I am on vacation at this moment but will do a closer analysis about mid august. My handicap is that my only way of measuring the high-frequency content on the outputs is a high-quality and very fast oscilloscope. It is good only for A/B testing, but no way of providing absolute measurements. I will post my results here when available 
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Hi Christian, did you make some progress at this topic?
Hi Sven,
Unfortunately, not, I broke my right collar bone some weeks ago, and with this handicap, I have not been able to do any detailed electronics work. This is on my to-do list, but I think and hope it will be late Novemeber when I can continue. I will post here any results. For now, I would suggest using an external low-pass filter to filter out any high-frequency residuals, if they are interfering with your measurements.
Cheers, Christian
Hi Christian,
Sorry to hear this of your bone. I wish you good recovering. The noise thing is not urgent.
All the best, Sven
Hi, after buy of an old hp spectrum analyzer 8590A for my RF hobby I could now show the residual of my QA403 left and right output unbalanced connection. Since the RF input is 50 Ohm the signal is attenuated. The residual signal is between 500 and 600 MHz. Used GEN1 but in STOP position. The capability of the analyzer does not show signals with smaller level as I can measure it with my analog level meters. Update with a higher resolution spectrum scan since I learned little more to use this analyzer. Last pic here.
