There is no getting around it: Resolution Audio’s Opus 21 is a component stack. That’s right, a stack in the manner of those sold at big box stores by unknowing salesmen to unknowing consumers. But try not to condemn the Opus 21 through guilt by association. This particular stack might be different. And stacks, as a concept, may not be all bad.
Consider, for instance, the matter of stacks as a pure packaging scheme. It turns out that they have a lot going for them. They don’t require a hand truck to lug around or a divestiture to purchase. Their stylishly coordinated aesthetics beg to be showcased in an actual living space. Operationally, stacks are beyond convenient; they are near-telepathic. And while in these respects stacks resemble all-in-one boxes, in other ways they are more like separates. Stacks are flexible and modular, and can relegate sonically combative elements—like digital and analog circuitry—to separate chassis. Perhaps most remarkably, stacks have an unheard-of effect on significant others: They implore you to buy one.
Externally, the Opus 21 may be a 9.5"-wide stack; but inside it’s high end all the way. From prioritizing sonics over frivolous features, to the use of high-grade parts, to fine-tuning by ear, this is a product consistent with the best traditions of the high end.
Because the Opus 21’s design and execution is in a different league than its mid-fi counterparts, so is its price. The whole works—including a CD player, mm and mc phonostages, AM/FM tuner, integrated amp, and a control center with comprehensive digital and analog connectivity—runs $7500. While clearly not in mid-fi territory, that’s still a bargain in a world where one single-function high-end component can easily reach that sum. And many Opus 21 systems will come in for less; nothing says you have to buy the full stack.
Stacks are like Lincoln Logs; you build them up piece by piece. In the Opus 21’s case, the analogy is particularly apt since its modules actually physically interlock by means of 25- pin connectors on their respective tops and underbellies. This approach negates the need for interconnect cables, with their inherent losses, and requires but a single solder point directly to each circuit board. Analog signals, status/command traffic, and power travel between components through these connectors and along a high-speed bus. Digital signals traverse an entirely separate path in order to quarantine their noise.
Both Lincoln Log structures and stacks require a foundation. The Opus 21’s is its CD player. This module actually consists of two chassis: the transport/DAC, and the Power Center. The latter contains a power supply and large display that serve not only the CD player, but any additional modules present. Cleaving the CD player’s traditional functions makes such efficiencies possible and, again, segregates noise-generating from noisesensitive components.
Because the CD player forms the Opus 21’s foundation, it is the only module that can be deployed in a stand-alone capacity. But even in that role, it is far more than a simple source. The transport/DAC chassis includes a coaxial digital input that will accommodate any stereo PCM source up to 24-bit/96kHz resolution. That allows the player to host an external device such as an XM radio receiver, PC-based music server, or DVD player. The CD module also includes a built-in high-grade analog volume control. With these features, the player becomes all that many systems will need as their front end—just add a power amp and speakers.
Of course, if you require an amp, the Opus 21 stands ready with the S30 module. Inserting it between the CD player’s two chassis adds a sophisticated though modestly powered (30Wpc) amplifier with a transformer of its own to supplement that of the Power Center. Because the S30 is actually a full-fledged integrated amp, it incorporates a linestage, its own volume control, and three analog inputs. Thus, together with the CD player, the S30 forms a flexible three box mini-tower that requires only a set of reasonably sensitive speakers to create a complete system.
Those who require additional inputs and outputs can avail themselves of the Opus 21 family’s newest member, the XS (“Xtra Sources”) module. Slotting beneath the CD transport, the XS boasts five digital inputs, including USB. The latter permits a fussfree direct connection to a PC, providing access to whatever music might dwell therein. (See sidebar.) In addition, the XS includes a headphone amp, an AM/FM tuner, separate moving-magnet and moving-coil phonostages, two analog inputs, and yet another volume control. There are also fixed and variable outputs, the latter being ideal for driving a powered subwoofer.