Предусилители — Audio Note M5 Line

Audio Note UK builds the M5 Line as a valve preamplifier for line sources, graded at Level 3 in the company's system for classifying its products. The M5 platform is sold as M5 Line, M5 Line Balanced CD Input, M5 Phono, M5 Phono Balanced CD Input and M5 RIAA, and the Line version has no phono section. Its power supply is derived from the Galahad supply of the brand's M10 preamplifier.

Key specs that matter

Four line inputs on RCA sockets are fitted, plus a tape loop whose return can act as a fifth source. Input impedance is 100 kohm, and 126 mV at the input produces 1 V at the output, while gain is 18 dB. Output impedance stays below 10 ohm, and unweighted output noise is under 80 microvolts. The chassis is 140 mm high, 440 mm wide and 410 mm deep and weighs 16 kg, with a maximum consumption of 81 W. Owners can order a black acrylic front or one in anodised aluminium.

Engineering and use context

Audio Note specifies pure Class A operation, a single-ended circuit with no negative feedback and valve rectification for the M5. An ECC82 and a 5687 form the line stage, a direct-coupled cascaded anode follower, and the signal leaves through a custom output transformer on HiB C-cores with copper windings. That transformer lets the valves deliver their full output into the power amplifier and interconnect, so the M5 can drive low load impedances and long cable runs, and it also creates a true balanced output without differential circuitry. In the supply, a 6X5 valve rectifier is followed by ECL82 voltage regulation and a 5651 reference stabiliser. Level is set by a stepped attenuator for each channel rather than a conventional potentiometer, and inputs are switched by a Swiss ELMA selector with gold contacts. Parts include Audio Note copper wiring, tantalum resistors, SILMIC filter capacitors and copper foil signal capacitors. A warm-up period of about 45 seconds is needed after switch-on, and the unit may be left switched on continuously.

Pairing

Two identical sets of unbalanced outputs allow bi-amplification, and an XLR balanced output feeds amplifiers with balanced inputs, chosen with a selector switch - Audio Note advises against using the balanced and unbalanced outputs at the same time. The ability to drive long leads makes it practical to place monoblocks close to the loudspeakers. Audio Note asks that the preamplifier be switched on before the power amplifier and off after it.

Alternatives

Above the M5 sits the Audio Note M10 Line, a valve line preamplifier with its own higher-grade line stage.