Hi Matt
Thanks again but the video doesn't match the behaviour I have seen and as
@Earfonia has. It s very interesting and it would be great to get to the bottom of the issue.
I tried many different sources with my 401 and they all exhibited a 20 to 30 dB rise in noise floor with min to max input signal level when measured on the 401. Ignore THD and THD + N for the moment, the addition of distortion into the mix just obscures the issue.
If you look at the Earphonia measurements
https://www.audiosciencereview.com/...2-pro-with-quantasylum-qa401.6877/post-152943
you see with input dropping from 0dBV to - 6dBV to - 12dBV sees the noise floor drop from around (32k fft) - 122dBV to - 130dB to - 138dBV respectively.
So that's an noise floor increase of about 16dB with signal increase of 12dB.
This is exactly the sort of thing I would see. We can be confident this isn't the ADI as measurements with other devices don't show it.
Have their been any circuit revisions in newer units that might account for this?