I’m new to this software, please be kind. When I try to change the load resistance from 10 ohms to 8 ohms in the strings menu, it keeps changing back to 10 ohms at start up every time. Is there a way to save this setting?
Yes, when the program starts up it reads settings from the configuration file named QADefault.cfg saved in the Documents folder - if the file exists. So, after you make the impedance change click the Save button in the top right and save the configuration into QADefault and on the next startup it will have your saved changes.
Mark
Also, instead in the Settings tab you can click on the ‘Save on Exit’ option so your session settings are autosaved when the app closes.
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Just a note that 1.1.31 released today. This version adds support for testing DACs and other 3rd party Windows-compatible audio output devices. The changes are fairly extensive so like any release there are risks.
The usual included Help file has a link to a page about the external device support. This tested well with USB DACs though not so great for Bluetooth DACs which have high latency and variability.
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So far it is working flawlessly with a USB DAC. This is amazing. I am still playing with it and will let you know any issues so far none whatsoever. Thanks a whole lot for this, Mark
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Is phase measurement possible with the current version or possible to add? i.e. 20-20k phase L vs. R.
Similar to QA40x automated test’s AmpFrequencyResponseChirp plot phase and use right as reference.
Yes, in the second last tab (which says either Response, Gain, Impedance, or Crosstalk since it has four sub-tests in it), all the tests are phase-accurate. The Response test shows two channels of data and the phase is relative (not absolute). The Gain test is probably what you’re looking for. It compares the input(left) channel with the input/source (right) channel and produces a gain/phase curve (a bode plot).
Mark
Also note that all of those four tests allow either a chirp source or a swept sine wave since the chirp is way faster and has more data points but may be less accurate.
Note 2: the online help (the help button) at the end discusses the required connections for each of those tests.
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Thank you Mark for adding the USB output!
Not sure if it’s by design, but in the Spectrum window when I change the attenuator the noise level is not updated, and I need to stop and restart. (I find the autorange a bit unreliable). Is there a setting for that somewhere? I don’t need to do that in the original QA app, it just updates.
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Hi, yeah it is by design. It acts like the gain calculation used for autorange and only happens once - when you click start - because it’s an entire analysis (with no signal).
The QA app and I have slightly different use cases, sorry, but since you get most accurate noise floor result with no signal and for most stereo equipment testing the noise doesn’t change I do it that way.
I know it’s long and rather tedious but the Video tutorial covers these issues in gory detail. It does have a table of contents you can click through, which helps. The section on Auto-ranging the attenuator at 8:42 is pretty good and not that long - it might be worth watching.
Mark
By the way, if you’re tweaking components to minimize the noise and just want to watch it… the data summary box on the second row shows the total signal amplitude so you can watch that value with no signal as you tweak the components.
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Thank you again Mark for this software. I would love to donate in some way. Do you have Patreon or a Paypal account?
Hi,
I don’t have a way to pay - no Patreon or Paypal account - but I appreciate the thank you. My time expenditure on the product is bursty - I work on it when I feel like it - and as long as I’m not paid I’m free to not-implement features I don’t care about. I do pay attention to the forum and try to implement stuff people want but I don’t feel obligated.
I am now working on a project for Matt/QA (thanks to QA40xPlot’s popularity), so this has led to some compensation.
Thanks
Mark
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So next Quantasylum Software is MARK² featured, nice 
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Hi,
Tool feels pretty solid, but is it possible to add I2S as source?
Most of my DUT’s are I2S input and I normally use the front connector of the QA403.
This plot tool does not support that as source and as such it does not give any signal.
Thanks.
Jan-Paul.
Hi,
I’ve never used the expansion connector but a read of the Wiki seems to indicate that it just echoes the internal DAC. So, I’m not sure there’s anything I need to do to support the I2S. Is it not generating anything when you generate a signal with the App? Try using the REST interface (see the Settings tab) and see if that generates a signal, which would give me a clue as to how to proceed.
Mark
Hi Mark,
Super thanks for your reply.
Basically I use myself Python scripting with rest myself. There are rest commands to set I2S on.
Then also some settings are needed.
Below you can see a pyhon way on how I do it with Rest:
Please let me know if this helps.
FYI:
In my python style programming I also control lab equipment over serial or with pyvisa.
Then I also loop f.e THD=f(Pout) graphs with different supply voltage levels.
Another graph which I run quite often is to measure Pout_1%_THD=f(Vbat) at several frequencies.
Thanks. This absolutely helps.
This is not a long term solution… but you might be able to run QA40xPlot in REST mode and then enable the I2S generation with a tiny python script as you show above. Just the three I2sGen settings calls. A quick look at the REST part of QA40xPlot seems to show that I’m not calling the SetDefault method so you should be able to enable the I2s anytime.
To use REST, turn on REST interface in the Settings tab and then save the settings into QADefault.cfg in Documents. Alternately, as long as REST is turned on before you start any tests it should work also for the single session. fwiw I never use REST and haven’t tested it in a while but I”m pretty sure a couple of users exercise it.
Mark
I forgot to mention that QA40xPlot in REST mode requires the QA40x app to be running - since that is who it sends REST calls to.
Hi,
since the last update again the software it doesn’t remember the windows posoition. Did you change anything?
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@cfortner Whoa, thanks for the nudge.
I did something I thought was totally benign (rename a class to more accurately describe it) and despite checking I missed a reference. Not great. That causes it to not-load window size. I’ll take care of it for the next release since the fix was two characters in one line. Sorry.
If you want to hack your config file (which is a text file) to fix the loading just change “Main” to “MainVm” in the one place it occurs.
Mark
No problem, it doesn’t hurt!
Thanks for your excellent work!
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Did a search here and looked in the help file, but is there a way to select dBr units in the Response tab? I can in other tabs.
Sorry that tab is pretty restrictive and doesn’t support any unit changes. Things like impedance wouldn’t make sense for most units and gain and crosstalk are both unit-specific. I’m not sure what the reference would be for dBr in Response. What are you looking to have it do?
Mark
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