Thermal memory distortion

[a supprimer merci]

(04-04-2019, 03:40 PM)Lawrence a écrit : ECDesign, je ne connais pas du tout. J'ai vu un site hollandais qui propose des blocs mono de 25 watts en classe AB à plus de 800 Euro. Est-ce cet objet? Bref, qu'est-ce que c'est-y que ces créations?

Voir ici: http://forum-hifi.fr/thread-5709-post-24...#pid240783

Quelques explications pour les spécialistes (qui font référence à un schéma que je n'ai pas rajouté, mais les techniciens--pas moi- devraient pouvoir suivre) :

"The MBL circuit is rather simple and straight-forward and there are only few transistors in the signal path. I use no CCS nor current mirrors in the differential stage, only pure resistive loads that maintain same impedance over a very large bandwidth. Differential stage gain is set by the coupling resistors R13 and R14 that form a triangle with resistors R23/R24 and R25/R26 hence the name double delta stage. VAS stages T7 and T8 sense the differential current output of the double delta stages. The ac voltage swing across R6, R7, R17 and R18 is minimal, this helps to minimise the Miller effect that would introduce non-linearity and bandwidth limitation with a voltage output differential stage. The open loop bandwidth of this amplifier runs into 50 MHz, so I had to apply band limiting to approx. 2MHz to keep the circuit fully stable under all conditions. This is achieved by adding C1 and C2 for band limiting.

The double delta stage helps to operate transistors T1, T2, T5 and T6 at more or less constant power as there is no shared emitter resistor / current source, this together with the relatively high thermal mass of the BD139/BD140 (integrated heat sink) offers low thermal memory distortion. "

Et sur le fameux effet thermique:

" I use medium power transistors BD139/BD140  (higher thermal mass, heat sink) for the error amplifier, together with current steering of the error amplifier this results in very low thermal memory distortion. Thermal memory distortion creates a rather grainy fatiguing sound. Tube amplifiers do not suffer from thermal memory distortion due to the high and constant cathode temperature. Therefore tubes do not sound grainy like most semiconductor amplifiers. 
Tiny transistors often used in audiophile amplifiers have very low thermal mass and the chip temperature can vary more easily with applied power. These will usually cause that typical grainy semiconductor sound. Because these tiny transistors are also used in the most critical part, the error amplifier, related thermal memory distortion cannot be corrected by global feedback and thus remains audible."

Je n'y comprends pas grand chose mais le résultat me plaît beaucoup