Усилители мощности стерео — Line Magnetic AS-125N

The AS-125N is a 211-based integrated amplifier from Line Magnetic, with a single-ended triode output circuit, sold under its Analog Sound label and using two of those tubes in pure Class A. Although it can work as a power amplifier, it has a full preamplifier stage and input switching, so it is an integrated design rather than a separate power amp. It is offered alongside the AS-325N, an export-only variant of the same amplifier with upgraded components. Its transformer work draws on the late Zheng Cai, founder of Line Magnetic, who set out to recreate classic Western Electric transformers and circuits.

Key specs that matter

Output is 18 W per channel RMS. The valve line-up is three 12AX7, two 6SN7 and two 211. Input impedance is 100 kohm, with a 600 ohm figure also quoted, and sensitivity is 500 mV. Gain is selectable at 40 or 52 dB. Quoted noise performance is 88 dB signal to noise, with a frequency response of 10 Hz to 45 kHz within 2 dB and total harmonic distortion of 1 percent. Four pairs of RCA inputs are fitted, along with speaker binding posts for three impedances. The grey chassis measures 480 mm wide, 275 mm high and 490 mm deep and weighs 50 kg, or about 70 kg crated.

Engineering and use context

The circuit uses three amplification stages, all wired by hand point to point. The input stage uses a copy of the Western Electric 618 transformer, feeding a full preamplifier stage instead of a plain volume control, and the output transformers also follow Western Electric practice. A front-panel switch changes the unit between integrated and power amplifier modes. The high-voltage and low-voltage sections have their own power transformers with two separate mains inlets, which keeps the supplies apart. Bias for the 211 pair is set by the amplifier itself, though the maker advises fitting matched tubes. The meter on the fascia can be turned off when not wanted, and the package includes a handset for remote operation.

Pairing

Given its limited power, the AS-125N is aimed at efficient loudspeakers, and Line Magnetic's own horn models such as the Analog Sound AS-8 fall into that group. Choosing among the three output taps lets owners suit the output transformer to each speaker's rated impedance. In power amplifier mode it can also be driven from an outboard line stage such as the Analog Sound AS-133 preamplifier.

Alternatives

Another integrated option in the Analog Sound range is the AS-127, a push-pull KT88 design delivering 30 W per channel.