Интегральные усилители — Line Magnetic AS-125

The AS-125 is a single-ended integrated amplifier from Analog Sound, a line produced by Line Magnetic Audio of Zhuhai, China, and built around a pair of 211 transmitting triodes. Line Magnetic describes the circuit as a straight hot 211 design in Class A, and credits the late Zheng Cai, who studied classic Western Electric designs, with work that brought the 211 into its modern amplifiers. A monoblock sibling, the AS-125PP, is sold as a pair. The AS-125 is priced from AUD 13,200.

Key specs that matter

Output is 18 W RMS per channel from one 211 per side, with three 12AX7 valves at the input and two 6SN7 double triodes as drivers. Four pairs of RCA inputs are provided, and the speaker terminals offer 4, 8 and 16 ohm taps. Gain is switchable between 40 and 52 dB, input sensitivity is 500 mV and input impedance is 100 kohm or 600 ohm. Frequency response runs from 10 Hz to 45 kHz within 2 dB, the signal-to-noise figure is 88 dB and distortion is 1 percent. The case measures 480 mm wide, 275 mm high and 490 mm deep, and the net weight is 50 kg, about 70 kg crated.

Engineering and use context

The 211 is a large directly heated triode first made for radio transmitters, and it needs a much higher plate voltage than small audio valves, so the amplifier needs its own supply for that stage. Line Magnetic uses two power transformers, one for the high voltage stage and one for the low voltage stage, each with its own mains inlet on the rear. The output valves are auto biased, so no adjustment is needed when they are replaced. Rather than a simple volume control ahead of the output stage, the AS-125 has a proper preamplifier stage, and its input passes through a replica of the Western Electric 618 input transformer. A front panel switch sets the unit as an integrated amplifier or as a power amplifier driven by an external preamplifier, and a front meter can be switched off. Assembly uses hand-soldered point-to-point connections throughout. Options include 12AX7EH, ECC83, ECC803 and 5751 as options for the input valves, and 6H8C, 6F8G, CV181 or ECC32 for the driver position. The finish is grey.

Pairing

With its modest single-ended output, the amplifier suits efficient speakers such as horns, large full-range drivers or two-way designs with a benign load, and the three output taps allow the transformer secondary to follow the nominal impedance of the speaker.

Alternatives

The Line Magnetic LM-88IA is a push-pull integrated amplifier with four KT88 valves giving 42 W per channel in fixed bias or 30 W in cathode bias.