I’m currently waiting on my QA403 to arrive and am wondering if it’s possible to output custom waveforms, similar to an arb generator?
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Hi @MotoDan. The QA40X software allows sine waves, multitones, and white noise, as well as expo chirp useful for evaluating frequency responses.
The QA403 REST calls support a wave binary array so in theory you can send anything. I don’t know if there’s a size limit.
The factory QA40x app doesn’t have a user-defined option nor does my software QA40xPlot but it would be pretty simple to add.
What are you trying to achieve?
Mark
Hi Mark,
I was hoping to use the QA403 (which I haven’t purchased yet) as a precision audio spectrum analyzer which it will of course do now. I also would like to take advantage of the precision of the DACs to generate arbitrary waveforms. So from what you’re saying, it sounds like I could generate a wave array offline and load the 403. I’m not familiar with the REST reference or how to program the 403.
Thanks
Yes, when you run the factory application it supports a REST interface. This is a way to send commands to the application that it then runs. REST just means that the interface is memory-less, which is necessary for multiple callers to not interfere with each other.
When you run the factory application it has a useful help entry for the REST api - that is directions on how to call the app externally. These can be done from any browser or, more often, a short program in Python or a batch file.
As a simple test you can use windows CMD (command line) and a program named curl that now comes with windows 11. Like this→
curl http://localhost:9402/Status/Version
will print the current version of the application. Or
curl -d "" -X PUT http://localhost:9402/Settings/Input/Max/6
will set the input attenuation to 6.
Take a look at:
QA40x API - QuantAsylum/QA40x GitHub Wiki
Mark
I need a GOOD square wave.
Define good. Band-limited? High bandwidth?
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Nice straight edges with little overshoot and minimal harmonics, you know… the fantasy kind.
You can have little overshoot, or you can have minimal harmonics, but not both - limiting the harmonics forces Gibb’s phenomenon to appear in full. In general for audio band-limited makes sense.
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Hi @amp-haus, I think the challenge is that modern amps like the LM3886 are showing 10V/us, which suggests a large-signal bandwidth of several MHz. And IC opamps likes the OPA1612 are around 27V/us, suggesting a large-signal bandwidth of 4-8 MHz.
And so, you are well into needing a scope to see a “true” squarewave. The bandlimiting filters in the ADC/DAC used in the QA403 are an order of magnitude below what the LM3886 and OPA1612 can achieve. If you try to look at a squarewave from an amp using the QA403 ADC, you’ll simply measure the slew rate of the ADC’s filter.
A good scope with a built-in siggen is the right tool for the job here.
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