Pursuing a sound that appeals to the senses whilst creating a deep musical impression is the ultimate role of the audio amplifier. With pure class A design, the L-550AXII integrated amplifier is a refined version of the L-550AX which was itself fully restyled in 2011. The MK II model boasts improved functionality with the latest technologies equivalent to the higher grade L-590AXII such as Version 4.0 of the original amplification feedback circuit ODNF, the new LECUA1000, computerized attenuator, and a buffer circuit with discrete configuration as standard. Such features result in a model with capability of expression above its class, offering a mellow and dense sound that only pure class A amplification can create. The L-550AXII is a mid-range integrated amplifier that increases its maturity in an attractive, functional design for music to be thoroughly enjoyed.

A pre-amplifier circuit-integrated computerized attenuator, new LECUA* 1000, equivalent to that used in the higher grade L-590AXII model is mounted in the volume adjustment unit, playing a critical role in the pre amplifier section.The renovation was made to the buffer circuit input stage to allow smooth volume adjustment in 88 steps thereby minimizing the deterioration of sound quality. Additionally, a 3D layout has been introduced in the new LECUA1000 allowing the substrates to be placed in three dimensions. The attenuator circuit is connected directly to the amplification circuit to make the shortest signal routes and improve efficiency. The LECUA1000 has exceptional durability and is capable of controlling the changes in sound quality that may occur due to external vibrations or sound volume adjustment.

The ODNF, LUXMAN original amplification feedback circuit, features a fast primary slew rate and an ultra-wide bandwith achieved through the feedback of distortion components only from the output signals. The L-550AXII is equipped with the latest version of ODNF - Version 4.0 - in which the distortion characteristics at high frequencies as well as the S/N performance have been significantly improved. Version 4.0 ODNF also features a large scale power amplifier with a parallel push pull structure where 3 stage Darlington is used. Both of these features are inherited from the M-700u power amplifier and the higher grade integrated L-590AXII. A rated output of 20W +20W (8Ω) of pure class A amplification achieves a mellow, expressive sound with a heightened sense of density with high drivability to speaker systems.