Other devices — Line Magnetic Audio AS-123

The AS-123 is an all-valve line buffer from Analog Sound, the series that Line Magnetic sells under the Analog Sound by Line Magnetic name and builds around replicas of Western Electric parts. It is not an amplifier for loudspeakers. A buffer takes a signal in at high impedance and hands it on at low impedance, which is why the maker also calls it an impedance matcher and a current intensifier. It sits in a line-level chain, adjusts gain and converts a single-ended signal into a balanced one. The export price is USD 2,346, and in Australia a 240 V version costs AUD 6,600.

Key specs that matter

Frequency response spans 10 Hz to 45 kHz. Input impedance is 470 kohm, output impedance is 600 ohm and input sensitivity is 2 V. Five valves do the work - two 6K7 pentodes from GEC or RCA, two 6SN7 double triodes from Sylvania or GEC, and a 5U4 rectifier, with a 274B listed as an option in its place. Signals enter on RCA sockets and leave on two RCA pairs plus a balanced XLR pair. The grey case is 480 mm wide, 200 mm high and 200 mm deep, with a weight of 10 kg.

Engineering and use context

The balanced output comes from a replica of the Western Electric 197A transformer rather than from an extra active phase-splitting stage, so the XLR pair carries a true balanced signal derived from an unbalanced source. Internal wiring runs point to point and is made by hand. A gain knob below the valve window runs from 0 to 20 in steps, letting the user trim level between a preamplifier and power amplifiers. A toggle in the middle of the front selects 0 or 180 degrees of absolute phase, intended for early recordings made before standard recording practice took hold. Valves and the output transformer stand exposed on the top plate so that heat escapes freely. Handles are fitted on both side panels, a metal mesh window on the left shows the glowing valves, and the power switch and indicator sit at the right.

Pairing

Three positions in a system suit the AS-123. It can follow a source such as a streamer, DAC, CD player, phono stage, tape deck or tuner ahead of a preamplifier or integrated amplifier. It can sit between a preamplifier and a power amplifier. Its output can also drive several power amplifiers at once, which suits bi-amped and multi-amped horn systems or a system that adds a subwoofer amplifier. The XLR pair lets a single-ended preamplifier reach a power amplifier that offers only balanced inputs.

Alternatives

Neither Line Magnetic nor its Analog Sound series offers a second valve buffer, and the AS-123 therefore has no counterpart elsewhere in the catalogue.