Naim NAC 552 preamplifier:
Page 2 According to design team leader Roy George, careful listening has convinced Naim's designers that microphonics have a profound effect on sound quality, even in solid-state gear—which won't be surprising to most Stereophile readers. After careful listening, they've concluded that suspending the circuit boards on springs has an audibly positive effect. Removing four transit screws allows the four boards, arranged in vertical pairs and separated by pillars, to float on spring suspensions. The boards are attached to heavy brass plates that add sufficient mass to lower the resonant frequency of the spring suspension to offer effective isolation. As the resonant frequency goes down, the length of travel of the springs increases.

On removing the NAC 552 from the box, you are advised to unscrew the four transit screws from the chassis bottom and to then not turn the unit over. Turning the unit over with the suspensions free would probably cause the weighted boards to bang into the chassis cover. I hung my sample off the edge of a chair to access two of the screws, then turned it around to remove the other two without having to turn the unit over.

The preamp functions are divided among the boards: one pair handles input switching and driver circuitry, the other buffering, gain, and a filtering stage. All components, including the bipolar transistors, are discrete and, according to Naim, "expensive" parts not usually used in audiophile gear. Careful listening determined ground-plane and parts placement on the circuit boards.

After carefully considering ladder-resistor volume controls, Naim chose a high-quality conventional ALPS pot. Roy George told me that this was what sounded best, though only after careful mounting to minimize microphonics.

One of the NAC 552's most interesting features is a steep filter, well out of the audioband, designed to limit super-fast risetimes and prevent out-of-band fast transients from reaching the power amplifier. Naim contends that when an amplifier is fed waveforms that are "faster" than it can handle, there are negative consequences in the audioband. They claim that the "constant time-delay filter" used has no negative effects on the sound.

The fit'n'finish of the two boxes is exceptional, and much improved over other Naim products I've had in for review, which were solidly built themselves. Naim's familiar industrial design aesthetic has been maintained, though the NAC 552's sculpted front panel, backlit buttons, and satin-smooth finish make it more pleasing to the eye and less of a forbiddingly monolithic black box. It's possible to turn off the front-panel lighting by pushing the Disp button on the remote. Should you thereafter change any front-panel function, the LEDs will temporarily illuminate, then go out again. Push Disp again and the lights stay on.

Supplied with the NAC 552 is Naim's Flash, an ergonomically pleasing remote control that's backlit and equipped with an LCD screen that can operate other Naim gear, and can be set to switch to the appropriate preamp input. If you want to operate a Naim CD player with the Flash, the NAC 552 will automatically switch to the appropriate input. The remote's backlighting switches on as soon as you pick it up, and automatically goes out when you set it down—a handy feature.

Also extremely useful are the remote's triple-action volume and balance buttons: a quick touch and release results in a very small movement. Press, release, and then press continually causes the volume or balance control to move smoothly but slowly. A single press and hold causes the control to move quickly. These variations came in very handy.

Setup and Use
After running the two umbilicals from the NAC 552PS to the NAC 552, I connected the dCS Verdi, Purcell, and Elgar Plus SACD and CD-to-DSD playback system to one of the RCA inputs, the Manley Steelhead phono preamp to the other. Naim supplied a Chord DIN-to-RCA cable, which I used for my McIntosh MR-67 FM tuner, and a four-plug, in/out RCA-to-DIN connector for the Alesis Masterlink's analog inputs and playback jacks. Naim also supplied their Stageline phono preamp, configured for a low-output moving-coil cartridge, and which I connected to the powered DIN socket. Since the Stageline is driven by the NAC 552PS power supply, it's both compact and relatively inexpensive ($350). I connected to it the combination of Graham 2.2 tonearm and Audio Tekne MC-6310 cartridge.

After switching on the NAC 552, I assigned each of its jacks to a source button (the Record Out buttons follow automatically) and sat down for a first listen. Chris Koster said that the 552 needs considerable break-in—µp to a few months—to sound its best, and for the capacitors to settle. I had only about a month. "You'll know," he told me.

The one glitch I found in the NAC 552 was that static discharges would cause all of its source LEDs to light up. Fortunately, the selected source for listening or recording did not change when that happened, and a touch of the selected source button would extinguish the other LEDs. Naim is aware of this problem; Koster told me that they have a fix.