Classé CAM 350 monoblock power amplifier
My mother's words echoed in my ears as I unboxed Classé Audio's CAM 350 monoblock amplifiers, and I couldn't help but smile. I've been using Magnepan loudspeakers on and off for the past 20 years, most often matching them with tube amps—VTL, for example, or perhaps VAC, Sonic Frontiers, or Audio Research. As good as these systems have been, what I always inevitably found myself wishing for was "a really good, big solid-state amp."
At 350W—or 700W into the Magnepan 3.6/R's 4 ohm load—I figured the Classé CAM 350 should be able to grant my wish. Plus, the CAM 350 is no rough-around-the-edges bruiser, but a smooth, highly sophisticated design incorporating the very latest in circuit and device developments. According to Classé, the CAM 350's design and topology were carefully optimized for speed as much as for brute-force current delivery, and reflect everything the company learned while developing their statement amplifier, the Omega.
As in the Omega, the CAM 350's amplification block uses several types of devices, and a circuit designed to optimize and combine the strengths of each. The block starts with a pair of low-distortion JFETs as an input, used for their extremely low noise and speed. Next are a bank of MOSFETs, again selected for their speed and low noise, and biased to avoid crossover distortion. However, Classé's MOSFETs of choice don't have the necessary current capacity for an amp like the CAM 350, so they're used only as a pre-driver, to feed a bank of high-current bipolar transistors—Sanken's very latest flat-pack devices, to be specific—which functions as the output stage.
Also like the Omega, the CAM 350 is a truly differential, balanced circuit from input to output. It uses 16 output devices per channel, like the Omega, but a smaller version of Classé's new UHC Transfer power-supply topography. Where the Omega is fed by a massive, 2500kVA toroidal transformer, the CAM 350 uses a smaller but still massive 1200kVA unit. The Omega operates in class-A mode up to 110Wpc and class-AB after that. In comparison, the CAM 350 runs on class-A up to 80W, then switches to AB.
What's also noticeable, when peeking into the CAM 350's insides, is the absence of gigantic capacitors. Classé's approach, enabled by recent improvements in capacitor design and materials, is to use a large number of small, fast capacitors instead of a smaller number of large ones. The rationale is simple: smaller capacitors charge and release energy more quickly, so smaller capacitors mean a faster, cleaner circuit.
The execution is enough to take an audiophile/engineer's breath away. The power transformer occupies the front half of the chassis, but the rear is filled with a stack of four horizontal circuit boards, shaped to precisely nestle in around the transformer. These boards house the power supply, input, pre-driver, protection, and switching circuits. The output stages are housed on four more boards: two parallel sets of two piggybacked boards each, situated vertically up against the rear panel, which is itself an extruded-aluminum heatsink. All of the boards are as much industrial art as electronic devices: They're beautifully laid out, with thick, heavy traces, and populated with a dazzling array of super-premium hardware.
The superb execution carries over to the outside. Everything about the CAM 350 oozes a Mercedes-like sense of class and solidity, from the ½"-thick satin-finished aluminum faceplate and softly chamfered corner towers to the stout, gold-plated speaker terminals. Hookup and operation are simple. In addition to the speaker terminals, the rear panel includes high-quality RCA and XLR input jacks for balanced and single-ended inputs, a removable AC cord, and I/O jacks for Classé's IR switching system.
The front panel, too, is simple, with only a power switch and a small LED indicating the amp's status. During startup, the front-panel LED blinks red until the unit stabilizes, at which point it switches to steady red. A fully automatic mute circuit protects the unit (and the speakers) during turn-on and in the event of unfortunate incidents such as shorted outputs. When the protection circuit is tripped, the LED switches to green, and the unit is completely muted. Turning the amp off, then on again restores normal operation.