Solid State Power Amp Reviews

The AMS100
The AMS100 is basically a scaled-up version of Musical Fidelity's 50Wpc AMS50, a sweet-sounding amplifier that I used to drive Sonus Faber speakers at a "Loudness Wars" demonstration I did at Denver store Listen-Up in May 2010. Like the AMS50, the AMS100 is a bridged design with both hot and cold speaker terminals for each channel each driven by a complete mono amplifier. But whereas the AMS50 has a single power transformer and a single bank of eight pairs of electrolytic capacitors to supply the positive and negative voltage rails for both the hot and cold amplifiers, the AMS100 has a separate transformer and a bank of 16 supply capacitors for each channel's amplifier. (A quarter of these capacitors can be seen under the wire-mesh grilles set into the amplifier's top plate.) In addition, these two capacitor banks are each fed rectified DC via a hefty dual bifilar-wound choke that should both filter and cancel ripple on the two voltage rails. Musical Fidelity claims that these chokes reduce ripple on the DC rails by a factor of 88— ie, a very useful 39dB!

The AMS100's power supply thus has four transformers, four chokes, and 64 smoothing caps, which accounts for the amplifier's bulk. The 20 pairs of output devices for the four individual amplifiers are mounted on black-finned heatsinks that run the full height and depth of the chassis. The front panel has a central black section on which pairs of tiny LEDs indicate standby (red), operation (blue), and thermal overload (no idea what color; they never lit up); these LEDs flank a circular, dashpot-style On/Standby pushbutton.

The rear panel sports two pairs of WBT binding posts for each channel to the sides, and, above the central master AC switch and 15A IEC AC inlet, pairs of RCA and XLR jacks for unbalanced and balanced drive. There is also a 12V DC trigger jack and a toggle switch to select balanced or unbalanced inputs.

Listening
The Musical Fidelity AMS100 is a massive beast. It sat between the speakers, and the only concession I could make to practicality was to rotate the amplifier onto its side, then back down onto a small, wheeled, carpet-covered dolly—easier to say than do—so that I could move it around as needed and, more important, raise the amplifier off the carpet to give its heatsinks room to breathe. (The dolly was big enough to support only the AMS100's front and middle pairs of feet; I doubt the lack of support for the rearmost two feet affected the sound quality.)

I drove the AMS100 with balanced signals, and used it to listen to all of the speakers that have passed through my hands for measurement the past few months, and that needed to be listened to by a second set of ears. But to audition the AMS100 itself, I used the Harbeth P3ESR and Rogers LS3/5a minimonitors, as well as the Vivid B-1s, which John Marks raved about in the February 2011 "The Fifth Element."

It seemed an unlikely match, but my 30-year-old LS3/5as sang with the AMS100. The speakers seemed to disappear, transforming their end of my room into a clean, rectangular window on the recorded acoustic with every recording I played, and giving no clues that the music was being generated by a tiny pair of speakers (provided I kept a careful ear on the playback level). And the details of those acoustic spaces were laid delightfully clear. During the review period I mastered jazz group Attention Screen's new live CD, Takes Flight at Yamaha (Stereophile STPH021-2). As I described in the May issue, in the article on the making of this recording, I decided to use a touch of artificial reverberation to "glue" the mix together. The resolving power of the LS3/5as driven by the AMS100 allowed me to quickly zero in on the optimal setting of the Metric Halo reverb engine I was using. (Following the release of the CD, I married a 48kHz downconversion of the 24/88.2k master file for one improvisation, "13 Trojans of Vundo," to the video that was shot at the concert: Check it out.)

The AMS100's resolution of fine detail was especially noticeable with Burt Bacharach's main theme for Casino Royale (24/96 ALAC file, ripped from Columbia/Classic Records HDAD 2007). Other than Herb Alpert's double-tracked flugelhorn in the center of the stage (footnote 1), this 1967 recording is dual-mono rather than stereo, with twin tunnels of sound in the left and right speakers, yet readily audible were such details as the studio acoustic around the mono drum kit in the left channel, and the quiet rolling on a xylophone in the right. With the even-more-resolving Vivid B-1 speakers, the reverb that occasionally envelops the chimes and guitar in the title track of Cornelius's Sensuous (CD, Everloving EVE016) pushed the soundstage far behind the front wall of my listening room and across the street behind it. And the sampled drums in track 2, "Fit Song," demonstrated that the AMS100's 100W speed limit was no impediment to its achieving frightening impact with the Vivid speakers (the LS3/5as and Harbeths, of course, not so much).

There was a seductive sweetness to the Musical Fidelity's midrange. I've mentioned before that I use, as a reference for midrange purity, a 1998 recital by the late mezzo-soprano Lorraine Hunt Lieberson accompanied by pianist Roger Vignoles (CD, Wigmore Hall Live 0013). This recording places Hunt Lieberson well in front of the piano without obscuring the instrument, and the third of Mahler's five Rückert Lieder, "Liebst du um Schönheit," with its appoggiatura-laden vocal line, sent shivers down my back when reproduced by the little Harbeth P3ESRs driven by the AMS100.

This sweetness meant that the Musical Fidelity could cope with poor recordings. I've been listening a lot this past spring to the Buffalo Springfield's 2010 Bridge School Benefit Reunion concert, which I downloaded a while back (no longer available, I fear). The sound of the downloads is bootleg-poor. But with the Harbeths powered by the AMS100, all that could be forgiven and forgotten. Stephen Stills has no voice left, but he still managed to make "Bluebird" ascend to the heavens; Neil Young rocked it to the rafters on "Mr. Soul"; and Richie Furay's "Kind Woman" reminded me that he was always the best singer of the group. This is what great hi-fi does: It allows you to bypass the foibles and failings, so that the music is channeled directly to your soul.

Comparisons
During the time I had the Musical Fidelity AMS100 in house, I also had available the 600W Classé CT-M600 monoblocks, which I reviewed in the March 2011 Stereophile ($13,000/pair); and the 440W MBL Reference 9007 monoblocks, which Michael Fremer reviewed in September 2006 ($42,800/pair). Yes, these are significantly more powerful amplifiers than the Musical Fidelity, but each pair of monoblocks is physically less than half the AMS100's size, and they do bracket its price ($19,999) in logarithmic fashion.

When he reviewed the MBL 9007, MF found it to be "a somewhat cool customer," less "ripe" than some other amplifiers he's heard. "While never bright, hard, or brittle," he wrote, "the overall presentation was nevertheless oriented more toward rhythmic drive, transient speed, and clarity than toward harmonic richness or textural suppleness." This was very much how the MBLs sounded in my system, though the combination of the 9007s and the Vivid B-1s was too much of a good thing. The MBL was a little more forward in the low treble than the AMS100, and as a result less forgiving of the B-1s' balance with overbright recordings. The amplifiers offered similar senses of musical flow, but the AMS100 was definitely sweeter in the highs than the German amplifier. In direct comparisons, however, the AMS100's bass was a bit too warm, and as much as I appreciated the MF's dynamics, the MBL offered more ultimate slam.

The Classé CT-M600s have been my amplifiers of choice for the past year, getting what I felt was the best from every speaker with which I used them. When I listened to "Autumn Leaves," from Cannonball Adderley's Somethin' Else (24/96 ALAC file, ripped from Blue Note/Classic DAD 1020), the Classés offered better upper-bass definition of the double bass, and very slightly more upper-frequency energy with Miles Davis's trumpet and Adderley's alto sax, but the amplifiers were otherwise very close. The Musical Fidelity sounded slightly sweeter in the treble, however, more forgiving than the MBLs or Classés.

I then listened to the CD-definition master of my forthcoming release of pianist Robert Silverman performing Robert Schumann's Symphonic Études. The left-hand register of Robert's Steinway sounded very slightly more veiled with the Musical Fidelity driving the Vivid speakers compared with the Classé CT-M600s, but actually not quite as rich as with the MBL 9007s—something I had not anticipated. But the MBLs again excelled in clarity of line in the treble. The Classés are still my go-to amplifiers for overall neutrality, but there was something very seductive about the Musical Fidelity's sound that I shall miss, now that the advent of summer mandates their return to the distributor.

Summing Up
Musical Fidelity's AMS100 is magnificent. It is also silly. It is the best-sounding amplifier I have heard from the British company: while it doesn't have the sheer slam of their Titan, which I hear regularly in Mikey Fremer's system, its highs have a sweetness that escapes the Titan. It costs a hair short of $20,000 and it weighs as much as I do, but it is restricted to 100Wpc into 8 ohms. (Its shipping crate weighs more than almost all 100Wpc amplifiers.) It consumes electricity as if "Peak Oil" were merely a liberal myth—even in standby, its power consumption exceeds the 1W EEC regulation—and it runs so hot that I had to plan my late-spring listening sessions with an eye on the weather forecast. As I said, silly. But magnificent.

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Footnote 1: Before people write in to tell me that HA was playing a trumpet on this track, I feel his tone is too round, too bugle-like to be a trumpet. But I could be wrong.