Усилители мощности стерео — Luxman M-700u

The M-700u is a stereo power amplifier that Luxman of Japan describes as a middle range model in its solid-state line, inheriting the drive circuitry of the bigger amplifiers. The circuit works in class AB and uses bipolar output transistors, and it can be switched to bridged mono operation when more power is needed than a single stereo chassis provides.

Key specs that matter

Rated output is 120 W per channel into 8 ohm and 210 W into 4 ohm in stereo. Instantaneous output climbs to 840 W per channel into 1 ohm. In bridged mono mode the rating becomes 420 W into 8 ohm, with an instantaneous 1,680 W into 2 ohm. Input sensitivity is 1.1 V for full rated output, gain is 29 dB, and input impedance is 51 kohm on RCA and 34 kohm on XLR. Between 20 Hz and 20 kHz the response stays within 0.1 dB, and it extends from 1 Hz to 130 kHz at the -3 dB limits. Distortion is 0.009% at 1 kHz into 8 ohm and 0.1% across the full 20 Hz to 20 kHz band. Luxman gives a signal-to-noise figure of 115 dB with IHF-A weighting and a damping factor of 350. The amplifier draws 370 W in operation, 110 W at idle and 0.4 W in standby. It measures 440 x 190 x 427 mm and weighs 27.5 kg.

Engineering and use context

Feedback is handled by ODNF 4.0, which Luxman calls the latest version of its feedback circuit and says improves distortion and noise figures over earlier versions. Each channel uses a push-pull output stage with four parallel pairs of transistors in a three-stage Darlington arrangement, a layout chosen for high current delivery into difficult loads. The power supply rests on a 550 VA EI type transformer and a bank of block capacitors totalling 80,000 uF. Internal wiring follows the shortest possible paths, a method Luxman calls beeline wiring, to keep transmission impedance low. Two illuminated VU meters on the front panel show the signal level of each channel. At the back there are RCA and XLR inputs, heavy-duty speaker binding posts, switches for stereo or mono operation and for phase inversion, and a remote input terminal for custom installations.

Pairing

The standard input sensitivity means any preamplifier with a normal line output will drive the M-700u to full power. Given its current delivery and damping factor, low-impedance or low-efficiency loudspeakers are a reasonable load, and two units in mono mode suit larger speakers that ask for more current.

Alternatives

The Luxman M-10X is the stereo power amplifier above it in the range and introduced the LIFES feedback engine in 2021.