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Positive Feedback ISSUE 8
august/september 2003


John Curl’s Finest? Parasound’s Halo JC-1 amplifier
as reviewed by Max Dudious


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Srajan Ebaen, in a recent column (Auroville 18; Positive-Feedback Online Issue 7) suggested that good audio writing is very hard to maintain at a high level. As it has taken me a half-dozen drafts to achieve this state, I sadly agree and I’d add, writers often suffer a form of burn-out from describing the sound of one product nearly identical in many respects to its nearest competitor, but for nuances. "The devil is in the details," as someone (Mies Van Der Rohe?) once famously said. This is particularly true when describing the virtues of one excellent amplifier as compared with others. I’d say it is the nuances one amplifier is able to recreate that separate it from its competition, or, "The devil is in the nuances." The Oxford English Dictionary defines the word nuance as: 1) a slight or delicate variation or difference in expression, feeling, or opinion; 2) a shade of color; a slight difference or variation in shade or tone; and 3) a delicate gradation in musical expression. The latest John Curl offering, Parasound’s Halo JC-1 amplifier, is among the most precisely nuanced amplifiers I know, able to draw the slightest and most delicate of musical expressions, to make the subtlest distinctions. It can also rock you, like your back ain’t got no bone, 'cuz it’s a brute. It is the amp for all seasons.

If you are a quester on the path toward the finest sound you can personally own, then you must consider owning John Curl’s latest JC-1 amplifier. It measures and performs stunningly well. It has those "magic" qualities that differentiate the best of breed from the also-rans. It has the ability to produce a believable facsimile of spaciousness, that 3-D sound-staging that makes the illusion of space between the instruments nearly tangible; the ability to produce timbral, harmonic, and dynamic accuracy that results in what we call "inner detail"; the ability to produce delicate, refined, purity of tone one moment, and then bowl you over with A BIG WALL OF SOUND the next. Parasound offers the JC-1 at a much more manageable price ($6000/pr) than you might expect, for an amplifier of the highest class. (See Srajan Ebaen’s Auroville 17 for an idea of how first-rate gear can be built at reasonable prices.) And, all in all, it is a consummate achievement of design, layout, voicing, and fit 'n’ finish.

Having said all that in the first two paragraphs I should pack my bag and go home, but my enthusiasm for this piece insists that I continue. Audio heads seem to agree: at the various classes and price points there is relatively little that separates one excellent piece of audio gear from the next. One top-flight amp might feature clarity and an abundance of inner detail, while its rival might have less of these but a more palpably liquid midrange. Another might have great sound staging but be a tad shy on bass: yet another might have big bass but a small sound stage. Selection often involves evaluating such tradeoffs as might optimize our individual systems. In my system the JC-1 amp has the delicacy of the best tubed pieces and the control of the best transistorized pieces. It seems to handle everything with the fewest tradeoffs, and with an ease I’ve seldom encountered.

As the performance of a piece of classical music by orchestra A, under the baton of conductor A, must play the same notes as the same piece by orchestra B, under conductor B; yet the first leaves us with the blahs, while the second lights up the synapses in our pleasure centers; we ask ourselves, "How can this be?" And we conclude there is little difference between the two conductors’ readings and their performances; only some minor variations in how the conductors can mix up fast/slow, loud/soft, foreground/background, and what we call "phrasing." But these "little differences" are all the difference in the world. These differences are those between very good, excellent, and great musical performances.

So it is with amplifiers. After listening to Parasound’s Halo JC-1s for too short a time, I feel I can safely report to the Positive-Feedback Online readership that these amps are truly outstanding, among the best I’ve ever heard, and the best I’ve had in my system. They distance themselves from nearly all amps in their price class and catapult themselves into the highest echelons of the best that audio has to offer. They exhibit great loud/soft differentiation, going from softest to loudest in an eyeblink, without expanding or contracting the sound field. This quality is often the result of a well designed and executed power supply and its regulation. The JC-1s differentiate foreground/background in sound-staging; rearmost instruments of the orchestra do not move suddenly to the frontmost row. In other words, the farthest instruments stay in their correct spatial arrangement as they play louder. This sonic quality is often the fingerprint of parts matching and local voltage regulation. The fast/slow relationships are maintained by the high damping factor: in many lesser amps the low notes "ring" making it seem like they are always playing "catch-up" with the mid-range notes. The JC-1's low notes are time-appropriate, starting and stopping without extending the pulse, and this freedom from ringing is a function of parts selection and avoiding parts known to ring, like cheap capacitors. Neither do any of the mids or highs ring (or sizzle, sometimes due to cheap resistors). As a consequence, all the notes are reproduced in a manner that is electronically correct and audio-optimized, and that allows for greater verisimilitude to live music. In short, the JC-1s manage to produce a more "live, in-the-room" illusion than any other amp I’ve had in my stereo system.

Since I’ve had the Parasound Halo JC-1s in my big rig, I’ve had a handful of curiosity seekers pop in—old hi-fi buddies, some new audiophile friends, some neighbors (symphony orchestra musicians)—and like the parable of the blindfolded wisemen in a room with an elephant, each reports back what he experiences. The one who feels a leg says he must be in a northern forest. The one who feels the tail says he must be in a tropical jungle or somewhere where heavy vines grow. The one who feels the stomach says he must be in a stone quarry.

Usually the audiophile concentrates on that part of the frequency bandwidth to which he’s most sensitive. One friend with deep pockets, whose credentials are that he’s owned about a dozen big-time systems over the past twenty-five years, Jim Rittler, said, "The mid-range is extraordinarily clean and musical." Another audio hobbyist, a little new to the quest, a savvy inside the D.C. beltway type, Steve Sokolow, said, "The bass blows me away." (Newbies are always impressed by big, clean bass.) A TV journalist, an audio/video guy with C-SPAN, who goes to the C.E.S. shows as part of his professional responsibility, Paul Loeschke, said, "The best system I’ve heard—owned by a private party." I guess he meant not a system set up for shows, which only a very few of us can afford as they now measure in the hundreds of $Ks. Another audiophile, my neighbor and a symphony bass violist, Erik Stahl, said, "The string tone is natural, with a nice balance of woody tones and brilliance, without the usual wiry quality of most systems." Each of these auditioners were familiar with my system in the evolutionary state that preceded the JC-1s. I haven’t conducted this informal test with the rigors that would satisfy the current requirements of the National Science Foundation, so I’m not sure, but I’d venture to say the raves were likely due to the JC-1.

If you are a quester with a wife and kids, you’ll know family members usually react as tactfully as they can, trying not to offend your obsessive streak after you’ve installed the latest widget in your system. "It always sounds so good, Dear (or Dad). It sounds more or less like it always sounds, only a little better," spoken with a sweet smile. With the JC-1s online, my wife, daughters, son-in-law, all concurred: something new had obviously improved the sound a large notch, especially as regards clarity and detail. I’m astonished. I can hear everything! Even in music I thought I knew," was the frequent line of comment, without the "grin-fuck" at the end. Getting such flattering feedback from family members is like pulling teeth, so something striking must have happened to their audio perceptions. What happened was the JC-1s. And in the same way that each of the blindfolded "wisemen" feeling the elephant was correct, as far as he went, each of my family and test panel "wisemen" was correct. The highs were silkier, the lows were more robust, the mid-range was drop-dead gorgeous, the clarity and detail were stunning, and I’d add, all of this was presented in a most relaxed fashion. In fact, in my listening room the relaxation quotient was so palpable, you could cut it with a knife.

How could this happen? After concluding his testing of Parasound’s Halo JC-1, John Atkinson wrote (in Stereophile, February 2003, p. 79), "This is excellent measured performance. The Halo JC-1 is not only the best amplifier to come from Parasound, it ranks up there with the best high-end heavyweights." Michael Fremer added (on p. 83), "measured performance doesn’t always correlate with actual sound, but in this case, assuming the Parasound Halo JC 1's published specs resemble what John Atkinson measures, there’s a strong connection. The specs show ultra-wide bandwidth, high-current capability, low, low noise, a high signal/noise ratio, and a fast slew rate, among many other indicators of outstanding amplifier performance." And Sue Kraft (in The Absolute Sound, Issue #142, June/July 2003, p. 87) described that performance as follows: "Although Parasound recommends a minimum 30-day break-in period, I was impressed with the remarkable speed, clarity, transparency, and focus of these amps straight out of the box. I found the overall sonic character to be fairly neutral, with a pace, rhythm, and effortlessness that was absolutely addictive." It seems the professional experts agreed with my panel of amateur experts. This is one hell of an amp.

How did this come to be? You might learn more by reading the articles cited above in their entirety, and there is an account of the development of the amplifier that is to be found on-line at the Parasound web-site; For you lazy bleeps, I’ll say this amp has been the joint effort of four men: designer, John Curl, who has been incrementally improving his basic circuit design for years; parts specialist, Bob Crump, who hears the difference between parts of the same value produced by different manufacturers; layout specialist, Carl Thompson, who optimizes performance of parts on printed circuit boards by optimizing their physical placement, minimizing interactive fields (a kind of crosstalk), ground-loop hum and such; and Parasound’s CEO, Richard Schram, who is known for having solved many of the riddles of off-shore production, and has dedicated the resources of his company "to create one of the great power amplifiers of all time, a totally uncompromised 'best in category’ product that would still be reasonably priced." (From his letter to the editor published in The Absolute Sound, June/July, 2003, p 121.)

In audio, I’ve noticed, reiterations of the same design are one of the ways designers get to optimize the performance of speakers, amps, etc. Sid Smith made numerous Williamson-type amplifiers before he designed the Marantz 8B, and then (for the next thirty-five years) he worked on a series of modifications that would keep it up to date. The current iteration of the Vandersteen 2CE Signature looks like a much refined version of the three-way he offered in the '70s. The Cary 805C amplifier is a refined version of the Cary CAD-805 that debuted ten years ago. The list gets very long when you think of gear that is periodically refined or upgraded. Parasound’s Halo JC-1 is John Curl’s most recent iteration of a topology he’s been working on for fourteen years, off and on.

In 1989 Richard Schram commissioned John Curl to re-design the Parasound HCA (High Current Amplifier) 2200, a generic 220 watts/ch amp with a shared power supply, and turn it into a high-performance piece. The Parasound HCA-2500 (250 wpc) followed soon after, a kind of HCA-220 "on steroids." It featured more output devices, higher voltages, more heat sinks, an improved power supply, but it had the same power amp topology Curl had been using for a while: a complementary J-FET input stage, followed by two stages of hand selected push-pull MOSFETs, driving the output stage. It served as an in-house interim prototype, and Parasound never offered it to the public, because the next iteration so strongly insinuated itself.

Curl soon designed the Parasound HCA-3500 with a "stiffer" (no voltage drops or sags on peaks) dual mono power supply (each half of the transformer had its own AC line), more filtering capacitance, still more output devices, more finned heat sinks, and he bumped its output up to 350 wpc. It remained the same circuit in terms of block diagrams and circuit topology, only with better parts, more regulation, and it was all on one chassis. The HCA-3500 turned out OK, but wasn’t outstanding. How did it get so good and rise, like the Phoenix, from its own ashes to become the JC-1? You might ask.

If you’re asking, I’m telling. Of course as with most writers I’m always seeking to find the narrative thread in a bunch of facts. I apologize to any historians among you for emphasizing the storyline over documentation of names and dates, but I’m a frustrated epic poet. After the lukewarm reception of the HCA-3500, Curl got together with Bob Crump and Carl Thompson, formed CTC Builders, and began doing modifications to the 3500 on a subscription basis, turning them into the impressive "BBQs." They also made (and still make) their no-holds-barred "Blowtorch" pre-amp on a one-off subscription basis, which enjoys a cult following among perfectionists. Along the way, creating a series of successful reiterative modifications (or pooges), Curl, Thompson, and Crump (the CTC of CTC Builders) got the 3500 to sing. They presented a fully re-constituted (or pooged) BBQ to Richard Schram for evaluation, and he gave them the go-ahead to develop a pair of JC-1 prototypes for evaluation. I can only imagine the CTC Builders’ reaction when Schram told them he wanted the new amps to be separate chassis monoblocks. It is seldom that designers get that kind of support from their boss.

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With this mandate, Curl decided he would use a larger 1.9 kVA encapsulated toroidal transformer and 132,000 microfarads of filter capacitance. This base increased by 100% the already pretty "stiff" power supply of the BBQ for a meager 12% increase in watts per channel to 400. The power supply was beginning to approach the "Mother of all Power Supplies" category, claiming a current capacity of 135 amperes on peaks. Not that brute force is everything. Bob Crump insisted on using Harris hyper-fast soft-recovering diodes in all the bridge rectifiers in the main and local supplies, for finesse. They claim a slew rate greater than 130 V/µsecond.

While increasing the number of output devices by only one pair, the amount of chassis surface assigned to heat sinks went up 40%. These finned aluminum heat exchangers (like those on motorcycle engines) are important when running the amp in the "hi-bias" setting that insures at least 25 wpc of pure Class A power. In "lo-bias" mode, the JC-1 delivers only 10 wpc of Class A before it goes into Class B mode. Running "hi-bias" adds 3 or 4 more dB of Class A, which causes the amp to run significantly hotter. These amps like to have summertime air-conditioning in my mid-Atlantic climate. If your electrical system can’t handle both your AC and your audio system, a dedicated fan might do. Thermal conditions are a concern, but if you are contemplating a pair of JC-1s, at $6000, you probably enjoy an air-conditioned lifestyle. We know our readers have somewhat, if not infinitely, deep pockets. Right?

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Schram likewise chose to go all-out in audio-optimum parts selection, and it was Crump’s job to "voice" the amplifier (as a piano tuner voices a piano to sound more "pearly" or more "steely" by using lower or higher density felt on the hammers), yet stay within a reasonable budget. Crump saw to it the parts list read like a who’s who of quality manufacturers: Vampire Direct gold-plated Oxygen Free Copper RCA connectors (my favorite, least colored), Neutrik XLR connectors, Reliable RT DC bypass and Zobel capacitors, Superior Electric binding posts, Vampire continuous-cast-copper signal and DC wiring (another of my favorites), Nichicon Great Supply raw DC capacitors (another proven manufacturer), Nichicon Muse DC and local bypass capacitors, Harris diodes (already mentioned), and Sanken output transistors (another trail blazer). Somehow Schram is able to see to it that these parts arrive at the factory, that only these specified parts are used in production, and that there are checkpoints and batch checks to insure high quality control throughout production. The result is an amplifier with excellent build quality, audio optimum parts, and ear-opening performance.

How could the JC-1, with the same circuit topology as the previous iterations of amps coming from Parasound and Curl, sound so much better than its close relatives? My best guess is, "Everything matters." That is, since everything is interconnected, a slight change in a part’s value, or in a part of the same value but from a different manufacturer, or a part of the same value from the same manufacturer but a different batch (using a different production technique), can change the voice of an amplifier. I’m not sure I believed that until Curl got me to change one resistor in the feedback loop of each side of my Parasound 3500. With a bulk film (Vishay-type) resistor the sound was dry and etched, but with a foil on glass (Holco-type) the sound got warmer and more natural. We’re talking about one part in a critical spot. Think of all the parts in such an amplifier.

Curl once explained to me that when the design of his power supply for the BBQ was frozen, and Crump’s selection of parts was nearly-so, they still couldn’t understand why the prototype’s sound wasn’t as optimal as it promised on paper. It was then the Curl called in Carl Thompson to do his work on laying out the parts on the front-end circuit boards. Thompson enjoyed the reputation of having some intuitive sense (beyond computer modeling) of how to get rid of hum and other undesirable noise, and how to keep the hand selected parts from "talking to each other" in an undesirable way. When I spoke to Thompson about this stage in the design he said: "I’d verbalized some thoughts to Curl, and in a matter of a few days he’d devised some new ways of making very sophisticated low-level measurements addressing themselves to my concerns." Together, Curl and Thompson managed to clean up the front end, and soon the design of the BBQ was frozen. When the time came to design the JC-1, they had already done most of the important work on the front end boards, and it was just a matter of some small adjustments.

One might ask, on what basis did Curl "voice" this amplifier? I think that would be fair, since this review is somewhat a meditation on nuance, and voicing is a good example of it. In my late-night telephone gab-fests with Curl, he repeatedly mentioned a book: Science & Music, by Sir James Jeans, Cambridge University Press (1937). Reprinted by Dover Books (1967), Science & Music is available at most of the usual vendors. I got myself a copy. On page 86 Jeans writes:

The timbre depends only on the relative energies of the various harmonics and not on their phase-differences. Differences of phase produce no effect on the ear. This is known as Ohm’s law, having been discovered by G.S. Ohm (1787-1854), the discoverer of the still better known electrical law.

The second harmonic adds clearness and brilliance but nothing else, it being a general principle that the addition of the octave can introduce no difference of timbre or characteristic musical quality. When the second harmonic is of equal strength with the first, it produces much of the same effect as adding the octave-coupler on an organ or harmonium or playing in octaves, instead of single notes on the piano.

The third harmonic again adds a certain amount of brilliance because of its high pitch, but it also introduces a difference of timbre, thickening the tone, and adding to it a certain hollow, throaty or nasal quality, which we may recognize as one of the main ingredients of clarinet tone.

The fourth harmonic, being two octaves above the fundamental, adds yet more brilliance, and perhaps even shrillness, but nothing more, for the reason already explained. The fifth harmonic, apart from adding yet more brilliance, adds a rich, somewhat horn-like quality to the tone, while the sixth adds a delicate shrillness of nasal quality.

As the table on p. 73 shews, all these six harmonics form parts of the common chord of the fundamental note, and so are concordant with this note and with one another. The seventh harmonic, however, introduces and element of discord; if the fundamental note is c, its pitch is approximately b , which forms a dissonance with c. The same is true of the ninth, eleventh, thirteenth, and all higher odd-numbered harmonics; these add dissonance as well as shrillness to the fundamental tone, and so introduce a roughness or harshness into the composite sound. The resultant quality of tone is often described as "metallic", since a piece of metal, when struck, emits a sound which is rich in discordant high tones.

What John Curl reads in his solitary nocturnal reflections, or private research about music, though dated, is still illuminating: it demonstrates how the acoustics of musical instruments can be exaggerated by electronic circuits unless proper steps are taken to avoid undesirable "roughness," "harshness," and "shrillness," apparently due to odd-numbered harmonics in the signal path. Apparently, Curl has taken special pains to minimize these devils. The result is that the JC-1 is "voiced" toward emphasis on even-numbered harmonics, which is characteristic of the best tubed amplifiers. Or, we might say, Curl has designed this amplifier with a design goal of approaching the sound of good tubed amplifiers, along with the authority of the best solid state amplifiers. I’d say that in large measure he has succeeded! And that’s why in certain circles, the guy is a legend.

How does it sound? I thought it sounded pretty good, and the best comparison I could devise was an A/B listen against my trusted Marantz 8Bs. I hadn’t had the 8Bs in my big rig in a while, and I was interested in how they would sound. So I got them out, re-biased the output tubes, and installed the amps. They are much modified, according to Sid Smith’s instructions, and sometimes with his hand on the soldering iron. They are each bridged to mono, run EL-34s in triode, push-pull, and measure just about 40 watts output into 8 ohms. As there are two such amps, as there are two JC-1s, swapping them in and out wasn’t so tough.

In a comparison at a friendly shop some years ago, a similar pair of much Sid Smith modified Marantz 8Bs sounded a lot like the Cary CAD-805 amps, in an A/B "shootout" on Quad 63 electrostatic speakers. If what is left of my memory serves me, the Cary is a single ended triode design using the 300B tube as the driver, and a 211 tube as the output, while the Marantz is a push-pull design, using EL-34s running in triode. Where the Cary 805 had a very plummy and rich sound in the lower and middle mid-range, the Marantz 8B was noticeably leaner; where the 805 had a somewhat looser bottom end, the 8B was tighter; and, where the 8B had a clean and extended high end, the 805 seemed splashier and more sibilant. Though they were actually close, the 8Bs had more control over-all, with a midrange that had noticeably less even-order harmonic coloration than the Cary. My audio buddy, Dr. Ijaz Khan, was also present as an ear-witness to the "Shootout At The Audio Corral." At the time, the heavily pooged Marantz 8Bs seemed a perfect match for electrostatic speakers such as the Quad. Though I could see how the Cary could be described as a "luscious" amplifier, especially on female vocalists, I thought the Marantz was more "neutral."

Remembering how well, in a relative way, the Marantz 8Bs did in direct comparison with the Cary 805s, I was a little hesitant to put them up against the JC-1s. What might be revealed? Maybe the 8Bs would be flatter, better controlled? It came as small surprise that the Parasound Halo JC-1's performance would best the Marantz in most categories: the bass was more robust and better controlled; the highs were even sweeter and more extended; while the mid-range was similar in kind but had more control at high volumes which allowed the JC-1s to sail through those densely orchestrated passages with significantly greater ease. That relaxation in presentation again. The tonal quality of the middle frequencies was so similar, it was hard to tell them apart on some solo passages of one instrument or vocalist. I agree with The Absolute Sound’s reviewer, Sue Kraft, who wrote of the JC-1s, "If there was any error here at all, it was to the forgiving side. The high frequencies were to-die-for silky smooth, crystal clear, and abundantly detailed." Again, I concur.

It might not be fair to compare a mid '50s design of a tubed amplifier, with a paltry damping factor and slew-rate, to a modern solid-state amplifier with state-of-the-art specs in these regards. If you think of the Marantz 8B amplifier as a "dedicated" electrostatic speaker amp, and you think of Parasound’s Halo JC-1 as a "dedicated" cones and domes amp, you might see how comparing them might be like comparing apples and oranges. But I was eager to hear how tubey the modern transistorized amp might sound, with its stated design goal to knock back odd-order harmonics. And I was eager to hear how Sid Smith’s Williamson-type amp might sound, with its design goal to employ the best modern passive parts, and regulators, to his time-honored 8B circuit topology. In many regards, the two start to converge sonically. The 8Bs are not as euphonically colored as the 805s, moving away from what we’d have called "typical tube sound" only a few years ago. The JC-1s have moved away from the two-dimensional sound stage, and the etched character that we’d have called "typical transistorized sound" a short time ago. While they are not a direct match, the two amps do sound alike in many ways: sweet highs, liquid midrange, lots of air and space around the instruments, and great soundstaging.

John Curl seems to have achieved his design goal of achieveing the best of both tubed and transistorized sound. Bob Crump’s contributions in voicing the amplifier seem to match my expectations of what great audio can do at its best. Carl Thompson has kept Crump’s chosen parts in optimum performance range by placing them judiciously on the printed circuit cards. Finally, Richard Schram’s judgment of the viability of this project has been upheld by the excitement Parasound’s Halo JC-1s have generated in the audio community. "Good job" to all concerned. "Good job."

If you’re in the market for a top-quality amp, now hear this. Go to a dealer that carries the Parasound line and audition these amps. Even if you’re not in the market, but you’d like tohear what all the fuss is about, go audition these amps. To know what the rest of the field ought to be aiming for, go audition these amps. Take your most familiar CDs and you’ll be surprised. In case you haven’t caught my meaning: go audition these amps. They may be the biggest bargain in high-end performance. If you’re a nut like me, you might threaten your domestic tranquility over these honies.

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