Some more testing results:
I attached an external high quality Hi-Fi type NAD linear audio amplifier via an electrolytic capacitor (for DC blocking). On that NAD amp. the audio is no longer distorted. I have a feeling that the final amp of uBitx V4 has a flaw in it.....
As far as I know, is the most common way of biasing a push pull amplifier to avoid crossover distortion:
To me it looks like there is a problem in the final amp ...
