Solid State Preamp Reviews

Like most serious pursuers of the audio hobby, I've known about J E Sugden & Co. Ltd. for years. For many of those years, though, it was easy to forget about them, and I mostly did—until, quite recently, Sugden gear began popping up at audio shows, including the 2016 Rocky Mountain Audio Fest. In his report on that show, Herb Reichert described the midrange of Sugden's A21SE Signature, a pure class-A integrated amplifier, driving DeVore Fidelity speakers, as "shroom-like" and contrasted the sound with what he called class-D's "fake cocaine." That got my attention.

Sugden again showed up at RMAF 2017, this time with different DeVore speakers driven by Sugden separates, including the Masterclass LA-4 line preamplifier ($3750). Because I've been making a study of preamplifiers, listening to as many as I can lay hands on, I decided to give that model a listen.

J E Sugden & Co.
Fun audio fact: The first patent application for an audio amplifier based on field effect transistors (FETs) was submitted in 1928, by Polish physicist Julius Edgar Lilienfeld, who patented the electrolytic capacitor. That's fascinating because the transistor itself was not actually invented until 1947. Lilienfeld's patent was based on a then-hypothetical device that scientists didn't yet have the ability to make.

The first practical transistor-based audio amplifier was presented at a conference at the University of Pennsylvania in 1955, by Richard F. Shea, a GE nuclear scientist and radio engineer. Shea brought along a turntable and an Altec Lansing 601 studio monitor speaker: a 12" coaxial drive-unit in a bass-reflex box. This very first transistor-based amplifier, housed in a plain metal box and notable for its smallness, included a phono stage with an RIAA filter. At the end of his presentation, Shea played an LP. Everyone got up and danced. (I made that last part up, but the reception was, reportedly, enthusiastic.) Shea's amplifier circuit featured class-B output-stage bias.

The early 1960s were to transistors approximately what the 1990s (or maybe the '80s) were to microprocessors, with new, improved versions appearing often, at ever-lower prices. Designers of other early solid-state audio amplifiers mostly followed Shea's class-B example, because the transistors then available were made from germanium, and germanium-based transistors didn't deal well with the heat associated with class-A biasing. The sound quality of those early class-B transistor designs couldn't measure up to the tubed amplifiers of the time.

James Edward Sugden launched his first company, Research Electronics, in 1960, to build test equipment for universities. It was the height of the cold war, and nuclear radiation was, um, hot—his company made parts for radiation detectors. But Research Electronics made more mundane stuff as well: low-distortion oscillators, high-precision voltmeters, an instrument for measuring amplifier distortion. Interested in audio, Sugden soon became obsessed with the problem of crossover distortion—the main kind of distortion that caused class-B solid-state amplifiers to underperform, especially at low signal levels.

Introduced commercially in the mid-1960s, planar silicon transistors had better voltage and temperature stability than their germanium predecessors. Sugden, who had access to state-of-the-art test equipment, saw the potential to make better-sounding transistor amplifiers. Like Nelson Pass in a later generation, he returned to tube-inspired strategies—specifically, class-A design. Sugden wrote about his class-A amplifier prototype, the Si 402, in an article in Hi-Fi News in 1967, a time when audio magazines were still wonderfully wonky. Using his sensitive distortion meter, Sugden compared the Si 402 with an otherwise-identical class-B design he called the Si 403. The Si 403's distortion, he showed, remained constant as the volume was reduced—hence its harsh sound at low volumes—while the class-A Si 402's distortion tended toward zero as the output power declined.

That same year, Sugden established J E Sugden as a division of Research Electronics. Its first product was a 6Wpc integrated amplifier, the A21, a version of which is still in production today, 52 years later. The A21 was, by historical consensus, the world's first class-A, transistor-based audio amplifier. A few months later, J E Sugden introduced the A41 power amplifier and the company's first preamplifier, the C41.

The Masterclass LA-4 preamplifier
James Sugden's achievement was in power amplification, but that historic effort signifies the level of perfectionism he brought to his early preamplifiers, as well: Unsurprisingly, those preamps—designed with the aid of his own sensitive test gear—were also technically accomplished, with low distortion and wide bandwidth. They also, as was then typical, had lots of features: tone and balance controls, mono switches, and loudness controls. And, of course, they had phono stages—the main purpose of a preamplifier back then—which indeed were quite flexible, with in-line adapters and rear-panel plugs to support nonstandard phono cartridges and RIAA curves.

Step forward to the present day. The Masterclass LA-4 is not full-featured but minimalist. It's line only—no phono. It has inputs for up to five sources, all but one with unbalanced connectors (RCA). The Bypass input sidesteps the volume control, and an output with the antiquated label Tape bypasses the volume control for whichever input is selected. There's a Standby button on the front panel and a main Power switch in back, because transistor-based amplifiers—including preamps—sound best when they're always powered up. There's a source-selector knob, a Volume knob, and a Record button—other than the tape loop, just the basics. The remote control is basic in a different way: cheap-looking plastic intended, apparently, to be used with a CD player, and useful with the LA-4 only to adjust volume.

The LA-4 has just one balanced input, so I was surprised to learn that the preamplifier circuit is fully balanced; Sugden sent me a diagram to prove it. When I asked the Sugden folks about this balanced circuit design, I got an answer I thought was interesting: "We describe it as a virtual transformer," the rep told me by e-mail. "The idea is based on something similar to a [step-up transformer] for a moving-coil cartridge but at line level with one input and two outputs plus a center tap to give a balanced input/output." His use of "transformer" is more metaphorical than anything else—the only actual transformers in the LA-4 are in its power supply—but, sonically, I found the comparison between the LA-4 and a step-up transformer apt. About which more in a bit.

Input switching on the LA-4 is done via relays, which should be as transparent as wire, or nearly so. The volume control is old-school, and the knob's action felt creamy—not as good as some old tuner knobs, but with a better feel than any new-tech, stepped volume control I can recall turning. I like a volume control with a good feel. In contrast to those more modern attenuators, it's continuously adjustable, with no discernible steps. That proved useful: The LA-4's gain is high for my main amplifiers, the PS Audio BHK Signature 300 monoblocks, so big volume steps would have made it hard for me to adjust the volume precisely. Not a problem here.

The LA-4's output stage is class-A, as you'd expect for a preamp. The specified bandwidth is wide: 6Hz–300kHz. The specified distortion is low: <0.006% at 1kHz, 1V out. Visually, the LA-4 is simple, chunky, rugged yet sleek. It feels solid, giving the impression—reinforced by the brand's reputation—of a component that will provide many years of flawless service. Looking vaguely industrial in a standard finish of silver or black, the LA-4 is also available, for a $250 upcharge, in 16 other colors, including violet, turquoise, and three shades of green. These bright, unusual colors change the look from handsome but conventional to something much more interesting and playful. (I'm fond of the matte black they call Stealth, with matching knobs.)

Vintage Methodology
There's nothing especially vintage about the Masterclass LA-4, but reading about Sugden's early days inspired me to delve deep into Stereophile's on-line archives, reading reviews of tube preamplifiers and solid-state preamplifiers dating back to the 1960s. My research focused mainly on reviews from the mid-'80s, as the LP was fading and more attention was being paid to preamplifiers' line-level than phono capabilities—the latter its own can of worms, and irrelevant to my current task.

Stereophile's reviewers were energetically exploring preamps in the mid-1980s, aiming to discover and name the then state of the art. They uncovered a handful of models—eg, the Counterpoint SA-7—with obvious inadequacies. Near–state-of-the-art preamps encompassed two types: those that approached transparency ("straight wires with gain," in Quad founder Peter Walker's phrase), including the Audio Research SP-11 and the Klyne Audio Arts SK-5A, and those that made music sound better than music really sounds, including the ARC SP-10 and the Conrad-Johnson/Motif MC-7. Their reviews repeatedly raised the age-old questions: What's the objective of an audio system? What should reproduced music be compared to?