I just learned that the AKG K340 cannot be driven by aa tube headphone amplifier...
It is not just a question about raw power in watts because of his 91 Db sensitivity......
It is not just about his high impedence 400 ohms...
It is about the fact that two cells of 400 ohms each seems to ask a dedicated power amplification..
I am not knowleageable in electricity coupling factors...
But the K340 was designed at the times where there was no headphone dedicated amplifier with so much low impedance headphones in the market as today...
The K340 was designed with the idea that the headphonbe out of a regular power amplifier will do it...
The headphone amplifier with which i test it was a very good and known one, but the difference between the headphone out of my Sansui alpha was staggering...
The K340 is unique in his features and design... There is no other headphone like it...
If you drive it with an headphone amplifier and think because it is able to put it at listenable level that it sound good and optimal, then you have never listened to the K340 really...
It is my conclusion because the difference was so astounding on all acoustic count, that it was not the same headphone at all driven by an headphone amplifier even a powerful good one and the headphone out of my Sansui alpha... The most apparent lost when driven by an headphone amplification, even a tube one, was the lost of my holographical imaging and the lost of my "out of the head" soundstage even if all details of the soundfield was there ... And the mids frequencies body were thin and recessed...
If you have a K340 test it with a power amplifier... Keep the headphone amplifier for the other headphones...
Anyway well amplified i will never go to any other headphones at any price ... As i said already....
The ONLY and sole upgrading now will be the BACCH filters of Dr. Choueiri...
Anyway i am happy as i am now with no more illusion about upgrading anything especially amplification...
The Sansui alpha is a gem and not an obsolete technology from 35 years ago, i am now sure about this fact...
My best to all ...