Steven Stone is the former editor of AudiophileReview.com. He a longtime audiophile and home theater writer, as well as a musician and recording engineer. Steven has written for publications like Stereophile, as well as HomeTheaterReview.com, AudiophileReview.com, and The Absolute Sound.
Steven is plays guitar, mandolin, and Ashbory bass and is a collector of fine musical instruments.
Power amplifiers are a necessary evil. The necessary part is obvious: without power amplifiers, speakers would be mute. The evil part comes from their weight, power inefficiency, and occasionally ungainly size and looks. Yes, there's a good reason why most power amplifiers spend their working lives ensconced in equipment racks.
Power amplifiers don't have to be hulking behemoths, though. One way to make power amplifiers smaller is to create a mono-block power amplifier that handles only one channel. Another way is to use the latest Bang and Olufsen digital ICEpower amplifier module, which B&O claims is more efficient than conventional power amplifier circuits. Wyred 4 Sound has employed both of these methods to create an eight-pound, single-channel power amplifier capable of producing 430 watts into four ohms that measures only eight inches square by 3.5 inches high. Although not quite juggle-able by your average audiophile, the $899 Wyred 4 Sound mAMP still qualifies as a very small-footprint amplifier capable of big sound.
Although the B&O ICEpower circuit serves as the heart of the mAMP, Wyred 4 Sound hasn't merely stuck a circuit board into a case. Wyred 4 Sound begins with the latest module from B&O and mates it with Wyred 4 Sound's "completely redesigned" input stage. This input circuit accepts both single-ended and balanced XLR inputs and includes a dual-differential common mode converter so that the mAMP can operate in pure balanced mode, whether the input signal is balanced or not. The input circuit also isolates the front end to eliminate input impedance mismatches between the mAMP and whatever is connected to it. The mAMP's input buffer has 100k impedance, which should make it "play nice" with virtually any preamp, tube or solid-state.
Wyred 4 Sound refers to the mAMP as "third-generation technology" that significantly reduces operating noise by using balanced circuitry, low-noise capacitors, and a quad-paralleled field effect transistor buffer. With a published specification of less than 125 uV and a 111dB dynamic range, the mAMP also offers slightly more gain than the standard 26 dB with 30.5 dB. For most systems, the extra 4.5 dB will be a welcome addition but, if you have any ground-loop hum issues or an especially noisy CD player or preamp, the mAMP will also make the noise slightly louder than would a conventional gain amplifier.
Installing the Wyred 4 Sound mAMP is no different than installing any other power amplifier. You have a choice of balanced XLR or single-ended RCA line-level input connections and a set of gold-plated five-way speaker binding posts for speaker connections. The rear of the mAMP also has a pair of 12-volt trigger connections, an IEC AC connection, an on/off switch, and a sliding universal voltage adjustment switch. For most of the review, I used the pair of mAMPs in my computer desktop system, where they mated successfully with a number of speakers, including the 89dB-efficient Golden Ear Aeon 2 and the 84dB-efficient Audience ClairAudient "The One" speakers. I also used Role Audio Canoes, ATC SCM7s, Silverline Minuet Supremes, and Ariel Acoustic 5Bs. Near the end of the review period, I installed the mAMPs in my two room systems, where they drove my Dunlavy Signature VIs, Genesis 6.1s and Skiing Ninja-modified AV123 X-Static speakers. I also used a variety of speaker cables, interconnects, and digital cables from Synergistic Research, AudioQuest, Kimber, Wireworld, and Transparent Audio.
Wyred 4 Sound touts the mAMP's energy efficiency. Its idle power consumption is only 9.5 watts and standby consumption less than 0.5 watts. However, the amplifier doesn't run as cool as the specifications suggest. After being in operation for more than 30 minutes, the mAMP produces more heat than some "high-efficiency" amplifiers. While never too hot to touch, the mAMP does get more than merely warm and should be installed so that it has some some air circulation around it.
Although the mAMP is small in overall size, the cabinet itself is quite robust. Machined from a solid piece of 0.75-inch-thick aluminum, the front panel has a "line-grained" texture with black anodizing. The mAMP's chassis is made of black powder-coated steel with top and side venting for heat dissipation. Although it only weighs eight pounds, if you drop an mAMP on your foot, you will not be a happy camper.
Read about the performance of the Wyred 4 Sound mAMP on Page 2.
The mAMP may be small in size, but it produces a lot of power. It nearly doubles from 255 watts at eight ohms with 0.2 percent harmonic distortion to 430 watts at four ohms, and it can successfully drive loads down to three ohms. How powerful is 430 watts into four ohms? In a case of gross user error, I fried the drivers in my pair of Audience ClairAudient "The One" speakers when I accidentally had the volume level on a Lynx Hilo DAC/PRE turned up to 100 (out of 100). It only took a nanosecond of ABBA's Greatest Hits to propel both drivers so far out of their gaps that they left indentations on the speaker cones. My advice is, don't try this at home.
Obviously, the mAMP has lots of power, but what about finesse? The most difficult-to-drive speaker I use is the Genesis 6.1. The mAMP mono blocks had no trouble driving them to satisfying volume levels, without any signs of stress. I was also impressed by the mAMPs' ability to render subtle details within the mix. I regularly record the Boulder Philharmonic Orchestra's concerts. The most recent performance featured the world premiere of a symphony by Jeffry Nytch, commissioned by Exxon/Mobil and the Geological Society of America. In keeping with the geologic theme of the piece, the percussion section uses gold panning tins filled with rocks as one of the "instruments" in the piece. The mAMP made it easy to differentiate these new percussion devices from more traditional instruments.
With more conventional music, such as The Definitive Doc Watson, regardless of which system I used, the mAMP mono blocks had enough resolution and inner detail so the differences between the different vintages of recordings (the album includes recordings made as early as 1961 and as late as 2006) were immediately obvious. Some, such as "Omie Wise," which was recorded "sometime between 1970 and 1976" according to the album notes, have Doc's vocals panned all the way to the right side of the soundstage. The mAMP did an excellent job of keeping Doc's voice in place with a well-defined and rock-solid image.
One of the aural qualities I admire most about the Audience ClairAudient "The One" single-driver full-range speaker is its imaging abilities. With the mAMP driving them, these speakers virtually disappeared, leaving only an easy-to-listen-to, well-defined and precisely rendered soundstage. I'm in the process of transferring some of the LPs in my collection that have never been made into CDs. One of these LPs is the classic Bill Monroe album Bill Monroe Master of Bluegrass (MCA 5214). On one cut, "Lady of the Blue Ridge," Bill laid down four separate mandolin tracks. Listening through the mAMP/Audience combo, each mandolin part retained its individuality, instead of merging into a homogenous wall of sound.
Some of the rare records I've been transferring to digital aren't pristine and have some surface noise (as do most LPs). Comparing the 44.1/16 transfers with higher-resolution 192/24 versions of the same transfer, the 192/24 files did a much better job of separating the surface noise from the music. The mAMP had the necessary resolution and phase coherence to keep the out-of-phase noise and ticks and pops on a completely different physical plane - in front, like a curtain - while the music played, unfazed, behind the plane of noise.
Some audiophiles demand tubes somewhere in their audio system. The mAMP doesn't have any tubes so, if you must have a tube-based power amplifier, the mAMP won't fill the bill. The mAMP is a superbly neutral power amplifier that won't add any euphonic tube warmth to your system.
Since it has slightly more gain than a conventional power amplifier - 30.5 dB vs. the more standard 26 dB - the mAMP can have a greater sensitivity to hum and noise. When I first put it into my computer audio system, I noticed some extremely low-level hum that had not been present with the prior amplifier. After spending several minutes re-routing cables, especially AC cables, the hum went away. If you experience low-level hum with the mAMP, chances are that the culprit is not the Wyred 4 Sound amplifier, but rather something else in your system that's not quite right.
Comparison and Competition
After more than a month in my desktop system, I moved the mAMPs to one of my room-based systems. In my large room, a Pass X-150.3 three-channel amplifier, originally priced at $4,500, drives my Dunlavy SC VI mains and SC IV center speaker. When I installed the mAMP mono blocks, I left the Pass X-150.3 on the center channel and powered the SC VIs with the mAMP. I was surprised how closely the mAMP's harmonic balance and dynamic capabilities compared with the Pass amplifier. I felt the Pass amp was a trifle warmer in the lower midrange and upper bass but, depending on the music, my preference for one amplifier's harmonic character over the other changed. Both were equally transparent and so close to what I would consider neutral that changes to software, cables, or upstream sources were all immediately obvious through either amplifier. Both amplifiers also had superb image specificity and rock-solid imaging. Even with my own live concert recordings, some of which have a range of more than 50 dB from loudest to softest, the mAMP rendered dynamics with the same level of bravado as the Pass amplifier.
When I put the two mAMPs into my smaller room system, which usually has three Krell S-150m power amplifiers, $2,500 each, driving either Genesis 6.1 or Skiing Ninja-modified AV123 X-Static speakers, I again found more similarities than differences between the amplifiers. Both amplifiers had very similar harmonic balances, to the point that during several listening sessions I had to look to see which amplifiers I was hearing. On paper, the mAMP appears to have more power than the Krell but, during listening sessions, neither amp displayed any audible signs of stress driving either speaker system.
Yes, we need power amplifiers, but the Wyred 4 Sound mAMP makes a very good argument that a strong power amplifier doesn't have be the size of a small refrigerator to be a top performer. For under $1,800 per pair, you get two very well-made and excellent-performing power amplifiers that won't drive up your energy bill or require a special room or heavy-duty rack to hold them. Well-suited for either desktop or room systems, the Wyred 4 Sound mAMP should be auditioned by anyone considering a power amplifier in the $1,000-per-channel (and up) category.