After a pair of weeks of listenig, I tell you my impressions about the LC.
The most surprising things about this amp are the differences I can hear between my 3 favourite headphones, which I know very well:
Great matching! This headphone is very warm and bass oriented, but the coupling with LC generate a perfect balance between all range of sound.
Trebles are really precise, voices are great, the low range gets less bloomy, producing a warm and pleasant sound.
Not so good as D5000 . The middle-high range, strongest point of this headphone, becomes tinny and unless extended as canned. Low range, weak point of the AKG sound, becomes worse, and the headstage (another great AKG characteristic) gets smaller.
Sony MDR 7509 HD -
Unrecognizable! The high range is analytic but becomes much cold , middle range is backward, and the low range is too much emphasized but totally out of control!
Normally they are really precise, the opposite of what I heard with LC, I don't like it.
This is everything about headphones, let's talk about opamps!
By changing opamps, you can surely hear sound differences, but they are not so incisive and the don't change too much what I
said about headphones.
NE5532 famous opamp, it gives out an equilibrate sound, but it's a pretty normal component, not magic as I heard.
OPA6104 better than NE5532, linear and accurate on the high range.
OPA2604 and LME47920 *
they are pretty similar and very pleasant, they also mix very well the low and the high range giving a warm sound.
*without the box, this opamp has a little problem, I heard some treble distortion, which disappeared by closing the box.
OPA627 accurate, balanced, perhaps tending warm, detailed, it's not always the best choice because sometimes it seems to be "away" without personality
OPA2111AM the most detailed in the middle-high range, maybe a bit cold ant too much bright.
CLASS A MOD
I cannot hear any difference, and I think it turns nothing in class A.
It has been a long time since I ended my studies, but I can't figure out how a resistor linked between ground
and output could change the class of the opamp. ( 1, 4 pins are output - 7 pin is GND )
Synthetically: I know I wrote a critic review, but it's what I heard, LC is well built, not magic and it's a pay for value. But attention to the coupling with various headphones.
I'll modify LC following the suggestions I received in this forum
Thank you, BlaBlaBla and francisdemarte, Flukell and other