Luxman L-550AXII Class A Integrated Amplifier
New LECUA*1000 Volume Control circuit
We say: volume controls design impacts sound quality. As the volume is changed, the power amplifiers section "sees" a changing impedance and sound quality is affected. Volume controls also degrade over time. Luxman provides a reliable alternative here:
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 preamplifier 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.
*LECUA is an abbreviation of Luxman Electric Controlled Ultimate Attenuator.
Design Details - to achieve a high-speed primary slew rate, an ultra-wide bandwidth, and a low level of distortion
We say: In order to avoid distortion, amplifiers commonly use global negative feedback - that is a way of feeding the error signal (distortion) back to the input and subtracting the error. This works, but not with short bursts of sound, that is too short-lived for feedback to work. These short bursts of sound are transients or attack - and music is full of them. Every time a guitar string is plucked, or a drum is hit, amplifiers using negative feedback would distort the transient. Luxman overcomes this shortcoming as follows:
Innovative amplification feedback circuit
The ODNF (Only Distortion Negative Feedback) LUXMAN original amplification feedback circuit, features a fast primary slew rate and an ultra-wide bandwidth 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.
Class A amplification
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.
Large-capacity power supply circuit
A high-inertia power supply circuit that combines a large capacity EI core type power transformer (to which a vibration control feature has been newly added) and a large capacitor block (10,000uF x4) is an integral part of the L-550AXII. This large capacity power supply circuit supports the sound dynamics of the unit by enhancing stability at the core of the design.
Discrete buffer circuit
A discrete buffer circuit that is the equivalent to those used in the top end LUXMAN C-900u separate amplifier is mounted on the output stage of the pre-amplifier circuit. This protects the purity of the audio signals whilst simultaneously enhancing the drive force for the power amplifier.
Low impedance transmission
The large capacity, low resistance speaker relays are connected in parallel in order to transmit the powerful drive force that is generated by the high inertia power supply circuit and the large scale output circuit without loss. Connecting directly to the speaker terminals in this way significantly improves the damping factor from 160 to 200.
The L-550AXII is designed using proprietary technology and customised parts to optimise the sound quality of this integrated amplifier. For example, the round pattern board enabling smooth signal transmission, and a Beeline construction configuring the optimal parts locations and the shortest signal routes. In addition to this, the loopless chassis structure minimizes the ground impedance increase.
Customised parts making sound quality the priority
Original LUXMAN OFC wires are used in the internal wiring of the L-550AXII achieving a smooth signal transmission due to the spiral wrap shielding on each core and the non-plating process on the core wire. The L-550AXII is designed introducing many custom-built parts and sophisticated technologies including newly developed high sound quality, low height block capacitors.
The L-550AXII is equipped with a fully-fledged phono amplifier that is compatible with MM/MC cartridges. The front panel features multiple functions such as bass/treble tone control, LR balance adjustment, a pre/power separation switch. A loudness function interlocking with the sound volume is operable by the remote control.
Improved operability and functionality
The front panel features a newly designed, highly visible meter panel that expresses the identity of the MK II model with a ‘pointer type’, LED lit analog meter. The tactile machined aluminium control knobs enable greater accuracy of selection.
|Rated output||20W + 20W (8Ω), 40W + 40W (4Ω)|
|Input sensitivity / input impedance||PHONO (MM): 2.5mV/47kΩ
PHONO (MC): 0.3mV/100Ω
|Output voltage||RECOUT: 180mV, PRE OUT: 1V|
|Frequency response||PHONO: 20Hz to 20kHz (±0.5dB)
LINE: 20Hz to 100kHz (+0, -3.0dB)
|Total harmonic distortion||0.007% or less (8Ω, 1kHz)
0.02% or less (8Ω, 20Hz to 20kHz)
|S/N ratio (IHF-A)||PHONO (MM): 91dB or more,
PHONO (MC): 75dB or more
LINE: 105dB or more
|Volume adjustment||New LECUA1000|
|Amplification circuit||ODNF 4.0|
|Output configuration||Bipolar parallel push-pull|
|Max. amount of tone control||BASS: ±8dB at 100Hz
TREBLE: ±8dB at 10kHz
|Power supply||230V~(50Hz) / 115V~(60Hz)|
170W (under no signal), 0.5W (at standby)
|External dimensions||440(W) x 178(H) x 454(D) mm
front side knob of 20mm and rear side terminal
of 27mm included in depth
|Net weight||24.3kg (main unit)|
|Accessories||Remote control (RA-17A)
|Speaker terminal Supported Y-lug terminal dimension||Width of part a: 15mm or less
Width of part b: 8mm or more
* Connection may not be performed
depending on the shape of the