Интегральные усилители — Line Magnetic LM-300IA PLUS

The LM-300IA PLUS is a single-ended triode two-channel amplifier with its own volume control, made by the Chinese tube electronics company Line Magnetic Audio, and it relies on the 300B as its output tube. Each channel runs in pure Class A, and each chassis is handcrafted, with the circuit joined by point-to-point wiring and hand soldering. A removable metal cage protects the tubes, and the case is finished in piano lacquer. The company built its name repairing and restoring classic Western Electric equipment and producing reproductions of Western Electric electronics, horns and speakers.

Key specs that matter

Rated output is 10 W RMS per channel. The published frequency range runs from 10 Hz to 50 kHz. Speaker terminals offer 4, 8 and 16 ohm taps. The unit is 435 mm wide, 217 mm high and 365 mm deep, and it weighs 34 kg. Around the back sit three RCA line input pairs, a power amplifier input for an external preamplifier, an RCA subwoofer output and a 6.35 mm headphone socket. Volume is set through an ALPS potentiometer, and an infrared remote adjusts the level. The RCA sockets on the rear panel were developed specially for this amplifier.

Engineering and use context

Signal passes through three tube stages. The input stage uses an Electro Harmonix ECC81 (12AT7) together with two 6SL7GT tubes from Tung-Sol, two LINLAI 274B tubes act as drivers, and two PSVANE 300B triodes form the output stage, one per channel. Power comes from custom toroidal transformers, while a pair of wide-band EI-core output transformers couple the 300B tubes to the speaker terminals. Bias is adjusted from the top panel, where a real ammeter shows the idle current so that it can be checked and corrected as the output tubes age. A soft-start circuit and a 30-second delay protect the tubes at switch-on. The power amplifier input lets the LM-300IA PLUS work as a stereo power amplifier under a separate preamplifier, bypassing its own volume control. In North America the amplifier has sold for just under USD 4,000.

Pairing

The subwoofer output gives a path to an active subwoofer for the lowest octaves, and the choice of 4, 8 or 16 ohm taps lets the amplifier match loudspeakers of different nominal impedance, including Line Magnetic horn systems such as the LM-3.

Alternatives

The Line Magnetic LM-212 Premium is a larger single-ended integrated amplifier that uses 212 output triodes to deliver 50 W per channel.