Talk to enough people about tubes (or valves, as Europeans call them), and the extreme views you’ll hear will make you think you’re talking politics or religion: Tubes are obsolete technology that should’ve been relegated to the scrap heap decades ago, when transistors came along. Tubes are the holy grail of amplification for the musicality of their sound.
For me, the truth lies somewhere between those extremes. I tend to use high-powered, top-quality, solid-state amplification in my reviewing for its strict neutrality, high detail, and imperviousness to difficult speaker loads. However, I’ll occasionally turn to tubes for pleasure, the simple reason being that some tube amps sound so darn good. That sound is the chief reason I requested a review sample of Copland’s CTA 506 two-channel amplifier from Divergent Technologies, the Danish company’s North American distributor. I also wanted to know what a 21st-century implementation of this ancient (by audio standards) technology sounded like.
Copland released the CTA 506 in 2011. It retails for $6500 USD and is claimed to output 90Wpc into loads of 16, 8, and 4 ohms -- fairly high power output for a tube amp measuring a modest 16.8”W x 7.5”H x 15.2”D. The CTA 506 achieves this output with four KT120 output tubes, which Copland describes as a new variant on the 6550 and KT88 tubes. They claim that the KT120 is the highest-power audio tube currently in production, and that they’re among the first to use it: “The CTA 506 push-pull output stages consist of a pair of matched KT120s in fixed ultra-linear configuration, giving the low distortion of triodes combined with the power of tetrode valves.” The CTA 506 also uses two 6550, four 12BH7, and two ECC81 tubes. Copland says that the user can expect each of these to last about 4000 hours -- quite a long time.
Unlike many tubed amps, which have a “stepped”-looking chassis and case with the tubes displayed in front, as if on a stage, and the large transformers at the rear, the CTA 506 has a conventional rectangular case and weighs 57 pounds. Glance at its 1/4”-thick silver faceplate and you’d easily mistake it for a solid-state amp, particularly if the interior lights that illuminate the tubes aren’t turned on. Besides tubes’ sound, another of their attractions is visual, which is why designers tend to display them in appealing ways. Copland’s not shy about this: “The huge thermionic power valves used in this construction are very attractive to look at; we have therefore decided to make them clearly visible by situating the valves behind lateral perforations on the front panel, thus creating what we consider to be a stunning design to match the sonic virtues of this amplifier.”
Other than those slits, you’ll find on the CTA 506’s faceplate only the power switch. (The CTA 506 shown on Copland’s website at the time of this review had the rocker switch used in the first production run; this has been changed to a rotary control, which is what my review sample had.) On the rear panel are the switch for the interior lights, an IEC power-cord inlet, one pair each of single-ended and balanced inputs, and three pairs of speaker-cable binding posts, for ground, 4 ohms, and 8 ohms. I used the CTA 506 with a pair of PMC’s twenty.24 speakers, whose nominal impedance remains mostly at 8 ohms or above. But I also used it with AudioSolutions’ Rhapsody 80s, which hover between 4 and 8 ohms. I tried both of the Copland’s outputs with the Rhapsody 80s and got better bass solidity and control through the 4-ohm posts.
Overall, I found the CTA 506’s styling and build good for the price, though Copland’s one-year warranty is, I think, way too short. (Copland’s distributor, Divergent Technologies, says they offer two years for the CTA 506 in the North American market.) I can understand a short warranty for the tubes, which wear out and fail, but otherwise, I think any audio component should be warrantied for at least three years.
Because the CTA 506 I received was a demo unit that was well used and already broken in, I could jump right in and start listening. But, like most tubed gear I’ve used, the Copland required a bit of warm-up each time I turned it on before it sounded its best. It began to sound respectable after about 10 minutes, and at the 20-minute mark the sound was smoother, the soundstage larger, and the images on that stage fuller and more dimensional. After 30 minutes, I knew exactly why I still listen to tubes. The sound had the qualities -- that unmistakable tube sound that seems to occupy physical space in a listening room -- that make solid-state amps, no matter their price, seem a little thin and lifeless in comparison.
The most noticeable thing about the CTA 506’s sound was its reproduction of the midrange, which was far more palpable and present than any transistors I’ve heard can muster -- that rich, full, robust sound that gives male and female voices warmth, and instruments texture and life. Mick Jagger’s center-stage vocals in “Fool to Cry,” from the Rolling Stones’ Black and Blue (16-bit/44.1kHz FLAC, Virgin), tangibly hung in space, with dimensionality in all directions and an authentic sense of weight, whereas it always sounds a little less present and palpable through even a topflight solid-state amp. Mariza’s voice in her Transparente (16/44.1, Times Square) was superclean and ultrapure, with a little more heft and body than I’ve heard through traditional solid-state gear. Glenn Gould’s piano in his A State of Wonder: The Complete Goldberg Variations of J.S. Bach 1955 & 1981 (16/44.1, Sony Classical) can sound somewhat threadbare through many solid-state systems I’ve heard, particularly if the speakers are lean through the mids, but it certainly sounded rich, full, and more like a real piano through the CTA 506. The rich, grand sound of Ola Gjeilo’s piano in “North Country II,” from our 2L-TWBAS 2012 Sampler (24/176.4, 2L/SoundStageRecordings.com), is inherent in the recording, so it needed no help from the CTA 506 in that regard. But the CTA 506 did enrich things a little by giving the sound of this recording a touch more fullness, which gave it an even more majestic and authoritative feel, and made the piano sound all the more real.
The CTA 506’s reproduction of soundstages was awesome, even if it didn’t cast the largest stages I’ve heard -- that distinction goes to Simaudio’s Moon Evolution 870A solid-state amp ($20,000, review forthcoming). Still, the CTA 506 sounded commendably open, with musicians’ locations easily identifiable from front to back, not merely pinpointed in space but with presence and palpability that bordered on the holographic. This three-dimensionality let Jagger’s voice stand out more starkly than usual from the somewhat messy mix of “Fool to Cry,” and Gould’s piano stand out more realistically in contrast to the space around him. Ola Gjeilo’s piano, which is close-miked in “North Country II,” seemed a real presence in my listening room, dominating the space between the speakers -- the sound was extremely realistic.
Copland’s claim of 90Wpc power output for the CTA 506 is fairly high for a tube amp, though not for a solid-state design. The Simaudio 870A puts out 300Wpc into 8 ohms -- and costs more than three times as much. Bryston’s 4B SST2, one of my reference amps, is also rated at 300Wpc into 8 ohms, but costs only $5000. Basically, a good-quality solid-state amp will give you more power, and thus more headroom, than most tube amps, even those outfitted with KT120 tubes.
On the other hand, even at loud volume levels the CTA 506 didn’t distort or clip, even in my very large listening room and with speakers of average sensitivity (the PMC twenty.24’s sensitivity is about 85dB/W/m). I think that, in most typical listening environments and short of the most demanding situations, the CTA 506’s power should suffice -- we use only a few watts for most of our listening, so 90W should be plenty for most applications. Plus, there’s another thing about tube amps that most solid-state amps I’ve heard can’t quite match: at lower listening levels, tubes tend to sound more alive, rhythmic, and dynamic. Some have attributed this to “tube watts” being more powerful than “solid-state watts,” which is nonsense -- a watt’s a watt. But I experienced complete pleasure when I listened to the CTA 506 at below-normal listening levels.
Where the Copland suffered in comparison to high-powered solid-state amps was at the frequency extremes. The CTA 506’s bass was full and robust, but not as visceral or impactful as that of the Bryston 4B SST2. The Copland’s highs were sweet, clean, and well extended, but not as airy, effortless, and light as the Simaudio 870A’s. I wasn’t surprised. Tubes have always been more about what happens between the audioband extremes, whereas transistors perform equally well throughout the audioband. On top of that, the Bryston and Simaudio are heavyweight champs in the lows and highs -- they’re better than most solid-state amps in those areas, which means that no tube amp stands a chance of beating them on those grounds. I couldn’t have put the CTA 506 up against tougher competition.
But in comparison to typical tube amps, I think most people would find the CTA 506’s bass quite full, pretty punchy, and more than respectably tight. I think almost everyone would find its highs clean, sufficiently extended, highly detailed, and airy enough. I heard none of the overly warm bass mush or rolled-off highs of yesteryear’s tube designs from the Copland; on the contrary, I found plenty to commend about its sound -- so much that I was left with next to nothing to criticize.
The Copland CTA 506 is a modern-day implementation of tube technology with a thoroughly enjoyable sound that retains the best aspects of tubed designs -- a rich midband and a grand presentation overall, smoothness from the bass through the highs, appreciable soundstage width and depth, tangible soundstage images, and superb image delineation -- while doing an admirable job of avoiding the technology’s weaknesses. Tube fans will find the Copland CTA 506 a solid value.
. . . Doug Schneider
Copland CTA 506 Stereo Amplifier
Price: $6500 USD.
Warranty: Two years parts and labor (only in North America; one year elsewhere).
North American distributor:
Divergent Technologies, Inc.
Phone: (519) 749-1565
Fax: (519) 749-2863