Solid State Preamp Reviews

It's often been said that the best standard for determining the sound quality of a stereo system is the sound of live acoustic music. This idea appeals to me: I listen to a lot of live acoustic music, more, in fact, than anyone I know, in venues ranging from Carnegie Hall to my own listening room. The idea, however, is fraught. Because every step in the recording chain alters the sound, it isn't ever possible to know what a recording sounds like; logically, the sound coming from your speakers should sound live only if the music on the recording sounds live.

But even under the best circumstances—let's say you personally recorded, mixed, and mastered a recording to the best of your ability—you still don't know exactly what sound is on the record, because you've heard it—the recording—through headphones or studio monitors, reproduced and amplified by electronics. Even if, under those circumstances, it closely resembles what you heard live in the room, you still can't be sure you captured it. "How, then, do you tell what a disc is supposed to sound like?" asked J. Gordon Holt in 1977 (footnote 1). In a different piece, JGH suggested holding a record up to your ear. It doesn't have an intrinsic sound, does it?

If you listen to a recording a lot through many different systems, you can begin to know what that recording sounds like. You get a sense for a sort of average of its sound through the systems you thought sounded most "right." There's some circular reasoning there, but let's be generous and call it self-consistency. You can then note how, in a familiar system, that sound changes with one change of component, and thereby achieve a sort of differential diagnosis: of how a component sounds in comparison to other components you've heard. But this assumes that all of the other components in the system are pretty neutral, and are not offsetting each other's colorations. It goes on and on.

JGH and several other Stereophile reviewers from the 1980s understood this problem and wrote about it often. One innovation employed—it worked only for preamps—was the bypass test. Using a switch box, usually, (and for phono preamps, an inverse RIAA filter) they compared the sound with the preamp in the system to the sound with no preamp at all.

Today's DACs with excellent volume controls—eg, my PS Audio PerfectWave DirectStream DAC—make the bypass test easy to perform: Just match the volume precisely, and make sure the input and output impedances differ enough from each other that they won't significantly alter the tonal balance.

There are caveats to using such a methodology. (There always are.) I'll mention just one. Although differences revealed in quick comparisons inspire the most confidence, long-term listening can reveal differences that can't be perceived in short-term tests. It's a counterintuitive idea, and not everyone agrees with it. For a long time, I, too, was skeptical, but I've come to believe it. Differences that a listener—especially a focused, analytical listener—may not even be aware of may nevertheless influence that listener's experience of music. Anecdotal evidence for this is abundant—most open-minded listeners have experienced similar things—but there's also evidence in the peer-reviewed literature, in articles that evaluate listeners' emotional response to music, whether by advanced imaging techniques or simple Q&As.

This means that, while a bypass test can be useful, it's necessary to complement it with conventional long-term listening. So I did.

Listening
Jonathan Halpern of Tone Imports, Sugden's US distributor, told me that the Masterclass LA-4 needs a good bit of break-in, so I used it in my system for a couple months' worth of casual listening before beginning to listen closely. I did my long-term listening first, before conducting the bypass test.

My conclusions from my long-term listening are easy to summarize. At first, after break-in, I noticed a bit more ambience with good recordings via the LA-4 than with the preamplifier I'm most used to, my PS Audio BHK Signature ($5995). I noticed a touch less body than I get with the BHK, which has tubes in its input stage. I didn't notice a significant change in detail resolution or, apart from the slight increase in spaciousness, in subjective tonal balance. The soundstage, too, was much the same. Soon, though, I got used to the sound of my system with the Sugden in it. The differences I'd heard at first were no longer relevant; the music sounded as it sounded, which was very good: delicate, open, with detailed highs, rich mids, and rock-solid lows.

On to the bypass test.

I connected the equipment using either one or two sets of well-made balanced interconnects from Clarus Cables—their Crimson model—using the LA-4's balanced inputs and outputs. In bypass mode, a single set of interconnects linked the PS Audio DAC's balanced outputs directly to my BHK Signature 300 monoblocks. I wired the Sugden into the system in the usual way, using an extra set of Clarus Crimson interconnects. (For those who buy in to such things, both sets of interconnects have been in daily use for months: they're "burned in.")

With the preamp out of the circuit, I set the volume on my PS Audio DAC's digital output to "58." At that setting, the –20dB pink-noise track on Stereophile's first Test CD (Stereophile STPH002-2) yielded a volume at my listening chair of 75.0dB, unweighted, as measured by the AudioTools FFT app on my iPhone.

I put the Sugden preamp in the circuit and set its volume control to match that volume. Thanks to the Sugden's non-stepped volume control, I was able to achieve a volume-level match within 0.1dB with the knob set at about 1 o'clock. After that, I left that knob alone.

It's not always the highest-fidelity audio tracks that are the most revealing. First up was Sam Cooke's demo version of "You Send Me," from Sam Cooke's SAR Records Story, 1959–1965 (16-bit/44.1kHz stream, ABKCO 3122/Tidal/Roon). The apparent bandwidth of this recording doesn't much exceed 10kHz, but it illuminated the Sugden preamp's sound.

That word, illuminated, is apropos: As I heard it, the Sugden Masterclass LA-4 was not quite a straight wire with gain: it subtly illuminated the music. Consistent with my early observations during long-term listening, there was a touch more ambience to the demo's narrow-bandwidth sound with the Sugden in the system than with it bypassed. It was as if the upper midrange and presence region had been subtly boosted.

More Sam Cooke: "A Change Is Gonna Come," from his Ain't That Good News (16/44.1, ABKCO 98992/Tidal). This moving, frequently covered, historically important recording has some really strident strings at the beginning, especially in the left channel, but after that it sounded big and majestic in my system with the Sugden; the resonance of Cooke's voice, and the vital electricity in the space around him, were subtly accentuated. In bypass mode, Cooke's voice was still resonant and the space was still charged—it's recorded that way—but the sound was just a touch drier.

The more I hear it, the more I appreciate pianist Minoru Nojima's Nojima Plays Liszt (24/176.4 download, Reference RR25), both for its musical value and for the quality of its sound. This is a great recording by the esteemed Prof. Keith O. Johnson, with near-ideal balances of the instrument's body and percussive impact on the one hand, and direct and room sound on the other.

Nojima Plays Liszt has, however, a small and useful idiosyncrasy. On some tracks, including the first, Mephisto Waltz No.1, notes emerge from two separate planes: lower, louder notes from just behind the speakers; and softer, higher notes from several feet farther back. This is quite easy to hear—eg, just after the 15-second mark in this track. You'd expect, instead, the notes to come either all from the same plane, as a Steinway grand sounds in live performance from the front rows—or with the higher notes steadily farther back, as you'd expect from a recording that artificially enhances the piano's image with fancy miking techniques.

Whether the LA-4 was bypassed or in circuit, this sounded the same. The Sugden, in other words, preserved this anomaly intact, which shows that it preserved subtle soundstage cues. In my experience, such depth cues are among the first things to disappear when a component starts messing with a signal. Not a problem here.

At the other end of the audioband, Brian Bromberg's double bass was intense in his solo version of the Beatles' "Come Together," from his album Wood (FLAC from CD, A440 Music Group 4001). Bromberg's bass occupies a different range of frequencies from the Sam Cooke tracks, yet the LA-4's effect was much the same: Bromberg's bass seemed a touch more spotlit with the Sugden in the system, more lit up. Either way, with or without the preamp, his instrument was like a mighty oak, octobass-sized, and with rip-snorting impact.

I also thought the recording sounded louder through the Sugden, which led me to doubt my volume matching—a fairly small volume difference could have accounted for the differences I was hearing. I checked the volume-matching again with pink noise. It checked out.

Conclusions
I'm intrigued by the Sugden rep's invocation of a "virtual transformer"—specifically, a step-up transformer in a phono circuit. I realize that "virtual transformer" is mainly a suggestive, shorthand way of describing Sugden's circuit topology—no one from Sugden claimed any sonic parallels. But the LA-4's sound reminded me of what a good step-up transformer can do for the sound of a moving-coil cartridge. It added a touch of life, of light and color. The scientist in me says that fewer active devices should result in better sound; the music-lover hears improvement with the preamp in the system.

The Masterclass LA-4, then, belongs in that second category of good-performing preamplifiers reviewed in those 1980s issues of Stereophile: those that aren't the most absolutely truthful, but that make the music sound a little bit better. In this respect, it's similar to my main preamplifier, the PS Audio BHK Signature, though the BHK alters the music in a different but similarly subtle way. It's worth noting that, while explicit colorations typically make some music sound better and other music worse, I never heard the LA-4 make music sound worse. Whatever is going on, it's something more subtle than explicit tonal coloration.

The scientist in me also craves an honest preamplifier—a quest that our Michael Fremer has called "quixotic"—but again, that scientist loses out. In his 1991 review of Threshold's FET Nine/e preamplifier, Robert Deutsch attributed this statement to JGH: accuracy in audio reproduction is "the ultimate objective of an ideal sound system, which everyone claims they want but nobody likes when he has it." The longer I'm in this business, the more I believe that there's something a bit off about maintaining an analytical mindset while appreciating—enjoying—music. Gradually, I'm coming around to Holt's point of view.

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Footnote 1: J. Gordon Holt, "Who's Right? Accuracy or Musicality." Stereophile, December 1977.