Cary Audio Design CAD-572SE monoblock power amplifier Robert Deutsch December 1998
Single-ended triode (SET) amplifiers. Designs from the '30s, using tubes first manufactured in the '30s. Low power, high distortion, restricted frequency range. High output impedance, with consequent variations in frequency response. Oh, and tubes that cost up to $400 each. Gimme a break!
And yet...I thought there might be more to the preference for these amplifiers than just nostalgia. I'd heard some exceptionally good-sounding SET-based systems, and that had intrigued me enough to want to check out an SET amplifier should the opportunity present itself.
But for me to seriously consider an SET amplifier, it would have to meet several criteria. The price had to be reasonable in the first place, and tube replacement couldn't cost a fortune. The amplifier had to be able to drive "normal" loudspeakers to satisfactory levels—I wasn't about to start searching for a speaker with +100dB sensitivity just so I could use an amplifier with 2.5W of power. (Most ultra-high-sensitivity speakers I've heard sound hopelessly colored.) I was willing to cut SETs some slack when it came to distortion; as long as distortion is not excessive, the spectrum of the distortion products is probably more important than the amount of distortion. Also, I'd never been convinced that frequency response extending from DC to light was necessarily a good thing.
The Cary CAD-572SE, reviewed by Martin Colloms in the October '98 issue of Stereophile (Vol.21 No.10 p.193), appeared to meet all of these criteria. For a monoblock pair of SET amplifiers from one of the premier names in tube electronics, $2500 is exceedingly reasonable, and replacement output tubes are only $75 each. The rated 20Wpc would not be very impressive for a solid-state amplifier, but it makes the CAD-572SE almost a powerhouse by SET standards. Tube amplifiers tend to overload in graceful fashion, so "tube watts" are often considered subjectively equivalent to double the power from a solid-state design.
I first heard the Cary CAD-572SEs at a neighborhood dealer, American Sound of Richmond Hill, Ontario, where the amps seemed to do a good job of driving a pair of Aerial Acoustics 7Bs—a speaker that is not particularly high in sensitivity. My reference Dunlavy SC-IV's sensitivity clocks in at 91dB, and its impedance is extremely linear, so I thought the combination should work.
Of course, the best way to ascertain equipment compatibility is to actually try it. I borrowed a pair of CAD-572SEs from American Sound for the weekend (Thanks, Angie!), and when the weekend was over, I knew that not only were amplifier and speaker compatible, but that I just had to write about the Cary. To make things more interesting, I requested two pairs of CAD-572SEs, which would allow me to assess the advantages (and possible downside) of driving the bass and the midrange/tweeter sections of each speaker with its own amplifier. Also, Martin's review samples were optimized for a nominal 8 ohm speaker impedance; the samples I received had switches to select 8 or 4 ohms.
Martin Colloms has already provided his usual expert description of the CAD-572SE's design so I won't go over ground that's been thoroughly covered. As someone more comfortable listening to amplifiers than discussing circuit topologies, what I found intriguing about the CAD-572SE is that it's based on a brand new tube. Nostalgia aside, I find it hard to believe that the best of all possible vacuum tubes would be a design that's been around for half a century (pace 300B fans).
The SV572-3 used in the CAD-572SE was introduced in 1996 by Svetlana in Russia, the world's largest tube manufacturer. It was developed from the 811 series of transmitter tubes, and its excellent linearity makes it particularly suitable for use as an audio power tube. The plate dissipation is 125W, which means that it can double as a space heater and provide enough illumination to read Sam Tellig's latest adventures in SET-land by. In Cary Audio's implementation, the SV572-3 is not pushed nearly as much as the specifications allow (and, since it's used in the single-ended mode, it's not pulled at all!), so reliability and longevity should be excellent. The CAD-572SE is not a zero-negative-feedback design, but the amount of loop feedback is very small (2dB), and used mainly to lower the output impedance; the amplifier is said to be stable without any negative feedback.
System & Setup
By the time the CAD-572SEs arrived, the speakers I was listening to were the SC-IV/As, Dunlavy's spectacular follow-up to the SC-IV (see my review in November 1998). A little more sensitivity has been squeezed out of the design (92dB for the SC-IV/A vs 91dB for the SC-IV)—good news for owners of low-powered amplifiers. The rest of the system consisted of a PS Audio Lambda II/Audio Alchemy DTI•Pro 32/Sonic Frontiers Processor 3 digital source, updated Linn LP12/Ittok/AudioQuest AQ7000nsx analog source, Convergent Audio Technology (CAT) SL-1 Signature Mk.III preamp, digital cables by Illuminati (D60/Orchid), and TARA Labs The Two interconnects and Decade speaker cables. The acoustics of my 14' by 16' by 7.5' listening room have been recently improved with the addition of a set of Argent RoomLenses (and removal of the previously used acoustical treatment).
The SC-IV/A has two sets of binding posts, allowing for biwiring or biamping (using the internal passive crossover). I first listened to a single pair of CAD-572SEs with the speakers biwired, then alternated between one and two pairs of amplifiers (ie, passive biamping). The CAT has two sets of outputs, suitable for driving two pairs of amplifiers. However, an additional pair of long interconnects can be a significant expense, so I asked TARA Labs' Matthew Bond if he thought there would be any disadvantage to using a single pair with adapter cables that split the signal near the amplifier end. He suggested that not only was this not a problem, but that there may be a theoretical advantage in having a single rather than a double pair for most of the run (something about the single cable exhibiting less phase shift because of a closer match between the DC resistance and AC impedance). He kindly provided me with cables to explore both options, and, indeed, the single-pair-plus-adapter setup sounded slightly more extended and transparent in the extreme highs than the double pair.
I also compared the amplifiers with the load-matching switches in the 8 ohm and 4 ohm positions. The SC-IV/A's impedance stays mostly between 4 and 6 ohms, dipping to about 3.4 ohms at 60Hz and again at 20Hz, so I expected the 4 ohm setting to be more optimal. As it turned out, the 8 ohm setting produced tighter bass and a generally more open sound. The amplifiers were placed on a PolyCrystal amplifier stand, with PolyCrystal cones under each amplifier. This resulted in significantly improved clarity compared to my previous butcherblock-on-spikes setup.
Use the term "magic" to refer to the sound of an audio system or component and you're likely to incur the disdain of those who view sound reproduction as a mere engineering exercise whose outcome is easily quantifiable through measurement. Yet many audiophiles have had the experience of listening to a system that seems to transcend the electromechanical aspects of sound reproduction, providing almost a direct pathway to the music and the performers. When this happens, it is indeed a kind of magic. Not magic in the supernatural sense, but magic as illusion: a card placed in the middle of the deck somehow appears on top after the deck is shuffled; a sheet of newspaper is torn into small pieces, and—Presto!—it's whole again. You may have a pretty good idea of how the trick is done, but you still find yourself swept up in the illusion. Some systems, and some components, have a high propensity for creating and sustaining the illusion that what you're listening to is not just a reproduction, but plausibly real.
The Cary CAD-572SE is one of these "magic" components. Listening to my system with the CAD-572SE in it, I was repeatedly struck by how utterly lifelike and musically convincing the sound was. I'm not talking about tonal balance that's easy on the ears but homogenizes timbres and lacks detail—each instrument and voice maintained its distinctive timbral character, and there was no shortage of low-level detail, even if this was presented in a subtle rather than a look-at-how-detailed-I-am manner. It was also not just a matter of the sound being "euphonic," except in the sense that recordings were revealed to have a generally more natural, less electronic sound than had previously been the case.
I'd always dismissed the first-generation digital transfer of Frank Sinatra's Come Fly With Me (Capitol CDP 7 48469 2) as sounding pretty rough, and the CAD-572SE did not magically turn it into a 24/96 demonstration piece. Still, when I heard Frank launch into "On the Road to Mandalay" (with the tasteless substitution of "Burma broad" for "Burma girl"), it sounded not so much like a recording than like Sinatra himself, communicating across the years and through the limitations and distortions of all the equipment involved in the recording and playback processes.
This impression of plausible realism (which is, of course, critically dependent on the rest of the system as well) is the CAD-572SE's signal characteristic, and goes a long way toward explaining the allure that SET amplifiers have for many audiophiles. Tonal balance was perhaps very slightly on the sweet side, but the highs didn't sound obviously rolled off or lacking in air. Grain was conspicuous by its absence, with sibilant splash less intrusive than with any other power amp I've had in my system. Soundstage width and depth were superb, and images had a breathtaking three-dimensionality.
Doubling up on amplifiers brought about improvements in the two areas in which SETs are generally acknowledged to be weak: dynamic range and bass extension. Actually, a single pair of CAD-572SEs was able to drive the SC-IV/As to pretty high levels, but with some loss of the sense of ease that characterized performance at lower levels. Bass with a single pair was quite credible on its own, but comparison with the Sonic Frontiers Power 2 or—even more so—a pair of Bryston 7B-STs showed that the SC-IV/As' full potential for bass extension and power was not being realized. The addition of a second pair of amplifiers should theoretically increase the SPL ceiling by 3dB, and this was accomplished handily, but the effect went beyond that. At moderate to high levels—below audible clipping—there was simply a greater sense of authority, of dynamic freedom, and the bass gained in both impact and extension. There was also an enhanced sense of space.
Apart from the additional cost, and assuming that the speakers have the requisite biwire capability, is there a downside to using two pairs of CAD-572SEs? My initial answer to this question would have been a firm "No." Then, as I listened alternately to the two configurations (with some adjustment of the volume control, as volume was not exactly the same on switchover), I gradually came to feel that the sound with a single pair of amplifiers, although with a lower dynamic ceiling and not as even a balance between the top and the bottom, had a little more immediacy, and a finer delineation of low-level detail—a little more of the magic. (Interestingly, in brief demonstrations I gave to three audiophile friends, the two who have high-powered solid-state amplifiers in their own systems much preferred the biamped setup, whereas the third one, a tube guy, liked the single amp more.)
Single-ended triode fans like Sam Tellig are not out to lunch—there is something special going on here, and the CAD-572SE's compatibility with speakers of more or less normal sensitivity makes it a prime candidate for consideration if you're at all curious about what SETs have to offer. At $2500/pair—or even at $5000 for two pairs—the CAD-572SE is a real bargain.
The Cary CAD-572SE is not the universal amplifier. In my room, it was able to drive the Dunlavy SC-IV/As to levels that I found quite satisfactory, but if your preferred listening level is similar to that mandated by THX ("The Audience Is Deafened"), the CAD-572SE would not be my first recommendation. If you want impressive hi-fi, with gut-wrenching bass and brilliant highs, you'll probably find the sound with the CAD-572SE underwhelming. However, if what you're after is music, and you're willing to accept some limitations in low bass and dynamics, this could be exactly the amplifier for you.—Robert Deutsch