During the time that I’ve been a reviewer for The Absolute Sound I’ve played host to many power amps. Some were large, heavy, and sucked juice from my AC outlets like a dehydrated Great Dane, while others were so small that they could even fit into one of those “tiny houses” featured on HGTV. But whether big or small, powerful or flea-watt, all power amplifiers perform the same function: supplying somewhere between 20 and 30dB of gain, turning a volt or two into multiple watts of power. But even after all these years there is still no way to know, before listening, how well a particular power amplifier will mate with a given set of loudspeakers. Often the subtle differences between a synergistic match and one that leaves something to be desired comes down to things that we can’t measure reliably in a home listening room by any methodology except listening.
Obviously after many years of listening to and using power amplifiers I have developed my own set of preferences. I am not a big fan of big, heavy, energy-sucking, high-power, and usually expensive-to-own power amplifiers. And while low-power single-ended tube amplifiers can sound superb when connected to the “right” loudspeaker, they certainly aren’t a universal power-amp solution. In recent years, I have gravitated towards high-efficiency power amplifiers that use switching technology. The first units that sounded good used a Tri-path module; later, B&O ICEpower modules came along. Recently, some manufacturers, including Bel Canto, have been using Hypex modules as the heart of their Class D designs. Wyred 4 Sound’s new power amplifier, the SX-1000R, uses the B&O ICE power module. Does this current incarnation of Class D topology finally deliver all the sonic special sauce found in traditional solid-state AB or even Class A designs? Let’s find out.
The SX-1000R monoblock power amplifier can produce up to 625W into 8 ohms with 1% THD and noise, and 1225W into 4 ohms at the same distortion level. It delivers 27dB of gain with 118dB of dynamic range. The SX-1000R has an output impedance of only 0.005 ohms and a damping factor of 2000 at 100Hz into 8 ohms. Although quite powerful, the SX-1000R draws only 15 watts at idle and has an efficiency of 78% when delivering 500 watts into 8 ohms. Compare this to a Class A amplifier, which averages only 25% efficiency, and you begin to see how much more energy-efficient the SX-1000R is compared to older power amplifier topologies.
Although the SX-1000R has at its heart the B&O ICE module, much of the rest of its design is proprietary, such as the field effect transistor (FET) input buffer that supplies both single-ended and balanced input options. This circuit includes a dual-differential common mode converter, originally developed for the Wyred 4 Sound DAC-2, that produces a true balanced signal. The SX-1000R’s front-end design also isolates the power amplifier from impedance mismatches: Its high 91k ohm input impedance matches both solid-state and tube preamplifiers without loading down their output stages. Wyred 4 Sound’s third-generation circuit topology also significantly reduces the detrimental effects os noisy sources due to its balanced circuitry, audio-grade capacitors, and quad-paralleled front-end layout.
The SX-1000R replaces the now-discontinued SX-1000 that garnered TAS’ Editors’ Choice award for six years in a row. Since the new amplifier uses many of the same parts, including the chassis, Wyred4Sound offers a trade-in program giving owners of the earlier-gen amp the option of upgrading to the new design for $2000 (for amps up to three years old). If your SX-1000 is more than three years old the trade-in will cost an extra $200, or $2200 plus your two amps. Unlike many firms that offer only a one- or two-year warranty, Wyred 4 Sound offers a five-year warranty on the SX-1000R.
Cosmetics, Ergonomics, and Setup
The SX-1000R power amplifiers will never qualify as audio jewelry, but I think their understated looks are in line with Wyred 4 Sound’s focus on performance rather than bling. The SX-1000R is available with either a black or slate-gray chassis. The front panel features a thin blue line of illumination of adjustable intensity flanked by a pair of wedge-shaped, satin-black corner panels. The SX-1000R’s on/off switch is located on the back along with one pair of five-way binding posts, single-ended RCA and balanced XLR inputs, a 12-volt trigger, and an IEC AC input. Both sides of the its chassis sport a row of diagonal ventilation slots. One minor quibble with the SX-1000R’s layout: There’s no on/off switch on the front panel, so when or if you want to turn the amp off, you will need to access its rear panel.
Installing the SX-1000R monoblocks in my two primary listening systems was easy. They are relatively small at 8.5 inches wide, 4.125 inches high, and 13.5 inches deep—and certainly light at only 13 pounds each. In both setups I used the balanced XLR input connections. The banana terminations on the Audience Au24 SE speaker cables fit snugly into the SX-1000R’s WBT five-way binding posts. When connected and powered on there is no physical noise from the SX-1000R. Even when I placed my ear directly on its cabinet I could hear nothing—no hum whatsoever. This quiet extended to the loudspeaker output when the input was muted—with the 94dB-sensitive Spatial Audio M3 Turbo S speakers I needed to be within four inches of the tweeter to hear any hiss.
My primary listening room is very quiet, with a steady-state background-noise level of 35dB. So, the noise, or lack of noise, of the power amplifier is very important to me. The SX-1000R proved to be almost as quiet in base noise level as the Bel Canto REF600M monoblock amplifiers I reviewed recently, and quieter than the Pass Labs X150.8 stereo power amplifier. Having an amplifier that doesn’t add to the noise floor is very important, not only for low-level information retrieval, but also so the speakers disappear completely from aural view. Obviously, audiophiles with less sensitive (say 90dB or less) loudspeakers will find the SX-1000R to be even quieter than I did.
One of the most dominant sonic characteristics of the SX-1000R is its sense of unlimited power. With both the Spatial Audio M3 Turbo S and Audience 1+1 loudspeakers there was never any sense of strain or added hardness during even the most punishing triple-fortissimo passages. Also, the SX-1000R’s control of the drivers, due in part to its high damping factor, meant the chances of the Audience 1+1’s transducers getting damaged during momentary high SPLs was reduced to the point where I didn’t worry about it after the first couple of days of use.
And what does the SX-1000R sound like? It sounds like whatever music you choose to play through it. This is not an amp for someone who is trying to warm up, sweeten, or euphonize his system. No, the SX-1000R is very much a “straight, no chaser” sort of device where the harmonic balance doesn’t get “improved” and that badly-recorded cymbal will still sound like eggs frying (as it should). But on well-recorded albums, such as Todd Rundgren’s Runt, which is over 30 years old, it was easy to hear that the newly remastered MQA version on Tidal had a level of clarity and articulation that I had never heard from previous releases. I was even more aware that the piano was recorded on a tape machine that had some speed stability issues, but the increased lucidity of the presentation made even that sonic wart more acceptable.