Прочие устройства — Line Magnetic AS-123

The AS-123 is a valve buffer and gain-matching unit sold under Analog Sound, the AS-series sub-brand drawn up by the Line Magnetic Western Electric replica design studio in Foshan. That studio grew out of the Foshan operation of Line Magnetic, the firm set up by the Zheng brothers, and Analog Sound runs as a separate partnership rather than as a brand owned by the Line Magnetic company. The unit does not drive loudspeakers. It sits between a source and a preamplifier, or between a preamplifier and one or more power amplifiers, and changes signal level and impedance. The price is USD 2,346.

Key specs that matter

The buffer covers 10 Hz to 45 kHz. Input impedance is 470 kohm and output impedance is 600 ohm, with an input sensitivity of 2 V. Gain is set with a 20-step control. The tube line-up is two 6K7 pentodes and two 6SN7 double triodes, with a 5U4 or 274B rectifier. Connections are RCA inputs plus two RCA output pairs and an XLR balanced pair. The case measures 480 x 200 x 200 mm and weighs 10 kg, and a version wired for 240 V mains is available.

Engineering and use context

At the output sits a replica of the Western Electric 197A transformer, and that transformer is what turns an unbalanced input into a true balanced output on the XLR pair, without a second active phase-splitter stage. Wiring inside is hand-made and point to point. Converting a high-impedance input into a low-impedance output lets the unit deliver more current into long cables or into several amplifier inputs at once. A switch flips absolute phase between 0 and 180 degrees, aimed at early recordings made before recording standards came into effect in the 1960s. Handles on both sides and a metal mesh window over the valves complete the chassis, along with a power indicator.

Pairing

Placed after a preamplifier, the output can feed several power amplifiers in parallel, so it suits bi-amped and multi-amped horn systems or a setup that adds a subwoofer amplifier. The XLR output lets a single-ended preamplifier drive a power amplifier that has only balanced inputs. Before a phono stage, CD player or DAC it can trim level so that different sources arrive at the preamplifier at similar gain.

Alternatives

Line Magnetic lists no other valve buffer in its range, so the brand offers no direct alternative to the AS-123.