Предусилители — Line Magnetic AS-129B

The AS-129B is a valve line preamplifier built in Zhuhai, China, by Line Magnetic Audio, whose current catalogue lists the design as the LM-129 in its Retro Preamplifiers group, next to the LM-44, the LM-1126+20B Dynamic Expanding Preamplifier and the V-02 transformer volume controller. Its circuit goes back to the Western Electric 25B, a console originally built for radio stations and broadcasters. Line Magnetic took the 130A, 129A and 18A sections of that console, merged and reorganised them, and added the parts needed to turn a studio unit into a preamplifier for home use.

Key specs that matter

Amplification is handled by four 6J7 valves, and a single 274 rectifier valve, also listed as the 5U4, handles rectification in the power supply. Line Magnetic rates the frequency response at 10 Hz to 20 kHz and the gain at 9.6 dB. Input impedance is given as 100 kohm or 600 ohm. The chassis measures 500 mm wide, 250 mm high and 425 mm deep, and the unit weighs 24 kg.

Engineering and use context

Both ends of the signal path run through transformers. At the input sits a 1 to 1 replica of the Western Electric 618 transformer, and at the output a 197A type transformer feeds the outgoing line. Line Magnetic fitted a switch that lets the owner bring the input transformer into the path or take it out, and the choice between the two connections is left to the listener. Among the Western Electric designs Line Magnetic has reworked, the company singles out the 25B and the 1126 as the two finest preamplifiers the American firm produced, and both now appear in its range, the 1126 as the basis of the LM-1126+20B. The same catalogue carries a wider body of Western Electric based work, including the LM-25B Audio Playback System, the LM-124A amplifier, replica horn drivers such as the LM-555 and LM-22A, and field coil woofers.

Pairing

Within the brand, the natural partners are the Retro series mono power amplifiers, namely the LM-86A with 300B valves in push pull, the LM-91A with a single ended 300B, and the LM-212, or the Analog series AM-2 and AM-3 300B mono power amplifiers. For a complete Line Magnetic chain, the AS-121 CD player and the AS-129P phono amplifier cover the source side, and the brand's barrier and horn loudspeakers, such as the LM-7395, LM-7396 and LM-812, complete the system.

Alternatives

The Line Magnetic LM-44 is a directly heated valve preamplifier from the same Retro Preamplifiers group of the catalogue.