Variable gain power amplifiers have always made a lot of sense to me from a sonic, if not always a practical, standpoint. Including a gain control to vary the voltage output of the amplifier approaches the ideal of a straight wire with gain. Talk about a simple, direct circuit. What could be better? No need to worry about “polluting” a delicate preamplifier section within the amplifier itself, as in the case of an integrated amplifier, or having a run of interconnects to a separate preamplifier, along with the associated connectors. I suspect variable gain amplifiers have not really caught on as much as they deserve for one simple reason: People typically have more than one source.
Enter the control amplifier, essentially a set of input selector switches and a variable gain power amplifier. It’s easy to think of it as an integrated amplifier, because from a user perspective, it operates essentially in the same way. However, a control amplifier and an integrated amplifier are somewhat different animals, as control amplifier proponents are quick to point out. Whereas the typical integrated amplifier has multiple gain and buffer stages, the control amplifier completely eliminates the linestage and its inherent colorations. With its new GCC-100 ($2795), PS Audio goes one step further. It doesn’t have a standard volume control, like a stepped attenuator or a volume pot which introduce noise, but uses a unique approach to controlling gain that is said to add no audible noise and little to no distortion. Coupled with a Class D output stage, it results in a direct, clear sound that many will find appealing.
The brainchild of one of PS Audio’s original founders, Paul McGowan, the Gain Cell is the culmination of his twenty- five year quest to develop a perfect gain stage, and the circuit is used throughout PS Audio’s new line of components. While details on it are a trade secret, and the unit is fully encased to keep the prying eyes of competitors away, PS Audio says that it is fully balanced from input to output, is 100% analog, has flat bandwidth from 1Hz to 50KHz, and adjustable gain from -100dB to 30dB. Better still, the performance of the Gain Cell is reported not to vary with gain, which can be adjusted instantly and in increments so small as to be undetectable by the human ear.
So what does one do to control volume on the GCC- 100? Gain is adjusted via a knob on the front panel or from the remote control, and the volume level is displayed on a blue-lit fluorescent panel. I like the ergonomics of the GCC-100, with its blue lights and gently curved lines, and it looks great in the same cabinet as my Musical Fidelity Tri- Vista 21 DAC. The soft blue lights emanating from both give me some of the visual thrill I get from tube amplifiers in a darkened room. If the GCC-100’s lights distract from the listening experience, you can either dim them or turn them off completely. The unit is a dualmono design, with one Gain Cell per channel. The slim remote offers great functionality, allowing you to adjust phase and balance from the listening position, as well as switch inputs. It also includes a home-theater bypass that enables you to control the GCC-100 via a surround processor.
This control amplifier’s “direct” approach results in stunning transparency. Borrowing an HP analogy, it’s as if the window onto the soundstage has been thoroughly cleaned with Windex. There is no sonic glaze or dirt between you and the performers. This results in a very open, clear sound throughout most of the sonic spectrum, particularly in the bass and the midrange. The quietness of this unit undoubtedly contributes to this.
Another area where the GCC-100 excels is in the bass, which is extended and dynamic, and has transient quickness and richness without any overripeness. String bass on both jazz and orchestral recordings had naturalness, solidity, and outstanding neutrality.
This control amplifier is also said to work with difficult loads, so I paired it with my restored Quads. While transparency was very good with the dynamic speakers I tried, the Quad/PS Audio combination was on another level. The GCC-100 seemed to really lock in with the Quads—not an easy task for many amplifiers. What’s more, it was able to draw more bass out of them than most amplifiers do, but this didn’t come at the expense of neutrality nor did it impinge on the purity of the midrange. With this combination, when listening to very good live recordings, like Hugh Masekela’s Almost Like Being in Jazz [Straight Ahead/Classic Records], I felt as if I could reach out and touch the performers. And there was also that outstanding bass performance with great definition, richness, and control. No need for a subwoofer here.
The GCC-100 is perhaps more like a chameleon than just about any piece of gear I’ve heard. You’ll need to be careful what you feed it, because this is one unit that doesn’t sugar-coat or caramelize anything. You’ll be rewarded by using better source material, front-ends, cabling, and cleaner power. Unfortunately, many new popular recordings have tilted-up mixes—a common technique in recording studios these days—and you’ll hear this as some forwardness in the upper midrange. On well-recorded material, the forwardness disappears.
Unfortunately, the highs of the GCC- 100 do not match the performance of the amp in the bass and the midrange, sounding somewhat dry and lacking in sparkle and life. What I missed were the fully fleshed out overtones that contribute to the natural timbres of instruments and female voice. Also, despite its very good image focus, many of the ambient cues of the recording space that one hears with other electronics were missing. It was as if the music was recorded in an anechoic chamber rather than a hall. Depending on your listening habits, particularly if you tend towards popular fare recorded in sound booths, these sound-cue omissions may not matter to you.
So how does the GCC-100 compare with a similarly priced integrated amplifier, like the Ayre AX-7e that impressed our Editor-in-Chief Robert Harley in Issue 144? In contrast to the Gain Cell/Class D approach of the PS Audio, the Ayre combines a passive linestage with a class A/B output section and uses discrete metal-film resistors and FET switches to control volume. Thanks to my friendly local audio dealer, I was able to compare them at some length for an afternoon using a variety of fine reissues: Ella Fitzgerald Sings Songs From Let No Man Write My Epitaph [Verve/Classic], Bach’s Suites for Unaccompanied Cello [Mercury/Speakers Corner], de Falla’s Three Cornered Hat [Decca/Speakers Corner], and Ben Webster’s Soulville [Verve/Speakers Corner]. 
As one might expect, the PS Audio control amplifier was somewhat better in terms of bass control, definition, and power, although the Ayre was no slouch in these areas. The GCC-100 had slightly better transparency, but the Ayre was able to render a better sense of the hall and of the back of the soundstage, and had better musical timbre and more satisfying highs. While the midrange of the PS Audio was slightly more open, the Ayre was more relaxed, with more natural warmth and bloom. Both of these fine units lack the ultimate richness and air around the performers of my reference tube electronics, but the Ayre came closer, and I ultimately preferred it.
The GCC-100 is likely to generate some controversy in audiophile circles. While its overall performance didn’t float my boat, I encourage you to listen for yourself. For many, this control amplifier’s direct sound, with its startling transparency and bass performance, will be a revelation.
 Thanks to Brian Hartsell at the Analog Room for lending me one of his listening rooms for an afternoon and to Scott Barnhill for his kind assistance.