls.txt commenting the amplitude sweep and uncommenting the freq sweep but the result doesn't change: I cannot display the THD vs freq graph I'm looking for.

If there is another method to achieve a thd vs freq graph using LTSpice it's ok for me.

Happy Holidays.

 

[Lucky-Luka]

No one had the necessity to obtain a thd vs freq graph in LTSpice? Isn't it an interesting info to show? I'm a beginner and I thought it should be displayed.

 

[audioguru]

All audio amplifiers have high frequency phase shift so they need a frequency compensation capacitor to roll-off the high frequencies so that there is no voltage gain at a frequency with enough phase shift to cause the negative feedback to become positive feedback and cause the amplifier to oscillate.
Therefore the open-loop gain of the amplifier is reduced at high frequencies which caused distortion to increase at high frequencies.

You can either see the distortion in a simulation or you can build a prototype and measure the distortion. Sometimes the simulation is wrong.