Solid State Power Amp Reviews

Back in May, my vocal ensemble, Cantus, gave a series of concerts in which we covered pop tunes. I'd really enjoyed the sound John Atkinson had gotten on his live Attention Screen CD, so I asked John to come out to Minneapolis and record us. I also thought it might be fun to make John abandon any remaining pretense of "minimally miked" recording and do it up with lots of mikes, like real rockers do. John will be the first to tell you that I'm a bad influence on him.

In order for us to sing with the bass guitar, keyboard, drums, and 20 or so other instruments that would appear in the show, we needed to provide house sound for the singers. I wanted to bring some high-end sensibilities to our audience, so I decided to make the PA out of a real high-end system. My Revel Performa F30 speakers, I thought, would just about crush any Electro-Voice stack out there, or those crappy Bose "professional" speakers I see everywhere—but we needed powerful monoblock amps to drive them. Not owning anything that would fit the bill, I called John and asked if he had any that he could bring. "Oh, I can bring the Musical Fidelity 550k Superchargers, which Michael Fremer reviewed in September 2007. We'll use them just as amps through their line-level input." Gosh, John is helpful.

We hooked up the PA, which consisted of the Superchargers and my Revel F30s, to the other end of John's recording gear, and performed and recorded three nights of shows. It was one of the most natural amplified-concert experiences I've ever heard. As our show included rocking versions of such songs as Pink Martini's "Donde estas, Yolanda?," this system had to play loud. It sure did, but in a way that never drew attention to itself, and with a full-ranged coherence and balance with the other instruments and the venue's acoustics that you rarely hear at amplified shows. The Superchargers never put up a fuss, and after each show were only warm to the touch. I was impressed.

As we packed up after the final concert, I joked to John, "If you want to leave the Superchargers here with me in Minneapolis, I wouldn't mind. Har-har-har."

"Sure," said John. "Why don't you take them and write a Follow-Up to Michael Fremer's review? It could accompany my review of the more powerful 750k Supercharger."

Musical Fidelity's Supercharger concept is that using it between the owner's loudspeakers and current, probably low-powered amplifier will preserve the original amplifier's sound quality even as the Supercharger's enormous power allows the speakers to be driven to much higher levels. I was a good candidate for this—my main amp at home is the diminutive, 30Wpc Pass Labs Aleph 3 (reviewed in April 1997).

First, I listened to the Superchargers alone, operating as standard monoblocks, and fed directly from my Benchmark DAC1 via their single-ended line-level inputs. Just as at the Cantus concerts, I was impressed with the big dynamics and bass control. These things could play LOUD. However, I was also struck with how forward the upper midrange was, how aggressive the treble sounded compared with the Aleph 3, and how flat the soundstage had become. I switched interconnects, messed with AC cables, left the 550Ks playing continuously for a few weeks, and did a few voodoo dances, but was never able to change this fundamental characteristic of these amplifiers. I'm probably more sensitive than most listeners to overly bright systems—I can still regularly hear up to 18.5kHz—but from about 1kHz on up, the Superchargers imparted to the sound a hardness and a harshness that were not subtle.

I then Supercharged my Pass Aleph 3. This was both a step forward and a step back. On the one hand, adding the Aleph returned a bit of neutrality to the midrange, filled out the midbass, softened the aggressive treble, and added a little depth to the soundstage—but this was still not the pure sound of my sweet little Aleph merely writ large. On the other hand, through the amps in tandem, there also seemed to be much less actual information passing through the system. What openness and transparency the Superchargers had on their own now seemed obscured by a slight veil, albeit with a more natural tonal balance.

I returned to my Aleph 3 sans Superchargers. By itself, the Aleph exhibited a neutral, open midrange, a natural extended treble that was free of glare, and a great layering of the soundstage. To be sure, the Aleph's bass control was not even close to what the Superchargers could do, nor did the Aleph give me the feeling that I could keep turning it up forever without it ever clipping. The Aleph played as low as the Musical Fidelitys, but lacked the ability to stop and start my F30s' big ol' woofers with impunity.

For the final showdown, I pitted the little Pass Aleph 3 against the Superchargers and judged both by the standard set by Musical Fidelity: the big dynamic range of a symphony orchestra. I called on the forces of the City of Birmingham (England, not Alabama) Symphony Orchestra and its former music director, Sir Simon Rattle, performing Stravinsky's The Firebird (CD, EMI CDC 7 49178 2), as well as my trusty RadioShack SPL meter, set to C weighting and Fast peaks. The little Aleph was able to create dynamic peaks of around 98dB at my listening chair. The sound was involving and layered, with a very natural orchestral perspective. I could hear the Aleph rounding out the bass-drum thwacks, but I never heard it clip. I could tell that the Aleph wasn't going to play any louder, but it was plenty loud enough for me.

Turning to the Superchargers, I pushed the volume up to peaks of 100dB. Now the leading edges of transients were completely uncompressed, the peaks razor sharp—but so was the sound. Violins sounded steely and brasses as if the sound was coming straight from their mouthpieces instead of their bells.

Musical Fidelity's 550k Supercharger is a neat idea, and I really wanted the pair of them to transcend my system's limitations. But using them either as standalone amplifiers or to Supercharge my own amp, I found their tonal balance too bright and forward of neutral to preserve the magic of the less powerful amp strapped to them, or of the recording itself. The whole point of the Supercharger is to let your system play louder than it would be able to otherwise, but turning them up to the levels suggested by Musical Fidelity made their unforgiving sound only more prominent. While the 550K Superchargers could play loud, in other important musical ways, that was exactly what they couldn't do.—Erick Lichte