Excellent 
Btw, what kind of attenuator are you using there? Iām sure you remember me trying to make my own in that other thread.
Here is the Load/ attenuator I am using for my Left channel. I tried to label the important things. Originally, I was taking the attenuated output across the 0.1ohm resistor (green), but even at 200w there was not enough signal Matt pointed out. I added another banana terminal across the āoutputā of the very first 2ohm resistor, which gives me 12.3dB attenuation, which is good for at least 400w- the max I will ever measure (at least for now). I could probably take the 0.1ohm resistor out but it is not worth the effort makes little difference overall. When I am measuring smaller amps I just move the cable that is at the āoutputā of the 2ohm resistor to the Amp - banana jack (black) and set the ext gain in the software to 0. My right channel is set up pretty much the same way except I used eight, 1 ohm 50w resistors and measure across the 2nd resistor from the + amp input (I built that load a ways back). I will probably insulate the black āmounting bracketā or BNC connector as I accidently shorted out a lead to the heatsink:
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@ Matt:
What do you think about this THD compensation approach?
Is it something that could be implemented on the QA402?
Just found it interestingā¦
Ah, so you use a combined load and attenuator, in a similar fashion to what Matt wrote about on the blog. Looks very handy!
I could not be w/out my load/ attenuators. May build one for 4ohm loads at some point. I will be using one of them today to calibrate an arduino nano LED power meter that I designed and built to measure 350w. IT is much easier to do using a QA402 than an Oscope!
In .9999 the folder location where the .png file for āSave as Bitmapā when using the AmpFreqRespChirp plugin does not appeared to be remembered after first time one is savedā¦
Some work was done in that area when phofman first outlined the technique and I posted a summary on DIY audio in 2019. The cancellation technique of pre-distorting is well known in cellular for helping with occupied bandwidth. But I think phofmanās solution using a low-pass filter to help isolate the individual contributions from the DAC and ADC is extremely novel.
Would it be possible to display the distortion residual as an option in the TIME window? This would be nice when testing power amplifiers to show things like crossover distortion artifacts.
That was my original request. Matt said they would add it to the Visualizes when they can. It will be nice to be able to look at the phase of the residual compared to the fundamental.
āIt would be niceā if there were a way to enter a different value both Left and Right loads (as well as a left and right external gain under the dBr settings)ā¦
Hi Matt,
Just checking on the residual visualizer and also when an official stable version of the 1.x software will be ready.
Thanks
Hi @Botte, I think the next release (1.133) this week will have the residual visualizers. What bugs in 1.132 are blocking and Iāll try to make sure they are fixed for 1.133.
Hi Matt,
I donāt see the residual visualizer. I see the wow and flutter v1.0
Is it not under the visualizer drop down?
Thanks,
Hi @Botte, OK, fixed, itās should be there now.
Hi Matt,
It works Great!
Thanks
Rev 1.135 does not remember the last folder that you loaded your settings from or USER Weighting File from- it always defaults to the 40x folderā¦
Hi @Var, I donāt think it has ever remembered. it always defaults to the UserWeighting and UserMask directories. Thereās a work item to change it, and I see a note in the code. But itās not been done yet.
In the previous revision it remembered the last folder that I selected to pull the user weighting from. Mine are all in the QA402 UserWeighting folder and I have to reselect it each time now. Same thing with the Load User Settings (I incorrectly said user mask before). It will always go to the QA40x folder, even after I selected from the QA402 folder. For both instances, I have not closed the program and restarted it. I have not tried the Save bitmap feature yet to see if it remembers the last folder you saved to last- that was a āproblemā you fixed beforeā¦ Thanks as always! I made a short video of what I am describing, I guess I could just keep everything in the QA40x folderā¦
soory wrong thread - canceled