Adcom GFP-565 preamplifier Followup October 1990
When he reviewed Adcom's $800 GFP-565 solid-state preamplifier, the GFP-565, in Stereophile's February 1990 issue, Gary Galo enthused at length over its sound quality. Following comparisons with the Forté 2, Adcom GFP-555 and GTP-400, Hafler DH-110, and even the Audio Research SP11 Mk.II, he concluded that the GFP-565 "is a superb preamplifier that can hold its own with all but the most expensive products"; it "sets the standards for preamps under $1000" and easily deserves a Class B rating in Stereophile's "Recommended Components" listing.
However, when I compiled the April 1990 "Recommended Components," I thought it only fair to give the GFP-565 a provisional Class C recommendation and arrange for the preamplifier to be subjected to some further listening in Santa Fe. Accordingly, Gary sent me his review sample of the GFP-565; Victor Campos of Adcom also sent a separate sample.
The GFP-565 has three sets of outputs: Main (Normal and Lab) and Bypass. Although the tone controls can be switched out of circuit when the preamp is used from its Main outputs, the Bypass outputs omit all the tone control and feature switching and are recommended for the best sound quality. I indicate in the text, therefore, where I think there are significant differences between the two sets of outputs.
I used the Galo GFP-565 for a period of two weeks and, to say the least, was impressed. Its line-stage sound, via the Bypass outputs, was robust, with a good delineation of recorded detail. Stereo imaging was well-focused, the perspectives on my own recordings being reproduced with good depth delineation, though in absolute terms, the soundstage was somewhat foreshortened. This wasn't to a great degree, howeverit was significantly worse via the Main outputsand bearing in mind the Adcom's very competitive price, represents respectable performance indeed. On the downside, the extreme treble was a little shut-in, lacking air, even though the mid-treble was, if anything, rather forward. The overall balance was therefore somewhat dark-sounding, with the subjective result that the music sounded rather over-polite, particularly via the '565's Main outputs, when it reminded me of the original version of the less-expensive GFP-555. Low frequencies were also rather ill-defined via the unit's Main outputs, and consistently tubby-sounding when compared with the '565's Bypass outputs.
I couldn't be particularly rigorous auditioning the unit's MM-only phono stage as I didn't want to change my regular LP-playing setup or introduce another variable by using a separate step-up transformer. Nevertheless, as the Adcom's phono input is incredibly quiet, there was only a very slight noise penalty and a restriction on maximum loudness with the Troika taken straight in. And the '565's phono input definitely sounded excellent with the output taken from the Bypass sockets. LP sound was clean, clear, and open, and lacking high-frequency grain. The piano sound on Käbi Laretei's superb Ingmar Bergman film-music piano recital (Proprius PROP 7829) was as natural-sounding as I can remember having heard. Dynamics, too, were impressive via the phono input. The drum sound on John Hiatt's Stolen Moments album (A&M 75021 5310 1) was transient-rich, yet with the individual drum images set back in the soundstage, not unnaturally thrust forward. Check out "Child of the Wild Blue Yonder" for the manner in which the bass guitar is presented with excellent weight yet doesn't become confused with the bass-drum sound. This is definitely phono-stage performance to place this inexpensive preamplifier firmly in Class B of Stereophile's "Recommended Components."
For the first set of comparisons, I connected the Meridian 208's fixed-level outputs into the Mod Squad Line Drive Deluxe with one pair of AudioQuest Lapis, this connected to the Audio Research Classic 60 via 10' lengths of Audio Research interconnect. The AudioQuest interconnects could also be connected to the Adcom's CD inputs, its outputs connected to the Line Drive and its volume control set to unity gain. With the CD player feeding the passive control center unit directly, the sound from this system was stunning. The soundstage was wide and extraordinarily deep.
Robert Harley's guitar and double-bass recording on the Stereophile Test CD has a fragile recorded ambience, yet the best systems throw a dome of subtle reverberation around the two acoustic instruments, both of which should be presented as lying in the same plane, slightly behind the loudspeakers. (Being present for the recording sessions gives an insight into the correct presentation of the recorded soundstage that's hard to beat.) Such was the case with the Mod Squad unit, neither instrument being thrust forward and the chapel acoustic being apparent without exaggeration or loss. The main failing of this system was a slight reticence to low frequencies that manifested itself as a lack of weight to the double-bass sound.
Via the GFP-565's line stage and the Main outputs, the perspective on the instruments became a little distorted, the guitar moving forward of the bass. The surrounding chapel acoustic was also suppressed, not to a serious degree but still noticeable in comparison with the direct feed. The Adcom's low frequencies via its Main outputs were fuller, weightier than via the passive unit, but bass definition was a little compromised, the already soft attacks of the double bassplayer Dan Kolton was stroking rather plucking the stringsbecoming even less distinct. Using the Adcom's "Bypass" outputs rendered the bass very much closer to the sound of the Mod Squad unit and brought back a degree of the hall acoustic, though the sound was still sweeter/darker than via the passive unit.
To put this performance into perspective, I have found this comparison to be cruel to any active preamplifier: the Adcom's departure from neutrality from its Bypass outputs, while noticeable, was, in absolute terms, relatively minor.
I didn't have access to Stereophile's sample of the Audio Research SP11 with which Gary had compared the '565; rather, I set up a comparison of the Adcom's line stage with that of the $5035 Mark Levinson No.26, this time with either feeding the Classic 60 power amplifier. As might be hoped from its price, the Levinson preamp more closely approached the paradigm set by the Line Drive. Its soundstaging was as well-focused and only slightly less deep, the ambience on the Stereophile CD guitar and bass recording being only a little more reticent. Tonally, its sound was identical to the Mod Squad unit through the midrange and treble. Its low frequencies were as well-defined, but had more impact, more weight, than the passive unit, to the benefit of the music. By comparison, the Adcom came over as more dark-sounding, which lent music a rather uninvolving quality. Again, however, considering the Adcom's price, it did very well in this comparison, its departures from perfection being both minor and subtractive.
Finally, I compared the sample of the GFP-565 that Gary reviewed with the second sample. If anything, the soundstage reproduced by the newer sample was deeper, with better presentation of recorded ambience. Other than this, there were no major differences, suggesting that the '565's qualities will be just as available to its purchaser as they were to the reviewer.
To sum up, the Janus-faced GFP-565 can either offer a Class B or a Class C sound, depending on whether its owner wants to use it as a basic, no-frills preamplifier via its Bypass outputs, or as a full-featured control center via its Main outputs. Its line stage is somewhat dark-sounding in absolute terms, though its low-treble balance did push some instrumental images forward. It has good midbass weight via its Main outputs, though its overall low-frequency performance lacks definition. Via its more transparent Bypass outputs, and particularly when used for LP replay, the '565 offers superb sound quality, with well-defined low frequencies. Used as a basic, no-frills preamplifier, therefore, Adcom's GFP-565 is a sonic bargain.John Atkinson