Усилители мощности стерео — Luxman M-900u

The Luxman M-900u is a stereo power amplifier built around ODNF 4.0, Luxman's distortion-only negative feedback circuit, with the aim of ultra-low distortion. Its US list price was USD 19,900, and its matching preamplifier is the C-900u. It can also run as a bridged mono amplifier, and a front panel LED indicates when BTL mode is active. The 48 kg chassis measures 440 x 224 x 485 mm, has an aluminium front panel and stands on graded cast-iron feet meant to damp vibration. Operation stays in class A up to 12 W per channel.

Key specs that matter

Rated output is 150 W per channel into 8 ohm and 300 W per channel into 4 ohm, with an instantaneous maximum of 1,200 W per channel into 1 ohm. In mono mode, the amplifier delivers 600 W into 8 ohm and up to 2,400 W into 2 ohm. Input sensitivity is 1.24 V for 150 W into 8 ohm at a gain of 29 dB. Input impedance is 51k ohm unbalanced and 34k ohm balanced. Frequency response is flat within 0.1 dB from 20 Hz to 20 kHz. Class AB operation covers the range above the class A region up to the 150 W rating. Total harmonic distortion is 0.008% or less at 1 kHz into 8 ohm and 0.1% or less across 20 Hz to 20 kHz. Signal-to-noise ratio (IHF-A) is 117 dB and the damping factor is 710.

Engineering and use context

The output circuit of each channel pairs three-stage Darlington drivers with four push-pull pairs in parallel, in a 4x2 layout. The power supply is based on an EI type super-regulation transformer rated at 1,250 VA and a block of four 20,000 uF capacitors, and oxygen-free copper busbars carry current to the output stages. The layout is designed without ground loops. A large needle-type analog meter with LED illumination shows output level. Power consumption is 540 W in operation, 280 W with no signal and 1 W in standby.

Pairing

Two XLR inputs with a phase inversion switch and two RCA inputs are fitted, so either type of preamplifier output can drive it. Two pairs of heavy screw speaker terminals, a system bus socket and a ground terminal are on the rear panel. The output figure into 1 ohm indicates that it is specified to keep delivering current into very low impedance loudspeakers. For higher output, two units can be bridged so that each drives one speaker in mono.

Alternatives

The Luxman M-10X is a stereo power amplifier with LIFES Version 1.0 feedback, a new feedback design and a damping factor of 600.