I recently finished a dual unit with the older mnats board, but only today finished tweaking. When I posted that I still had some 0.1-0.2%THD 3rd harmonic and was wondering where things went wrong. Turns out it was the transformer set up, although I don't quite see why.
Now I have Lundahl in (1:1 allows a completely stupid amount of compression) and Lundahl out (1:2 allows a stupid large amount of gain), and finally THD sits at about 0.06-0.07%. It's mostly 3rd harmonic. I managed to tweak 2nd harmonic to negligible level. This was the RMAA test suite so don't know about test tones in detail, I guess 1000hz.
Another observation. This is the first build (tube, chip, solid state) where I have ever actually *heard* different caps affecting audio. I found a dramatic difference in an unexpected place: those two 0,22uF caps! I had one unit with Panasonic SMF and another with Wima MKS2(like in the mnats picture above). Those MKS2 are transient poison! I wondered if the MKS2 unit had slightly broken transistors, but it was just those caps. Any acoustic guitar strumming immediately shows what they do.
I don't get it. These differences don't measure on RMAA (THD, noise) for example, but can be clearly heard if you know what to listen to.

Then I went through some side by side testing with the three 1uF caps. Again, Wima MKS2 was really bad, I urge anyone to try, although the difference was less dramatic as with those 0,22uF ones. Wima MKS4 (250V) on the other hand sounds great, as does Mundorf M Cap. All relatively cheap.
And the sound of this unit... How much better can solid state sound get?
