Усилители для наушников — Luxman P-750u

The P-750u is a headphone amplifier from Japanese maker Luxman and a refined successor to the P-700u. Built in a full-width, low-profile chassis that matches Luxman's hi-fi components rather than a compact desktop box, it combines the company's LECUA electronic volume control and the fourth version of its ODNF feedback circuit with a fully balanced four-channel output stage. Its main external change from the P-700u is a 4-pin XLR balanced headphone socket, and it was later followed by the P-750u MARK II.

Key specs that matter

In unbalanced mode, the P-750u delivers 4W per channel into 8 ohms, 2W into 16 ohms, 1W into 32 ohms and 53mW into 600 ohms. In balanced mode, it delivers 8W into 16 ohms, 4W into 32 ohms and 213mW into 600 ohms. Frequency response is 20Hz to 20kHz within 0.1dB and 10Hz to 170kHz at -3dB. THD is 0.003% unbalanced and 0.002% balanced, and signal-to-noise ratio is 113dB unbalanced and 116dB balanced (IHF-A). There is one unbalanced input and two balanced inputs, with input sensitivity and impedance of 1V/15 kilohms unbalanced and 2V/40 kilohms balanced. Outputs are a 6.3mm jack, a 4-pin XLR, a pair of 3-pin XLRs and a line through output. Power consumption is 42W. The chassis measures 440 x 92 x 400mm, weighs 13.3kg and draws 27W with no signal.

Engineering and use context

ODNF (Only Distortion Negative Feedback) is Luxman's own feedback system, which feeds back only the distortion components of the output instead of the whole signal, aiming for high slew rate, wide bandwidth and low distortion. Version 4.0 uses a triple-paralleled input error-detection stage and a Darlington output stage, lowering output impedance and raising the signal-to-noise ratio. For balanced headphones, the four channels are used in pairs in bridge-tied-load (BTL) configuration, doubling voltage swing and improving left-right separation; for unbalanced headphones, the four channels are paralleled into left and right, doubling output current. Volume is controlled by LECUA (Luxman Electronically Controlled Ultimate Attenuator), a computer-controlled resistor-switching attenuator that keeps left and right channels precisely matched even at the very low settings where headphone listening often takes place, a weakness of conventional analogue potentiometers. The power supply for the pre-driver stage was reinforced over the P-700u, and the unit stands on density-gradient cast-iron feet taken from Luxman's 900-series amplifiers to reduce vibration.

Pairing

Its reserve of voltage and current lets the P-750u drive inefficient planar designs as well as high-impedance dynamic headphones.

Alternatives

Luxman's own P-1u is an earlier, lighter headphone amplifier from the same maker.