[rockbottom]

I'm quite interested in knowing the differences in the 2 operating modes.

I do hear an audible difference but I was wondering if anyone can provide some technical view points.

 

[Balisarda]

I think I know a little part of this. Vacuum tubes by themselves have a very high output impedance. That would be bad for driving speakers or any kind, because the impedance mismatch would cause a lot of stacking and treble roll-off. Using a transformer is one way of stepping down the impedance to something useful for driving headphones and loudspeakers.

But some people think transformers color the sound of the signal or make the amp more sluggish in reponding to signal changes. So they seek ways to step down the output impedance of the amp without using a transformer.

I don't know anything about how they actually do this, but Woo Audio and Berning both offer OTL amplifiers. I think Berning's website actually explains somewhat the technology he uses, but I can't recall having understood it.