Parasound Halo A 21 Stereo Amplifier Review

Every January at CES I make my annual pilgrimage to the Sound Lab room to hear the latest iteration of Dr. Roger West’s M-1 electrostats, and every January I come away thinking that the M-1s are, along with the Magneplanar 20.1s, the best value in a full-range highend loudspeaker—fast, rich, life-sized, transparent, highly detailed, unbeatably coherent, and blessed with bottom-end extension like no other ’stats.

Good as the M-1s are, part of the credit for their sterling showings at CES has to go to the electronics Dr. West uses. Like Maggie, Sound Lab demo’s its speakers with reasonably priced solid-state gear, and for the past several years that gear has come from Parasound—the San Francisco electronics company that had the eminent good sense to hire John Curl to design its “Halo” line of monoblock, stereo, and multichannel solid-state amplifiers.

For those benighted few who don’t already know this, Curl is the guy who first put transistors on a competitive footing with tubes in the mid-1970s with his classic ML-1 and ML-2 amps and JC- 1 and JC-2 preamps (designed for Mark Levinson Audio Systems, back when Levinson was a Mark and not a marque). Since then he has designed many other amps and preamps for numerous highend companies, as well as making his own Vendetta Research phonostage and CTC “Blowtorch” preamp.

At CES, Sound Lab mates its M-1s with Parasound’s top-rank $7000 JC 1 monoblocks. The component under review, the $2000 Halo A 21 stereo amp, is slotted in further down the Parasound line. Nonetheless, it is still very much a Curl design, with his customary J-FET input stage, MOSFET driver stage, and beta-matched bipolar-transistor output stage—each arrayed in a complementary configuration, making for a more linear and lower distortion circuit. Both input and driver stages are biased Class A, while the output stage is biased Class A to about 10W and Class AB beyond that. Though superior build-quality is something I take for granted in the products I review in Exotica, I was genuinely surprised by the superior fit ’n’ finish of the A 21, which looks almost identical to a JC 1 and, at 60 pounds, weighs only four pounds less. With its thick uncluttered faceplate and heavy-gauge brushed steel chassis, finned at either side with heat sinks, this is one clean, hefty, handsomelooking component. The amp’s innards are just as impressive as its outers—1% resistors, polypropylene caps, doublesided FR4 glass-epoxy circuit boards, a 1.2kVA encapsulated toroidal power transformer, and 100,000μF of powersupply filter capacitance. On its back panel, the A 21 has pairs of balanced and unbalanced inputs (each with their own discrete circuitry), a strip with 24kgold- plated five-way binding posts, and volume controls for both output channels (presumably so the amp can be driven directly by a CD/SACD player, although the amp’s volume controls also allow you to match the gain of a preamp or controller to the A 21). When the amp’s volume controls are turned all the way to the right (clockwise), they are out of the circuit. With the throw of a switch, the A 21 can also be bridged for mono operation, though Parasound doesn’t recommend mono use with speakers lower than 8 ohms in impedance.

There was some talk in our Special Report on Class D in Issue 166 about how these new-technology amps stomped comparably priced older-technology Class AB amps. Well, if you want to make an apples-to-apples comparison between Class D and Class AB, look no further than the Parasound A 21. At $2k, it’s priced about the same as (actually, less than) a typical Class D entry and offers similar power (250Wpc into 8 ohms and 400 into 4), similar control (a damping factor of >1100 at 20Hz), and superior bandwidth (2Hz–120kHz ±3dB). I, for one, found the comparisons to Class D and to much pricier Class AB amplifiers enlightening.

Swapping the Parasound in for the $20k Class AB Audio Research Ref 210 tube and $40k Class AB MBL 9008 solidstate monoblocks that are my references was somewhat less of a horizon-lowering experience than I anticipated. Putting aside the usual differences between tubes and transistors, all three amps sounded fundamentally similar, and I had to listen carefully to sort out what I was hearing. Differences certainly weren’t as marked or as dramatic as, say, those between Class D/T and top-line Class AB.

Nonetheless, it soon became apparent that the A 21 did not have quite the air, sweetness, bloom, and liquidity in the upper midrange and treble of the ARC tube amp or the MBL 9008 solid-state amp. As a result the orchestral bells on the Classic/Everest reissue of The Pines of Rome were a bit less airy, open, and delicately nuanced, the London Symphony strings a little less silken in their upper octaves than they were through the two Class AB super-amps. On the other hand, the A 21 had a high end—and a quite respectably good one. Unlike the $4995 Class D Rowland 201 or the $3995 Class T ARC 300.2, its treble wasn’t rolledoff, airless, bloomless, or dead, nor was its upper midrange notably bright and aggressive or caramel-colored.

In the midband, the differences between the Class AB super-amps and the A 21 (once the A 21 was warmed up) were somewhat similar to those in the treble. In imaging the super-amps had more body, dimensionality, and air than the Parasound, so that instruments were rounder and fuller and bloomier. Largescale dynamics were also livelier and small-scale ones subtler and more fully articulated than they were through the A 21. Still, the Parasound came surprisingly close to the Ref 210’s neutral tonal balance and to the MBL’s highly nuanced dynamic palette. Where I would easily have heard the timbral and dynamic signatures of the Class T ARC 300.2 and Class D Rowland 201 in the playback of something like John Shirley-Quirk’s baritone and the Los Angeles Philharmonic’s strings, winds, and brass on the great Columbia recording of Lutoslawski’s Les Espaces du sommeil, I was harder put to hear major differences between the A 21 and the two super-amps. In the broadest strokes, and in some of the finer ones, all three Class AB amps sounded more alike than different—and to my ear more like the real thing.

As with its midrange, the A 21’s bottom end was excellent. Though not as realistically full and bloomy as the ARC tube amp or as consummately explosive, extended, and finely detailed as the MBL 9008, the Parasound, nonetheless, went deep with enough power, resolution, and bass-range air to reproduce the 16-foot pipes of the E.&G.G. Hook organ on the Mendelssohn Sonata No. 1 [Sheffield] with lifelike solidity and room-shuddering authority. Ditto for the bass-range workout provided by the contrabassoon and tam-tam on New World’s superb recording of George Crumb’s A Haunted Landscape—a record you will be hearing more about when I review the Wilson- Benesch Torus subwoofers in Issue 170. The Class D amps I reviewed were also remarkable in the bass—with particularly fine “grip” and power in the bottom octaves. That said, I don’t think any of the ones I auditioned had much of a leg up on the A 21, which not only had similar grip and power but also didn’t seem to store most of its dynamics in the bottom octaves.

The A 21’s resolution of low-level detail was across-the-board high. While not the near-world-beater that the Class D Rowland 201 was in the midrange, neither was it as euphonically colored as the Rowland. It reproduced that buried-in-the-mix snare drum in the “The Pines of the Villa Borghese” segment of The Pines of Rome clearly (though not as clearly as the Rowlands) and caught the atypical and hard-to-hear vibrato in Mary Travers’ voice on “Blowin’ In The Wind” [Warner] with admirable clarity. It did not sustain harmonics, however, with the lifelike duration of the Class AB super-amps or the Rowland 201 (which was simply remarkable in this regard), making for slightly leaner (though nothing like threadbare) timbres. Nor was soundstage width quite as broad as it was with the super-amps, though depth and layering were comparable.

I’m not going to kid you: In spite of family resemblances, the Parasound Halo A 21 is not as “good” as either of the two ten-to-twenty-times-moreexpensive Class AB super-amps. What the A 21 is is a very fine amplifier at an exceptionally fair price—more lifelike, I think, than much of its more expensive Class D competition. Bottom line: I could not only recommend the A 21 enthusiastically to audiophiles on a budget (what a combo it would make with the Maggie 1.6QRs!), but could live with it myself—in a system that costs fifty times what it does. TAS