Lamm M1.2 Reference monoblock power amplifier
But what about when the original product was so goodespecially in a field such as amplifiers, in which genuinely new technology comes down the pike only rarelythat it doesn't need updating? It would be cynical to introduce a Mk.2, then a Mk.3 and Mk.4, and so on, each iteration featuring perhaps trivial changes rather than substantial improvements, merely to pump life into inevitably declining sales figures. But without such marketing mojo, an otherwise worthy product can, in the long term, be overlooked.
Which brings me to the subject of this review, Lamm Industries' M1.2 Reference monoblock amplifier. The M1.2 was introduced in late 2003 to celebrate Lamm's 10th anniversary, and was reviewed for Stereophile in February 2005 by Paul Bolin, who thought very highly of its sound. "From their massive shipping crates to the standard-setting owner's manual, from their clean, uncluttered styling to their incredibly compelling, truthful, nuanced sound," he wrote, "the M1.2s speak to the value of getting all of the little things right. When every detail has been taken care of, greatness follows naturally."
Before Paul's review of the M1.2 was published, I had been impressed by the Lamm M2.1, a similar but more powerful hybrid design combining MOSFET output devices with a tube driver, which Paul had reviewed in April 2003, and had made a note to try a pair of M1.2s in my system. But time passed much faster than my ability to cross things off my to-do list, and it wasn't until I bumped into Vladimir and Elina Lamm at a 2011 event at Manhattan retailer Innovative Audio that I was reminded of my original intention.
"There haven't been any changes in the M1.2 Ref. since the beginning of its production at the end of 2003," admitted Elina when I asked her, which in the usual course of events would have led to my writing a Follow-Up to the original review. But after auditioning the amplifiers, and considering the fact that Lamm's 20th anniversary now approaches, I thought it appropriate to celebrate with a second full review the M1.2 Reference's longevityand hence its defiance of the laws of marketing.
The serial numbers of PB's original samples were A10291 and A10292; I performed my measurements on A10301. My 2011 samples were numbers A10551 and A10552. The price in 2003 was $17,290/pair, which by the time of PB's review had risen to $19,590/pair; the price in 2012 is $23,890/paira not unreasonable increase.
Class A class-A
Vladimir Lamm's heart seems to be warmed by tubes, considering that his statement amplifiers exclusively use them. So while the M1.2 is ostensibly a solid-state designit follows the paradigm set by Mark Levinson with the ML2 almost four decades ago in being a black-anodized aluminum box with chunky handles on the front panel and hefty arrays of vertical black heatsink fins adorning both sidesa single 6922 dual-triode tube is used to drive the six pairs of output MOSFETs.
The M1.2's two RCA input jacks are in parallel with pins 2 and 3 of the input XLRwhen the amplifier is to be driven single-ended, the unused RCA is shorted to ground with the supplied plug to minimize noise pickup. The hot and cold signal phases are each taken by short lengths of shielded cable to a Burr-Brown BUF634 chip: a unity-gain, high-speed video buffer. These chips then feed the "military grade" 6922 tube via a differential pair of JFETs; the 6922 is mounted in the center of a large, double-sided printed circuit board that runs the full depth of the enclosure under the top panel, and which features wide, heavy traces for the output-stage connections. Component quality is high, with much use made of Dale metal-film resistors, Electrocube and Roederstein film capacitors, Bourns multi-turn trimming potentiometers, and Hammond filtering chokes.
The output stage is biased to run in class-A up to the amplifier's rated power. As the necessary bias current will depend on the load impedance, hence the current drawn at maximum power, a rear-panel switch selects between the appropriate bias for low-impedance speakers, labeled "16 ohms," and high-impedance speakers, labeled "816 ohms." Both this switch and the main power switch have "pull to use" toggles, to avoid accidental operation, and a red LED shows which bias setting has been selected. Each MOSFET stands on a 0.39 ohm wire-wound resistor. There is a voltage drop of 236mV DC across this resistor in "16" mode, implying a total bias current through the six complementary pairs of MOSFETs of 3.6A. In "816" mode, the voltage drop across each resistor was 175mV, implying a total bias current of 2.62.7A.