That is pretty interesting.. I have built plenty of different SE and PP amps over the years...One thing that makes a huge difference on how the amplifiers presentation..Is the rectifier tube.If you have a rectifier that has a larger volume drop,Music like jazz,country or blues sounds smoother and more relaxed.But, Changing the rectifier to something with less voltage drop.Works better for classical,rock, pop or more detailed or complicated music... On the negative feed back..A majority of amps use to much,That will suck the life and details out of the music..