Sneak Peek: The QA402

QA40x
101

I hooked up the QA402 and did some testing.
First thing it did was a firmware update. It then needed a power cycle to come back on line.
I found that the software is pretty intuitive, although I did manage to bomb it a few times.

I was wondering about the THD % tile, can you increase the decimal places to say 5?

Looking forward to running some of the plug-ins for power and distortion.

Thanks

102

Hi @Botte, glad the unit arrived. There should be a SW release today or tomorrow that pulls in the frequency response measurements along with other bug fixes. Noted on the tiles with % and precision. Thereā€™s a crash issue with zooming in the graph and markers that will be merged in early next week. Is there a specific plug-in from the QA401 youā€™d put to use? If so, I can get it into the release for next week. Thanks for your patience.

103

Thanks Matt,
PWR THD vs output power; would be great to have.

104

QA402 can work like a DAC ? Can we listen music with it ?

105

Hi Matt, not sure if you were aware but the PDF for the QA402 says QA401 at the top:

106

I have been doing some more testing.
I see that the context menus donā€™t always popup on right click, they do if you hold the left button down.
Iā€™m also wondering about some increased precision on the output level. With one dB steps I seem to be under or over my one watt level Iā€™m shooting for.

Thanks,

107

Oops, I see that I can change the level with the context menu for the generator.

108

PWR THD vs output power

Noted, should be in next release

QA402 can work like a DAC ? Can we listen music with it ?

Not currently

but the PDF for the QA402 says QA401 at the top:

Fixed, thanks!

I see that the context menus donā€™t always popup on right click

Should be fixed in next release

I see that I can change the level with the context menu for the generator.

There is a bug that will be fixed for next release: In the Gen context menu you can set the sensitivity ty of the amp up/down button. That was being ignored (always 1). But in the next release it is respected. Also, note if you set the sensitivity to 1 dB, if you control+click the amplitude button then it will move 10X more (10 dB per click). And if you alt+click the amplitude button, it will move 0.1X more (0.1 dB/step)

There is also a bug where input left/right are sometimes swapped that is being worked on. The fix might not be in todayā€™s release, but hopefully this week.

Front-panel I2S has been confirmed on the previously mentioned isolator board at 32 bits at 48K. But thereā€™s a issue where the front-panel output DAC data hangs that is being studied. So the I2S button is disabled for now. The control cluster has the re-organized in the next release too to hopefully better convey intent

image

Thereā€™s also some more visual changes to better convey whether you are in ā€œtonesā€ mode (fixed sines) or chirp mode (in freq response mode).

The FR setting gets its own amplitude control button too as previously you had to go into the context menu to change.

image

109

Release 0.990 is up here

110

Hi Matt,

How do you make the graph of THD vs power logarithmic for power?

Also, I like the new fixes.

Thanks

111

Hi Matt,

I have a question about the attenuators, when I turn it off I see a much lower 60 and 120 Hz power spikes. They move up and down with the noise floor with the atten. Does this make this a test setup noise issue?

Thanks

112

Well, I keep answering my own questions, maybe this will help others.

It was my laptop power supply. When I went on batteryā€™s the noise floor issue resolved and worked as expected.

Thanks

113

Noted, will be fixed.

114

There are two things to keep in mind here. First, is that the system will generally deliver a constant dynamic range. That is, when the max input moves from 0 dBV to 6 dBV, the measured noise (RMS, 20 to 20 kHz) will increase by 6 dB. So, your noise is 6 dB higher, but your max input is also 6 dB higher.

The second thing at work here is the associated resistances. At 0 dBV max input with inputs shorted, the equivalent input resistance is about 500 ohms. At 18 dBV max input, the eq input resistance is about 6k. That 6k has considerably higher thermal noise, and the bias current of the opamp (OPA1656) is also suffering a bit there too BUT, as the OPA1656 is CMOS, the bias current noise is very small relative to the thermal noise.

In short, just think of the analyzer as delivering a constant dynamic range and that will let you estimate the noise floor at every input setting. If the RMS noise is -115 dBV (0 dB input), then at 42 dBV input, we might expect the noise to be at -73 dBV

115

Hi just wondering when the QA402 will be available for purchase for international shipping?

116

Hi Damian,
I received my QA402 last Monday (31st of May, ordered on 10th). Iā€™m living in Frankfurt, Germany.
Regards, Norbert

117

Sounds good, thank you Norbert.

118

Feel free to start another thread on QA402 questions and issues as this thread is a bit long and Discourse isnā€™t great on super long threads (but itā€™s excellent on short threads).