Усилители мощности стерео — Luxman MQ-300

The MQ-300 is a valve amplifier for two channels, which Luxman built to mark its 90th anniversary. Announced in June 2016, it takes its design cues from the MB-300 monaural amplifier of 1984 and centres on a pair of TA-300B directly heated triodes made by Takatsuki Electric Industry, which Luxman describes as the only 300B tube produced in Japan.

Key specs that matter

Rated output is 8 W per channel, available into 4, 8 or 16 ohm loads through separate speaker terminals, with the 16 ohm tap intended for vintage loudspeakers. Input sensitivity is 490 mV at 8 ohm and input impedance is 240 kohm. Luxman lists a response of 20 Hz to 20 kHz within +0.3 and -1.5 dB, total harmonic distortion of 1% at 1 kHz and 1 W into 8 ohm, while noise sits 105 dB below output, IHF-A weighted. Power draw reaches 190 W, and versions for 230 V at 50 Hz or 115 V at 60 Hz exist. The chassis measures 460 x 237 x 340 mm and weighs 29.0 kg.

Engineering and use context

Luxman chose a single-ended stage without global negative feedback. Four TungSol 6SN7GTB tubes form a two-stage driver with parallel connection, and two Sovtek 5AR4 rectifiers feed independent left and right supplies that use FINEMET core choke coils. The output stage runs cathode bias, which Luxman says reduces sensitivity to heat and mains variation, and the heaters are lit from DC to keep hum low. Each channel has a large output transformer with an oriented cut core. The output tube sockets sit on a PORON floating damping structure, and parts include Luxman oil coupling capacitors, Dale metal-clad cathode resistors and large steatite insulators. The steel chassis uses 1.6 mm panels, a 2 mm base and a 12 mm aluminium top plate, standing on cast-iron gradation legs. A piano-finish natural walnut frame surrounds the metal-coated transformer covers, and the input jacks are made of copper alloy.

Pairing

With its low output, the MQ-300 is built for sensitive loudspeakers, and the three impedance taps let the owner match each speaker to the correct transformer winding. The input section offers one direct input and one variable input, so the amplifier can be fed by a preamplifier or by a source with its own output level control. The walnut frame and exposed tube complement follow the look of the MB-300 that inspired the project, and the cast-iron legs are intended to disperse vibration rather than transmit it to the shelf below.

Alternatives

The Luxman MQ-88uC is another stereo vacuum tube power amplifier from the brand, using KT88 output tubes.