Solid State Power Amp Reviews

My editor felt it was time to survey a handful of what might be called "entry-level" high-end amplifiers. These five amps, offering a glimpse of what high-end sound is all about, range in price from just under $400 to slightly less than $1200. Each, in its way, can serve as a vital link in a system which, with carefully chosen associated equipment, will reward the listener with a highly detailed, focused, emotionally involving musical experience. These amplifiers have proven popular with consumers and have received various degrees of attention in the audio journals. They are reliable, good-looking, and supported by solid, accessible companies. This survey is limited to those amps Stereophile had on hand at the time and which we felt deserved a re-examination. If your favorite amp is not among those reviewed here, don't fret. Lack of inclusion in this survey does not mean other products are without merit. (I understand that the Adcom is to be replaced, but JA thought it still worth including as it represents a benchmark performance due to its success in the marketplace.)

The $750 Adcom GFA-555 was first reviewed in Stereophile over four years ago by Antony H. Cordesman (Vol.8 No.4), who considered it precedent-setting. Shortly thereafter, J. Gordon Holt also gave it a listen (Vol.8 No.7) and came away equally impressed. It has remained a Class C recommended component. Though not constructed to Mark Levinson standards (none of the amps in this survey are), it is nonetheless an attractive, user-friendly piece of gear. It is a direct-coupled, high-power, high-current design with class-A bias for the input stage. A huge, 700VA toroidal transformer is coupled with a total capacitance of 60,000µF. Current capacity is said to be 20A peak-peak. If 200Wpc into 8 ohms isn't enough power, the amp is easily bridgeable (flicking a switch on the back panel) to provide 600W mono into the same load with less than 0.25% THD. With my Acoustats, a pair of Adcoms would give me 850W/side. I would love to hear the effects of such megapower in my system. It could set new standards for quiet!

A single LED indicates when power is on, two other LEDs serving to show when distortion in either channel exceeds 1%. These never lit up during the course of my listening tests. Adcom calls this feature "Instantaneous Distortion Alert." Neat! Heavy-duty 5-way binding posts make speaker hookup easy, even with such outrageously awkward cable as the MIT Music Hose I use. For those who want to rack-mount their equipment, optional extensions are available. These add 2" to the width of the amp. For those who have grown tired of the ubiquitous "industrial black" finish of hi-fi components, Adcom offers their entire line in a glossy white. This should go a long way toward satisfying that important Wife Acceptance Factor, especially as this amp is not a lightweight in either size or appearance.

Turning on the amp caused no surprise thumps or pops, but when I went to switch my preamp (with the phono section selected) from off (standby mode) to straight-wire, a small thunk was heard at the speakers. A minor annoyance perhaps, but not at all like the nasty pop I got from the NAD when it was turned on. I got a similar thunk when I turned off the preamp.

The GFA-555 attenuated record-surface noise to the point that it did not intrude on the listening. Yet I felt the frequency extension in both the bass and treble regions was excellent. Perhaps the amp's speed contributed to this phenomenon. I was impressed with the '555's overall performance. On Poem, the perspective on the soloists was captured just right, with an abundance of hall ambience. Focus was fine, as was the ability of the amp to recover low-level detail. The timbre of the flute had just the right "burnished" metal sound, with excellent balance from top to bottom of its register. The piano was warm-sounding, well-balanced throughout its range, and seemed anchored to the floor. The bass register of the piano had good body, and the treble range rang out appropriately. Though the sound of the Adcom was brighter than either the PS Audio 200C or the Forté Model One, it was not as bright as the NAD or the B&K ST-140.

On The Wellpark Suite, the Adcom exhibited greater depth and wider soundstaging than all the other amps except the Forté. Transients, also, seemed faster. Bass was abundant (even on the Spicas) and well-controlled. Individual instruments on the stage stayed in place, and the sense of the size of the studio was well conveyed. Toward the end of the piece, when the ensemble is going full-tilt, there was never a sense of strain or congestion. Each voice could be heard clearly on the stable soundstage. The timbres of the many different instruments were caught extremely well. The Adcom conveyed the exuberance of the musicians and the excitement of the music on this cut as well as did any of the other amps; better, in fact, than most of them. The James Tyler selection was excellent. This amp presented a well-focused image of the soloist seated in a large hall. The perspective was a little up-front, but this did not detract from the sense of scale of the performance. Low-level detail was excellent, with a barking dog, birds in the rafters, and traffic noises outside the hall rendered clearly. The timbre of the lute sounded natural, with just the right blend of body resonance and string buzz.

On The Trinity Sessions, just after the tape starts rolling and before Margo Timmins starts her solo in "Mining for Gold," the listener should hear the "air" in the church. You do on the GFA-555. Soundstaging is "real" here, with great depth. Better than the PS Audio, about the same as the Forté. Margo's voice sounds a little less husky than on the PS Audio, a bit more angelic. Sibilants were well captured, if a bit accentuated. The vocal doubling was fine, with good separation between male and female voices. Bass extension and body were the same as the PS Audio and Forté. On the Romeros' LP, the Adcom presented a wide soundstage with superb placement of the four guitars. The unique timbre of each guitar was captured extremely well, as was the pattering of the 16 fingertips on the strings. The PS Audio was a little less obvious in retrieving this detail, while the NAD and B&K were slightly excessive on this point. The ambience of the recording site was well captured. On the Tom Waits cut, excellent balance was achieved between the string bass and the piano. The bass was tight, with good extension. You were more aware of the body of the bass with the Adcom than with the PS Audio, NAD, or B&K. The piano overtones were clear and clean, with a very natural decay. An intimate perspective on the two instruments was presented which complemented the music's emotional tone. All in all, I was quite pleased with the Adcom's performance.

Summary and Conclusions
The months I spent with these amps made me much more aware of the kind of sonic signature I can tolerate in a component. What had started out as an exciting assignment turned out, after several weeks of listening, to become tedious and quite fatiguing, both mentally and physically. I found myself getting into a rut. There were times I didn't even want to turn on the system. I was coming dangerously close to audio burnout. But that stage of the review process passed, and I returned to my work with a stronger desire to finish what I had been asked to start. I hope our readers will be among the beneficiaries of my research. I know the local electric company was!

Overall, I was impressed at how fine these amps sounded. Each had its vagaries, some of which I accepted more than others. The Adcom did most things well, other things extremely well. Soundstaging, spectral balance, frequency extension, and accurate rendering of instrumental timbres were superb. It conveyed the dynamic aspects of music in convincing, involving manners. The GFA-555 did not win prizes for its ability to resolve low-level details, but I feel they it be commended for not falling into the trap of pursuing a single desirable sonic feature at the expense of other, more essential ones. The amp let me enjoy the musical experience and forget about the means by which that end was achieved.

I have great respect for the Adcom GFA-555. It's a bargain at its price. It can initiate the listener into high-end sound, has lots of power, looks good, and is a reliable component. It also won in the soundstage category. It worked well with either the Spicas or the Acoustats. For those listeners with a little more money to spend, I highly recommend this product.—Guy Lemcoe