Dear Matt,
We do test a lot of different amps, (we have an AP Sys 2 and an Agilent U8903A) but the largest can output ca 180Vp, 360Vpp. This specific one is a fullbridge class D amp, and the + output is equal and opposite as the - output. That means, that on either + and the - Outputs we have 180Vpp max ac voltage (90Vp).
Cheers,
Tamas
Hi @Rammis
the RMS volt measurement was added to 0.999 and the ability to specify a preference for dB or Pct was included too. Link to more details below:
I may have missed it, but it would be nice to be able to get to the āadd measurementsā screen if there are no empty āspacesā available in the top portion of the screen- you have to close one of the measurements and then you can get to the screen to add the one you just closed and then add anotherā¦
Hi @VAR, you can, just click in the gutter between the tile and the edge, and it will open the measurement dlg and you can add another measurement and a new row will start.
Thanks Matt!. BTW, does the Q402 have a web interface like the Q401 does? I was noticing how some of @Blurpyās posts have that āWEBā display and that would be nice to use sometimesā¦
@VAR I just got a QA402, so Iām working on it.
You can find it here: GitHub - blurpy/qa40xw: Unofficial web interface for QA402 Audio Analyzer
I havenāt gotten to updating screenshots or making any releases yet, but you can just download a zip of the main branch for now if you want to test it.
I downloaded it and will try it this afternoon (Tucson, AZ time). I just got my father inlawās Pioneer VSX-D603S āA/Vā receiver circa 1994 and have started testing it for fun, and will now try with your interfaceā¦Thanks Mucho!
If I am understanding correctly, I could measure nearly 200w across an 8ohm load (differentially, and both L & R channels) without going into the special test mode?
I tried using it but got an error on the web page āThere was a problem with the requestā- am using Chrome and I tried with both the QA402 software running and not runningā¦
@VAR Not sure what it could be. Which version of the QA402 software are you using? Iām on 0.997 since I need the mono version for Linux. Perhaps something has changed in newer versions of the software?
Can you open developer tools in Chrome and check for error messages in the Console tab? Press F12 to open, and you might need to reload the page to see any errors there. A screenshot and a description of what you did to get the error is very helpful.
I am using the latest version, I think it is .992. Here is the error in Chrome (I think):
Does not mean much to meā¦ thanks for helpingā¦
Ah, looks like you started QA401 Web. QA40x Web should connect to port 9402 instead of 9401.
I guess you downloaded v1.3.0 from releases on github?
I have not created any release for QA402 yet, so you need to get the development version on the main branch. You can get it by clicking the green button that says āCodeā on github, and āDownload ZIPā.
Iām able to reproduce that error if the QA402 software is already doing acquisitions. Make sure itās not doing anything, and the messages in the status bar looks like this:
Does that fix it?
Thanks. I think the QA402 software is running. Am getting ready to leave town for a few days so may not be able to try until I get back- that will suck. Will let you knowā¦OK. I could not wait that long so hooked it up to another computer that I have not used the qa402 on and it worked!!! Now I have to wait till I get back to measure something- a carver c1 preamp most likely. I know where to go if I have questions!
Excellent, glad it worked! Maybe the first computer just needs a reboot?
Yes, feel free to ask questions 
I hooked the QA402 up to my main computer- this was the 1st time I hooked up to that one since the other PC I run the QA402 is in my workroom and I was in a rush to get to the airport but wanted to know if it worked and it would have taken some time to boot up the other PC and all. It should be fine with that PC- will know in about a week for sureā¦Thanks again, that interface looks pretty sweetā¦
I think I was able to reproduce the issue without having the QA402 software doing acquisitions.
I was just changing some settings with the web interface, and then I started getting a mix of Hardware is not idle in RunSingleWebserver and The QA402 hardware is not connected when trying to acquire from the web interface.
The status bar looked like this at that point, while being idle:
The QA402 software did not respond at this point, so I had to kill it. After starting it again the status bar looked like this:
The QA402 software responded to buttons, but nothing would show on screen.
I quit, unplugged the power to the QA402, and restarted the QA402 software, and it started working again.
@matt maybe there are some race conditions in the api from the web interface sending lots of post requests? I remember we had some of those in QA401H.
Thank you 
Yeah, I guess you ended up in the same inconsistent state that I did just now, and itās easily fixable.
Just thinking about Measuring very low distortion valuesā¦. Would it be possible to use the QA402ās 2nd generator output and an external very low THD 26dB/32dB amplifier (low THD as it has to work not to 4 Ohms, but to 1kOhm-10kOhm impedance) with variable LPF (for testing Class D amps having a large amount of Phase shift above 10kHz already) to work as a tracking notch filter? (The external amp would substract the amplified output of the 2nd Generator from the DUT output voltage and so it would send it into the QA402 Input)
It seems to easy to do so, but I might be wrongā¦
