Lamm Industries ML1 monoblock power amplifier
By Jonathan Scull   •   May, 2000 The last Lamm product I had my hands on was a pair of M1.1 monoblocks (see Vol.18 No.4, Vol.22 No.7). I liked those hybrid tube/solid-state amps quite a lot.

Since then, Lamm has weathered the vicissitudes of the audio business and has soldiered on to produce a full range of tube and hybrid electronics. They've also coaxed very respectable sound from recalcitrant rooms at diverse audio shows—a real miracle, I can tell you. In fact, Vladimir Shushurin, Lamm's president and director of engineering, told me they'd achieved excellent results at last year's Moscow show with a pair of JMlab Utopia loudspeakers, receiving an award for "Best Sound."

Thus it was that those devilish tiny triodes lit their filaments behind mine beady eyes, and the next thing you know...

Circuit topology and build
Visually, Lamm's 90W ML1 monoblock is a blend of contemporary form-follows-function styling with several retro-chic touches. Two huge transformers dominate the rear, and the densely potted power transformer is thick as a brick. A pair of 6C33C-B triode tubes sit mid-deck and slightly offset to the left in front of the output transformer, with two more tubes—a 12AX7 and a 12BH7—before them. Top deck right resembles a panel from a Cold War-era bomber: a vertical array of two old-fashioned circular meters with three flick-switches below. Three minutes to target...

The ML1 is hand-built with parts of the finest quality: Dale metal-film resistors; Caddock power film resistors; PRC wire-wound resistors; Bourns multi-turn potentiometers; Electrocube and Roederstein film capacitors; high-frequency switching-grade Cornell Dubilier and United Chemi-Con electrolytic capacitors; Hammond chokes; gold-plated Neutrik XLR connectors; and military-grade "low-noise, long-life" vacuum tubes. The toroidal power transformer has no mechanical contact with the transformer cover or the chassis, and is suspended in a resonance-absorbing "encapsulant."

The porky 6C33C-B is a robust, high-current output tube with, according to Shushurin, a very low internal impedance of about 80 ohms. "It's like a transistor!" he enthused. "You know, most typical audio power tubes have 300 or 400 ohms internal impedance!" (It's amazing what we all get excited about.) As he explained, this permits the use of an output transformer with a low turns ratio and extended frequency response, plus "dramatically reduced" leakage inductance.

Despite its Bomber Command meters, the ML1 is 21st Century under the skin. The 12AX7 input tube carries a Wilson current mirror based on Motorola transistors. The second voltage-gain stage, the 12BH7, is hitched to the driver/buffer stage—a quartet of high-frequency, high-voltage Hitachi MOSFETs, which means the ML1 is actually a hybrid design. "Extremely linear!" declares Dir. Eng. Shushurin. We're looking at low loop-negative feedback and about 12 or 14W in class-A before the switchover to A/B.