Audio Note M2 Balanced Phono preamplifier
Other Audio Note preamps came to call. I tried the somewhat upmarket M2 ($2695 with phono), which sounded like a more refined version of the M1. Then came the very upmarket M3 ($7500 with phono), which took all those strengths and presented them with a level of musical ease and rightness I'd never heard from a preamp before.
Now the Audio Note designers have worked their way back through their preamp line—which, incidentally, peaks out at the mighty M10 ($40,000 without phono: go ahead and wince). The M2 has come up for redesign, resulting in a product that not only nips at the M3's heels but comes close to tying the race: the M2 Balanced, or M2B.
As its name implies, the M2 Balanced can drive the balanced inputs of any amplifier so equipped (although it isn't designed for balanced throughput: all of its signal inputs are single-ended). Arguably, though, the M2B's greatest design distinction is that it speaks to the world through a pair of output transformers, just like a tube amp. That's something Audio Note has been doing for a number of years, beginning with their top-of-the-line M10.
As the company's Peter Qvortrup puts it, transformer drive "linearizes the entire dynamic envelope of the music passing through the preamp. Resistors and capacitors are imperfect in the sense that they all alter the relationship between amplitude and frequency. [But] a correctly designed interface transformer does not. It is, as the word indicates, a near perfect transformation of one voltage/current relationship to another, with minimal loss and distortion of the passing signal content." Consider also that an output transformer is a means of keeping output impedance low without additional active circuitry or, even worse, feedback. Audio Note looks at feedback the way GreenPeace looks at tuna nets.
Upstream, each channel of the M2B's line section uses a single 6922 dual triode tube (footnote 1), the two halves of each tube combined as a paralleled common cathode amplifier; their output is loaded by the primaries of the aforementioned output transformers (one for each channel), with separate secondaries for balanced and unbalanced output. The phono preamp comprises three dual triode tubes, split in this instance so that one half of each tube works for the left channel, the other half for the right. The phono input sees a cascoded 6DJ8 and 12AX7A, and the output is a 12AU7A. Between them is a passive RIAA equalization circuit.
Even further upstream, the M2B's power supply shares a family resemblance with those of other Audio Note products: It uses a rectifier tube (6X5WGT) for the rail voltages, and a traditional pi filter centered around a 20-Henry choke smooths the power. DC for the various tube heaters is conditioned with separate solid-state regulators, each done up with nice-looking heatsinks.
The M2B's interior is a much tidier place than those of the earliest Audio Note UK preamps, with a neater and sturdier chassis in particular. An enameled metal shield keeps the power supply on the right from messing with the phono and line amps on the left. Sockets for the five dual triodes all appear on the same neat board, and two narrow sub-boards in front contain the volume and balance potentiometers, plus a motor for the former and the chips and other parts for a basic remote-control system. Low-level signals travel across short lengths of Audio Note AN-C interconnect cable, which is a shielded copper Litz type, and the output trannies' secondary windings go straight to the output board, with a pair of XLRs for balanced connection and two pairs of RCA jacks for unbalanced use.
Source selection is done with relays instead of a mechanical switch, these being mounted close to the input jacks to keep low-level signal paths short. The remote handset lets the user scroll through the row of five inputs (including phono) from either direction. Volume can be adjusted using either the remote or the front-panel control, and so can the mute—but the balance can be adjusted only at the preamp itself.
You know what I'm going to whine about now: I wish the M2B had a mono button and a channel-reverse switch. It doesn't. On the other hand, its balance control, which attenuates either channel by up to 9dB, isn't bad at all: Its effect on the clarity of the M2B's sound was only barely audible. A good enough compromise.
Installing and using the Audio Note was easy as pie. The silver-plated input jacks fell easily to hand at the preamp's back, and the extra pair of unbalanced output jacks even let me take my Linn Sizmik subwoofer out for a spin. The chassis never became more than a little warm to the touch, which encouraged me to leave it powered up most of the time. Just remember: With its large, frame-type power transformer, two hefty output transformers, and a good-sized power-supply choke, this iron-rich preamp is, at 32 lbs, heavier than the norm: A flimsy little shelf just won't do.
Now that I'm done with renovations to my main listening room (new hardwood floor, built-in record shelves, a relocated door, miscellaneous cosmetic details), my listening habits have evolved (footnote 2): Rather than doing all my listening in just one room, and regularly schlepping lots of associated components in and out, I can now have two very different systems set up more or less permanently, in two different rooms. These are shaping up to be:
• one room for a low-power system built around Lowther horns
• one room for a high-power system built around the Quad ESL-989s
This happy plan has also benefited from my decision to keep the superb EAR 890 amplifier, which I wrote about in the April 2004 Stereophile: After its trip to New York City for measurements and photographs, John Atkinson shipped the 890 back to me, and I've bought it from the importer. In addition to giving me a high-power reference, the EAR and its switchable balanced inputs now allow me to comment on that mode of operation, where applicable.
Footnote 1: The original M2 was a very different thing. It had a single dual triode (6SN7) for both channels' line amplifiers, and two 6922s for phono section gain. It also had switchable global feedback, allowing the user to choose 0dB or 6dB of the stuff.—Art Dudley
Footnote 2: Attention, Georgia boards of education, this means it underwent small changes over time.—Art Dudley