Many audiophiles aren’t crazy about Class D power amplifiers. I think it’s more a result of their early education than the innate sonic qualities of the amplifiers themselves. When I was in school if you got a D, you flunked and were considered a dunce. If you got an A, you went to the top of your class. Ask anyone with more than a first grade education whether he’d prefer something that’s Class A or Class D and he’ll immediately say “A.” That’s a hard bias to overcome.
If you explain that amplifier class ratings have nothing to do with sonic quality but merely designate the amps’ efficiency and technology type, many naysayers might give Class A/B, B, C, and even D amplifiers a fairer chance to strut their stuff. In this brave new world of widely fluctuating energy costs (mostly upward) Class D amplifiers have a lot to offer. Unlike Class A amps which squander over 75% of their energy consumption as heat, Class D amps transfer the most of their energy into sound. Efficiency is a good thing.
How much can a Class D amplifier shave off your electricity bill? My own experience indicates that if you leave your power amplifiers on continuously a Class D amplifier will save you at least $400 per year compared with a similarly powered two-channel Class A or A/B power amplifier. That’s $4000 over ten years, which is not an unreasonable lifespan for a top-quality power amplifier. You can buy a lot of music or ancillary gear for $4000.
Although this is a review of two different manufacturers’ monoblock Class D power amplifiers, it’s not a mano-a-mano between them. Instead we’ll look at two Class D amplifier solutions at different prices—a Wyred 4 Sound SX-1000 amplifier costs $1199 while a Bel Canto Ref 1000 Mk II lists for $2995. In the world of Class D power amplifiers, I hope we find that you get what you pay for.
Wyred 4 Sound—Are U Ready?
Despite the semi-literate name, Wyred 4 Sound has an impressive track record. Manufactured and designed by Cullen Circuits of California, which has been responsible for building products for PS Audio, Infinity, BGW, Camelot Technology, and others, the SX-1000 Series II features the latest generation Bang & Olufsen ICE Class D output devices.
While many amplifiers use these output devices, the SX-1000 combines them with its own proprietary direct-coupled, balanced, dual-FET input stage designed by Bascom King. This first stage does not increase gain; instead its primary function is impedance adjustment. According to Wyred 4 Sound, changing the front-end input impedance to 61.9k Ohms “allows source equipment to easily and accurately drive the amplifier.” Stock ICE modules have 8k Ohms on the positive input and 10k Ohms on the negative input, so if you’re using an RCA single-ended input your source would be driving an 8000 Ohm load. Wyred 4 Sound maintains that “the lower impedance your source has to drive, the more you will experience lower volume levels, and slightly higher distortion going into your amplifier. This normally changes the way a preamp can amplify a signal, thus giving you less than optimal sound.”
Wyred 4 Sound also performs modifications to the ICE modules themselves. It bypasses the input coupling caps to allow “audio to freely flow through while still allowing DC protection,” as well as beefs up the servo feedback circuit “for enhanced bottom-end extension.”
The SX-1000 Series II sports both single-ended RCA and balanced XLR inputs. Wyred 4 Sound recommends that users employ the balanced inputs if possible since the amplifier is a true balanced differential design. With a three-conductor balanced XLR signal the “+” and “–” signals are created by the source component, and the ground is simply a shield. With a single-ended RCA connection the amplifier must derive the “–” signal from the “+” signal by inverting it 180 degrees with a phase splitter. According to Wyred 4 Sound’s Director of Sales EJ Sarmento, “We have found that XLR connections have much better sonics than RCAs. The most noticeable effect is that the noise level is reduced. With the SX-1000 Series II some of the cheapest balanced-connection XLR cables can sound much better than some of the expensive single-ended RCAs.” Because of Wyred 4 Sound’s recommendations, most of the time I connected the SX-1000 Series II via its balanced XLR connections.
Wyred 4 Sound populates the SX-1000 Series II with quality parts throughout, including Dale Rn55D copper-leaded resistors, MUSE audio-grade capacitors, a thick-traced PCB board, and WBT speaker binding posts. The amplifier modules are connected to the speaker posts with 14AWG 99.9% OFC high-strand copper paralleled with 14AWG high-strand pure silver wire. Obviously top-tier parts don’t come cheap, which raises the question of why the SX-1000 Series II is so relatively inexpensive. Wyred 4 Sound keeps the price low by using a pedestrian enclosure and by selling directly to end users via its Web site.
Super Sonics 4 The Masses?
I listened to the SX-1000 Series II in all three of my systems. Many reviews of ICE powered amplifiers have mentioned that these amps are more susceptible to frequency-balance variations created by difficult speaker impedance loads. I tried to verify these claims. Most of my listening was done through my main reference speakers, the Dunlavy Signature Vs and Genesis 6.1s. The Genesis presents a more difficult load than the Dunlavys, partly due to its ribbon tweeters and more complicated crossover, but neither is as challenging as some panel designs. On my desktop system I tried more than a half dozen various small two-way transducers. None of the speakers in my arsenal created any noticeable harmonic balance variations. While I wouldn’t completely discount the possibility of speaker mismatch issues with ICE amplifiers, I suspect that harmonic variations may as easily have been the result of input impedance phenomena as speaker impedance mismatches. The SX-1000’s easy-to-drive input impedance makes it less susceptible to timbral balance variations due to input mismatches than earlier ICE designs.
I live in Boulder, Colorado, which is one of the more eco-conscious spots on earth. I’ve been using various incarnations of Class D amplifiers for more than four years and will even admit to a positive bias toward this energy-efficient design. To help maintain my neutrality I keep a Pass X150 Class AB amplifier around as a reference. Even though I’ve spent a lot of time listening to Class D amplifiers, I will be the first to admit that a good Class AB amplifier such as the Pass still sounds more like live music than any Class D amplifier I’ve heard. But most previous generations of ICE-powered amplifiers produced greater differences than the SX-1000 Series II.
The SX-1000 Series II is a powerful amplifier. It excels at producing spookily realistic dynamic contrasts. Even on the most extreme full-scale orchestral material it never fails to replicate lifelike volume levels with ease. The SX-1000 Series II also serves up musical detail with the aplomb of a sommelier uncorking a prize bottle. Subtle musical cues buried deep within complex mixes were as easy to hear through the SX-1000 Series II as through any amplifier I’ve used. Even on my desktop system, which only required the first couple of watts of the SX-1000 Series II’s resources, I was immediately aware of the SX-1000’s dynamic finesse and low-level resolution. The SX-1000’s speed and transparency make for arresting listening.
On a liquid/dry, warm/cool harmonic-balance continuum, the SX-1000 Series II is on the cool/dry side. Its overall balance reminded me of one of the first great Boulder amplifiers, the AE-500, which had a similarly clean matter-of-fact presentation. Compared to the Pass X150, the SX-1000 seems more mechanical and less musical, especially in the lower midrange.
Lateral imaging through the SX-1000 Series II has the precision of a well-rehearsed drill team at a Sunday parade. Front-to-back imaging does suffer from some truncation, however. While I’m not a huge fan of classical recordings that use omnidirectional microphones, I find them very handy to judge an amplifier’s ability to render three-dimensional space accurately. The latest SACD recording from Ray Kimber, Joseph Haydn’s String Quartets in D minor and F major performed by the Fry Street Quartet, is especially useful for this. If a system handles spatial cues correctly, as Kimber’s remarkable demo system at the most recent Rocky Mountain Audio Fest did, it will accurately render the coverage circles for each microphone. In my own system, even the Pass X150 doesn’t get these coverage circles completely right. It renders them more as ovals than circles—they have the correct width, but they are no longer quite as deep as they are wide. The SX-1000 further compresses these circles into shallow ellipses.
In Robert Harley’s review of the NuForce ICE-based Class D amplifiers in Issue 166 he noted a “chalky coloration” to their rendition of upper-mid and high frequencies. At first I didn’t notice any electronic texture through the SX-1000 Series II amplifier. The little electronic grain that was present through the SX-1000 Series II had the consistency of finely ground espresso rather than chalk dust…sorry, I couldn’t resist. But, yes, there is something in the way of electronic grain that doesn’t exist in live music. It is subtle—so subtle that unless you concentrate on it you may not notice it at all.
Filling In the Blanks
The alchemy of putting together an optimal system at any price point comes down to component-matching. Given my predilection for dynamic-driver-based speaker systems it should come as no surprise that I found the SX-1000 Series II amplifier to be an outstanding value with only a few sonic flaws. I suspect if I were more into SET amplifiers, electrostatics, horns, or full-range ribbons I might be less favorably impressed, but then again, perhaps not. The only way to know for sure if the SX-1000 Series II will float your boat is to try it out in your own pond. Since Wyred 4 Sound sells directly to end-users and expects them to give the SX-1000 Series II a thorough shakedown cruise, I encourage you to try it if you are looking for a moderately priced high-power high-efficiency amplifier.
Bel Canto—A Beautiful Voice
Bel Canto has been making high-end electronics for over fifteen years. Its first products were single-end triode tube amplifiers, and although he no longer offers any SETs, John Stronczer, Bel Canto’s principal designer, still uses single-ended tube amps and live music as references for his latest ICE-based switching amplifiers.
Bel Canto was among the first high-end audio manufacturers to embrace switching amplifiers. Its original EVO series was built around the Tripath or Class T amplifier module. But even before Tripath declared bankruptcy Bel Canto had moved on to the Bang & Olufsen ICE amplifier module. John Stronczer told me, “I was concerned for the future of Tripath, and when Bang & Olufsen sent me its latest ICE power module I was impressed. Frankly, I wasn’t happy with its earlier versions, but the latest ones were good enough to consider building an amplifier around. It’s good technology, and a great part to utilize for a power amplifier.”
The latest Ref 1000 Mk II differs from the original in several profound ways. The only parts it shares with the original are the ICE power module, the top cover, and the front panel. Stronczer told me, “Everything else is basically new.” Owners of the original version can upgrade their amplifier to the Mk II for $1000 per chassis, which happens to be the difference between the original Ref 1000’s list of $3990 and the Mk II’s list of $5990 a pair.
When Bel Canto first announced the Ref 1000 Mk II quite a few pairs of the original amplifier appeared on the used marketplace sites I frequent. This is a common occurrence. Audiophiles are so used to seeing the value of a component drop like a rock when a newer version comes out that many savvy owners sell their older units upon the first rumor of a new model without paying a premium for the privilege. But once Ref 1000 owners realized they could upgrade their original version to the latest model, listings for used Ref 1000s vanished.
Bel Canto changed what it considers the key pieces around the ICE power amplifier modules. It started with the input stage. With the new circuitry common-mode rejection was increased and input impedance was raised from 10k Ohms to 100k Ohms per side. This improved both the measured signal-to-noise ratio and distortion at higher frequencies. The input stage consists of only top-shelf components including Caddock resistors, solid electrolytic ultra-low ESR decoupling capacitors, and low-noise regulated power supplies.
The Mk II amplifier also got a new power supply for the ICE modules. Energy storage was doubled and power rectification filters were added in front of the ICE module’s internal power supply to pre-regulate it. This new power supply has lower noise, reduced sensitivity to power line effects, and better power delivery. According to Stronczer the new high-speed rectifiers in the power supply “have a big effect…they changed the sound more than I’d expected. I like to measure what I design, and then I listen to the results. In this case the sonic changes were greater than what I assumed from the measurements.”
The Sound of Round
I’ve been using the first generation of Bel Canto’s Ref 1000 amplifiers for the last several years with a variety of speakers. None of the speakers I’ve used has exhibited any harmonic variations with the Bel Canto compared with more conventional amplifier designs. Most of these speakers have been dynamic driver designs, but some, such as the Final 80, were electrostatic speakers. Even with the electrostatics I didn’t notice any harmonic changes.
During the many years that I’ve employed a triad of Bel Canto Ref 1000 amplifiers (one for each of my front three channels) I’ve never had any issues with inadequate output levels, reliability, or heat build-up, even when the three were stacked directly on top of each other. Since I’m a reviewer, these Bel Canto Ref 1000 amps have been moved, connected, and reconnected far more often than they would be in most regular users’ homes. Even with this extra-heavy-duty use they have never failed to function properly. I think the Ref 1000 II’s will be equally reliable.
Since the Bel Canto Ref 1000 Mk II uses the same output devices as the Wyred 4 Sound SX-1000 amplifier you would expect it to share many of the same sonic attributes. You would be largely correct in this assumption. Just like the Wyred 4 Sound SX-1000 amplifier, the Bel Canto Ref 1000 Mk II can deliver copious amounts of power with ease. Dynamic contrasts, whether micro or macro, are recreated without any truncation or homogenization.
The Ref 1000 Mk II also dredges up even the most subtle low-level details with aplomb. It rivals any amplifier I’ve heard in allowing you to easily listen into a mix so you can focus on whichever part or individual line catches your fancy. Even on a ridiculously dense mix, such as “Doris Dreams” from Orchestra Luna, it’s easy to hear the subtle tonal differences between the two female backing vocalists.
The Ref 1000 Mk II’s precise lateral focus places instruments with exactitude across the front of soundstage. It also does a decent job of recreating depth. The Ref 1000 Mk II actually equals the Pass X150’s dimensional abilities. The Ref 1000 Mk II does a noticeably better job of recreating omnidirectional microphone pick-up patterns than the Wyred 4 Sound SX-1000 amplifier. Although the pick-up patterns on omni microphone recordings are still not perfectly round through the Ref 1000 Mk II, the Bel Canto does make them a less extreme oval than the Wyred 4 Sound’s shallow ellipse.
Harmonically the Bel Canto Ref 1000 Mk II has a slightly warmer, more musical presentation then the Wyred 4 Sound SX 1000. The Bel Canto closely approaches the warmth and musicality of the Pass X150, with only a smidgen less richness in the upper bass and lower midrange. The Bel Canto is also less mechanical sounding than the Wyred 4 Sound, and while the Bel Canto may not warm up an overly sterile-sounding front end or speaker like a classic tube amplifier, it certainly won’t further subtract from the harmonic warmth of a system.
What makes the Bel Canto Ref 1000 Mk II worth more than twice as much as the Wyred 4 Sound SX-1000? It’s certainly not twice as good, but it does excel at recreating the musical event in a more natural, organic, and convincing way than the SX-1000. Harmonic differences between these two amplifiers were more obvious through the Genesis 6.1 speaker system than through any of the smaller two-way monitors I’ve reviewed recently. The Bel Canto’s midrange was more realistic with a greater sense of immediacy and presence. Also the upper treble had less electronic grain with the Bel Canto amplifier.
Obviously the speaker used to compare any two amplifiers has a major influence on the perceived differences between them. Through the Dunlavy Signature VI speakers I was more aware of the depth variations between the two amps than their harmonic differences. On “Oh Dry the Glistening Tear” from the Charles Mackerras version of Gilbert and Sullivan’s Pirates of Penzance, the Bel Canto Ref 1000 Mk II allowed each voice in the female chorus to retain its individuality and location in space while still blending into a three-dimensional chorale. With the Wyred 4 Sound SX-1000 the choristers were far more spatially compressed and less three-dimensional. Also the separation between the back line of choristers and the back of the stage wasn’t as well defined through the Wyred 4 Sound as it was with the Bel Canto.
Class D or Class A?
Some audiophiles will never be swayed from their Class A solid-state or single-ended-triode amplifiers toward Class D designs. Just like the owners of gas-guzzling Lamborghini or Maserati sport coupes, the goal of “ultimate performance” trumps any concessions to efficiency or green consciousness. But audiophiles with a more expansive worldview may find the idea of saving substantial quantities of energy and money by using a Class D amplifier more acceptable. If you like the concept of an amplifier that is compact, efficient, powerful, transparent, musical, and extremely reliable, the Bel Canto Ref 1000 Mk II amplifier could be the last amplifier you’ll ever want or need. Hey, it’s worked for me.
SPECS & PRICING
Bel Canto REF1000 MKII monoblocks
Power output: >1000W into 4 ohms, >500W into 8 ohms
Frequency response: 20Hz-20KHz +/-0.5dB
Damping factor: >1000
Dimensions: 8.5" x 3" x 12"
Weight: 15 lbs.
Price: $2995 each
Bel Canto Design, Ltd.
221 North 1st Street
Minneapolis, MN 55401
Wyred 4 Sound SX-1000