Integrated Amp Reviews

With its high-end heart and home-theater brain, Chord's powerful CPM 3300 integrated amplifier ($9500 with the aluminum-cylinder Integra leg option, $8950 without) is a uniquely fascinating audio product well worth considering. High-tech innards and magazine-cover good looks don't hurt either, but what originally got me interested was the superlative sound Chord products have consistently delivered at trade and consumer shows when paired with Wilson-Benesch loudspeakers.

Those combos always seem to produce exciting and, to my ears, musically honest sound from familiar demo discs, including CD compilations I've made using the Rockport System III Sirius turntable. A journalist has to keep moving at such shows or the coverage will suffer, but when I hit the Chord/W-B room, I inevitably end up sitting through and reconnecting with some overfamiliar demo disc in its entirety.

Game Plan
While Chord's penetration of the American audiophile market has so far been modest, the company's consumer line is expansive: preamplifiers, two- and multichannel amplifiers, DACs, and phono sections. According to John Franks, Chord's chief designer, artists including Paul McCartney, Ray Charles, and the Wu Tang Clan use amplifiers from Chord's professional line in their studios. Well-known venues include Abbey Road studios and London's Royal Opera House, which uses them for sound reinforcement.

I'd recently reviewed Musical Fidelity's M3 integrated amp (Stereophile, February 2001), so Chord's new variation on that theme seemed like a good model to choose from the company's long lineup. Like the M3, which combines much of the circuitry of Musical Fidelity's Nu-Vista preamp and 300 power amp in one chassis, the CPM 3300 is based on two extant and well-received Chord products: the C3200E preamplifier and 1200B amplifier. While twice the M3's price, the CPM 3300 actually offers somewhat less RMS power (220W vs 275W) into an 8 ohm load. I was curious to see and hear how Chord felt it could justify the CPM 3300's seemingly steep price.

Audiophiles comforted by the straightforward operating systems of most high-end audio products—turn on, select input, adjust volume—will be surprised and perhaps confused by this model's complexity. While the CPM 3300 is on the surface a simple, two-channel integrated amplifier, lurking beneath its smooth aluminum skin is a microprocessor-controlled environment somewhat like a home-theater receiver, complete with dual signal buses for independent tape monitoring, source-controlled gain settings, and dual outputs. The last allows you to route the signal to the built-in amplifier or to a set of RCA jacks for external amplification—or to both, should you choose to biamp your speakers.

Complementing the home theater-like operating menu are the two usual rancid side dishes: inadequate and confusing instructions. a complete lack of labeling of the rear-panel input and output jacks (though a key is included with the handbook) and a remote control from hell (neat, unlit rows of same-sized, multi-function buttons). If you've ever read one of my reviews in Stereophile Guide to Home Theater, you know that I readily admit to possibly having a learning disability when it comes to operating remotes. There were times when I got no sound at all from the CPM 3300 and couldn't figure out why.

The instructions emphasize the CPM 3300's capabilities while neglecting to tell you clearly how to access them (especially regarding the remote control), or in what order. The how-to section is long on jargon-filled lists and short on user-friendly prose.

I'm told that the instructions are being revised and that a new remote, designed just for the CPM 3300, will replace the impressive-looking but unwieldy and button-crowded one supplied with the review sample, and which can control up to six Chord audio and video products, your lawn sprinkler, your garage door, and probably your home's thermostat.

Design
Despite its complexity and the impressive amount of power it can deliver, the CPM 3300 is surprisingly light and compact, thanks to the switching power supply at the core of Chord's approach to building amplifiers. Designer John Franks came out of the aerospace industry, where such lightweight, compact designs are a necessity. Switch-mode supplies have been used in audio with varying degrees for years, beginning, I believe, with Bob Carver's much-vaunted The Cube amp, back in the early '80s. [Sony released an integrated amplifier with a switch-mode supply in 1979, if I remember correctly. Many in Linn's current range of amplifiers use such supplies, and they are now ubiquitous in PCs.—Ed.]

In conventional power-supply designs, a heavy transformer, rectifiers (silicon diodes or tubes), and large filter capacitors are used to drop wall voltages, convert alternating current to direct, and store energy needed by the amplifier to reproduce music. Unfortunately, according to Chord, the demands are so great that these supplies must be large and heavy, and in the best of them, efficiency in the audioband is relatively low.

In Chord's view, these bulky, inefficient designs are sluggish, put distortion back on to the AC mains, and can add noise. Countering Chord's view are all of the fabulous-sounding (if bulky) amplifiers that use just such old-fashioned power-supply designs. As with everything else in life, greatness is a matter of both design and implementation—a proposition with which Chord's John Franks would probably not take issue. It took him 10 years to overcome such problems in the audioband power supply as switching noise, poor reliability, and high costs before he felt his first amplifier design, the Chord SPM 900, was ready for the High End, in 1989.

Chord's current power supply, the fifth generation, is common to all of the company's amplifiers (in 600W, 2kW, and 4kW sizes, depending on application). This supply is a self-contained, self-monitoring module that Chord claims is extremely well-shielded and immune from interactions with the AC mains at one end and the amplifier circuitry at the other. Incoming AC is filtered and rectified to produce 300-350V DC, which is stored in high-voltage capacitors. High-voltage MOSFETs running at 80kHz "chop" the DC, which is then passed through an HF transformer. The higher the frequency, the smaller the transformer can be compared to the standard 50Hz or 60Hz design.

There's another rectification stage, a Dynamic Coupling system, and, finally, a bank of high-voltage storage capacitors. Dynamic Coupling keeps the supply's positive and negative rails tied together via a strong magnetic flux. When there is a demand for power on one rail, it is drawn from both, which keeps the system in balance so the zero crossing point doesn't get pulled one way or the other.

The CPM 3300's output stage runs in a "class-AB sliding bias design," which operates in class-A (always on) in most normal situations, and switches to class-B only in situations that demand high power. The output devices are custom-built, dual-chip 200V/300W MOSFETs; Chord claims that these ensure "perfect thermal matching," eliminating the need for temperature-balancing resistors for improved efficiency and stability.

Output protection is based on the Dynamic Coupling circuit. When the system senses flux-density differences between the two rails over time, an algorithm determines whether the cause is a need for power, or a fault such as a short circuit or a speaker-damaging DC offset. If it's a fault, the CPM 3300 switches itself to standby mode.

The preamp section is fully balanced dual-differential with a combination of balanced and single-ended inputs that are converted to balanced, though other than its output stage, the power amplifier section is single-ended. The volume and balance controls are four-gang motorized ALPS potentiometers. Each preamp channel has its own independent power supply, as do the microcontroller and the 32 hermetically sealed relays.

Connection, Operating Features, and (Ab)use
Connecting inputs and outputs is straightforward: two Disc inputs offer single-ended and balanced operation, and there are four more single-ended inputs, two of which are tape loops associated with a pair of tape outs. There are also RCA-jack line-level and speaker-level outputs. All jacks are high-quality, gold-plated chassis mounts, and the speaker-level outs are high-quality WBTs. Vinyl playback requires an outboard phono section.

On the front panel are solid brass Volume and Balance pots, a power switch (Standby/On), three buttons marked S, B, and A, and a custom blue fluorescent display. The hard-to-see slots on the rotary Volume and Balance controls make it almost impossible to gauge starting positions until you move either one, in which case the screen display kicks in. Unfortunately, while moving the balance control one way or the other causes arrows to appear on the screen letting you know in which direction you're going, there's no indication of when you've reached equal output in both channels. This will create high anxiety for anal-retentive audiophiles.

When I switched the unit on (this can't be done via the remote) I was greeted by one of the coolest cosmetic displays ever seen in consumer electronics: the outlines of the amp's innards, visible from a circular top grate, began glowing black-light style, resembling (depending on your history): 1) a 1960s head shop, 2) a night landing in Dallas, or 3) Tron. The light show is courtesy 160 tiny blue LEDs plus a few red ones, each the size of a grain of sand.

Once you're mesmerized by the lights, the fun begins! From the remote or the front panel you can choose the A or B button to select which bus you want to listen to. Bus A is connected to Tape 1 Out, Bus B to Tape 2 Out. Tape 2 In can be selected only with Bus A and Tape 1 In only with Bus B. The purpose of this ball of confusion is to allow you to record and monitor two different sources simultaneously. It's not that difficult once you understand it, and when listening to non-tape sources you can ignore it, but really—how many audiophiles need dual simultaneous analog-domain recording and monitoring? Or even single? Even digiphobes like me are mostly recording to CD and MD these days, which makes standard tape monitoring (listening off the playback head) moot.

In any case, it's there if you need it. But if you're just using one tape deck, you might as well connect it to Tape 2 so you don't have to change to Bus B just to listen. I hooked up an open-reel deck to Tape 1 and couldn't get any sound from it because I was using Bus A. I know—when in doubt, read the instructions. My advice with the CPM 3300: Read the instructions even if you're not in doubt.