Integrated amplifiers — Line Magnetic Audio LM-845IA

The LM-845IA is a stereo tube integrated amplifier from Line Magnetic whose single-ended output stage works in pure Class A on the 845 direct-heated triode. Every unit is assembled by hand and wired point-to-point, and the package includes an infrared remote control and a metal tube guard cage that lifts off.

Key specs that matter

Continuous output is 22W RMS per channel into 8 ohms in Class A, which corresponds to 13.4dBW. Total harmonic distortion is 1% at 1kHz and signal-to-noise is 87dB A-weighted. The original US list price was USD 4,895, and in Thailand the amplifier was offered at THB 146,800. Frequency response covers 10Hz to 50kHz within 1.5dB. Input sensitivity is 220mV and input impedance is 100k ohms. Power consumption is 320W. The chassis measures 365 x 250 x 340mm and weighs 35kg.

Engineering and use context

Seven valves are used in total. Two 12AX7 tubes form the input stage, two 6P3P tubes work as drivers, and two 845 triodes make up the power stage, one per channel. A single 5AR4 valve rectifier supplies the high-voltage rail. Line Magnetic uses EI cores for both the mains transformer and the wide-bandwidth output transformers. An ALPS potentiometer sets the level, and the capacitors come from Realcap. Some units have also shipped with 6L6GC driver valves in place of the 6P3P, together with ECC83 input tubes, and the chassis is finished in gloss black with the 845 tubes on view. Output tube bias is simple to monitor and trim thanks to an ampere meter mounted on the top panel. A SoftStart system with a 30-second time-delay circuit holds back the high voltage at switch-on so the valves reach operating temperature before they are loaded.

Pairing

The rear panel offers three RCA line inputs for sources such as a DAC or phono preamplifier, plus one pre-in input for connecting a separate preamplifier. Loudspeakers connect to two sets of screw binding posts that work with banana plugs, and the output transformers have taps for 4, 8 and 16 ohm loads, covering the common nominal speaker loads. In the Line Magnetic integrated catalogue the LM-845IA sits next to models such as the LM-88IA, the LM-150IA and the LM-845 Premium, which also uses 845 output triodes.

Alternatives

Line Magnetic also offers the LM-805IA, a single-ended integrated amplifier using 805 output triodes rated at 48W per channel.