New QA401 user - need help

I purchased my QA 401 2 months ago and start using it after some work delay. But my QA 401 output chart looked very weird. I tried everything without success so I decided to need some help here.

I short the - of IN + OUTPUT

And connect IN+ to OUT+ directly with my BNC cable.

Here the output in “Time” mode. Looked ok.

But the ouput on “Frequency” mode looked nothing like the manual.

Did I got my self a defect unit of QA401 ? Or it just some wrong settings?


Hi @obscurus, it looks correct for settings you have, but the settings are wrong. Try this:

  1. File->Reset Startup Defaults

And then go through the quick start guide located here:

From the picture above you are showing the “time” domain in the top picture. In the lower pictures, you are showing the output. Note the message “Output is being displayed”. This is to give you a hint that you aren’t looking at the input. The output looks so good becuase it is: It is bit-exact, and thus there is no noise and no distortion.

Hit the Input button to see what is being captured.

Finally, just to make sure: Do not short the outputs. You only want to short the inputs if they aren’t being used. For example, if you want to measure a single ended signal on L+ INPUT, then you should short L- INPUT. You dont’ need to do anything on Right Channel inputs if you aren’t using them.

Hi matt,

I can see what I was wrong. I thought the output should show the output sinwaves. Thanks, it look perfect ly fine by now.

And thank for your notice on short outputs. So if I want to connect the OUTPUT of QA401 to my preamp ( singled-end input ). I just need to use L+ OUTPUT and leave OUTPUT L- untouch ?

@obscurus, yes, you got it! For single ended measurements, leave OUTPUT L- open, connect OUTPUT L+ to what you want to measure, short INPUT L- and apply the signal you want to measure to INPUT L+.