Descriptions of the sounds of products from Sutherland Engineering nearly always include “refined.” While that word is certainly justified, it would be more apt to use it as a verb: Ron Sutherland spends more time than any audio designer I’ve known studying and fine-tuning and refining every detail of his work. I have the impression he knows those products so well that when he decides to design a less expensive version of his newest and best models, he knows exactly what to do.

The Sutherland Duo phono preamp I reviewed in August 2017 is a case in point. It sells for $4000 and comes within a hair of matching the performance of the $10,000 PhonoBlock Refined. It even betters it in a few ways. So when I heard that Sutherland was introducing a “trickle-down” version of the cost-no-object Phono Loco phono preamp, I muscled my way to the head of the line for a review sample.

Transimpedance 101
The Little Loco and the Phono Loco differ from Sutherland’s other models in being current-mode designs, other examples of which include the CH Precision P1 (which Michael Fremer uses as a reference, footnote 1), the Channel D Lino C 2.0, and the Haniwa HEQA03-CI (see this issue’s Analog Corner). But the technology is not as well-known as that of voltage-mode phono preamps, so the distinction bears repeating:

An MC phono cartridge can be modeled as either a voltage source or a current source; conventional phono preamps take the former view: The movement of the cartridge’s coils through its magnetic field creates a small voltage that pushes a current through the internal resistive load of the attached phono preamplifier.

Current-mode phono preamps view the cartridge as a pure current source, ignoring voltage, and aim to impede that current as little as possible. A typical strategy is to use an op-amp to mimic a short between the cartridge’s two terminals; the cartridge thinks current is flowing freely, but it is actually diverted through a feedback resistor connected between the op-amp’s input and output terminals. The voltage drop across that feedback resistor is measured, amplified further, RIAA-corrected, and sent on to the rest of the audio system for conversion into music.

Opinions vary, but there’s general agreement that current-input phono stages have two advantages. One is inherently low noise: Because there’s no voltage associated with the musical signal, it’s immune to several vexing noise sources—for example, those that result from the mechanical and electrical weaknesses of phono cables. A second claimed advantage of transimpedance designs is their demonstrably faster real-world response at similar levels of effective gain; this difference provides better damping and allows a cartridge to respond more quickly and accurately to the smallest variations in a record groove.

On the other hand, a current-mode phono preamp limits choice in some ways. The shield and ground of the phono cable must be isolated from the plus and minus conductors, which eliminates certain cables and tonearms from consideration. There’s nothing a user can adjust to optimize the circuit for a certain cartridge—no adjustment of load resistance, in other words. You’re almost entirely limited to moving-coil cartridges, and apparently, even among moving-coils, some combinations don’t work at all. Got a cartridge you want to use? Plug it in, hold your breath, and see what happens.

A little loco
The Little Loco shares its cosmetics, fit and finish, and build quality with other Sutherland models, which is to say, it’s refined. I’ve never seen a Phono Loco, so I contacted Ron Sutherland to learn how the Little Loco differs from its big brother. “Everyone loved the Phono Loco, so I started thinking about how I could do it for less money. It’s a challenge, but one that I really like. A lot of it was power supply and filtering. The Phono Loco has completely separate power supplies (for the two channels) and . . . separate power supplies and filtering for each gain stage.” In contrast, the Little Loco has separate power supplies for each channel after the transformer, but not for individual gain stages.

Sutherland continued: “Because of the smaller power supply, I could use smaller boards and a smaller chassis. The Little Loco actually uses the same chassis as the [Sutherland Insight phono preamp], so I didn’t have the expense of building a new one.” I asked, “If you’re reusing an existing chassis, why design a whole new power supply?” After all, you can buy cheap ones off the shelf, such as the one he used with the Sutherland Duo. His answer: “Oh, I just thought it should have a linear power supply.”

Is it not for everyone?
In most manufacturers’ product descriptions, “It’s not for everyone” usually means one of three things: that the product is unreasonably expensive; that its operation is so convoluted that the effort required to play music becomes excessive; or that its sound is an acquired taste, appealing to a few but sufficiently odd to be considered a fail with respect to established criteria and metrics. In these respects, that phrase does not apply to the Little Loco.

The first two of these concerns are easily dispelled. At $3800, the Little Loco isn’t cheap, but its price is in line with those of other products in its class. Second, its use could not be more straightforward, even if it isn’t universally applicable. True: Your tonearm wiring must be fully balanced between cartridge and phono preamp, with no connections between any of the tonearm leads and ground. That means that the Little Loco won’t work, for example, with your Rega arm, unless it’s rewired. Yet there are no adjustable parameters, options to choose from, or controls of any sort— not even a power switch (footnote 2). You connect the input and output cables, plug it in, and play music.

When I did that, the third possible interpretation of “not for everyone” vanished, too: Its sound was about as far removed from “acquired taste” as I could imagine. It was love at first listen.

Ah, but there’s a fourth
So the Little Loco is reasonably priced, trivially easy to use, and sounds wonderful. But don’t buy a Little Loco to use with a moving-magnet cartridge—”their performance is awful into a short,” Sutherland says. And MMs aren’t the only cartridges that won’t work with the Little Loco.

I tried pairing the Little Loco with six cartridges: an Audio-Technica AT-OC9ML/II, Grado Statement Reference, Lyra Titan i, Benz Micro SL, My Sonic Lab Ultra Eminent Ex, and, just for fun, an Audio Technica AT-MO-NO3/LP. On paper, the AT-OC9ML/II, Titan, and Benz Micro—all moving coils—are very similar, each with an output of about 0.5mV, internal impedance around 10 ohms, and a dynamic compliance of about 10×10^–6cm/dyne. The moving-coil My Sonic Lab Ultra Eminent Ex has similar specs for output and dynamic compliance but an impedance of only 0.6 ohms.

The AT-MONO3/LP has two coils that are built to respond to horizontal motion only, and the negative output terminals of those two coils are connected. Because of the connection, it shouldn’t have worked with the Little Loco— and it didn’t: All I heard was a loud, threshold-of-pain hum underlain by music signal at the limits of audibility.

The Grado is neither moving-magnet nor moving-coil: It’s a moving-iron cartridge. The Phono Loco website says that moving-iron cartridges won’t work with the Phono Loco, but the Grado Statement Reference sounded as good through the new Sutherland as through a more typical phono preamp—although it did not benefit from the Little Loco as much as the Benz Micro, My Sonic Lab, or Audio Technica AT-OC9ML/II did. I had to connect the ground lug of the Little Loco to the one on my turntable to eliminate hum, but that was all it took.

Ostensibly, my success with the Grado contradicts the Sutherland Engineering website, but it corroborates something Ron Sutherland told me: The Little Loco is unpredictable. “I want people to be comfortable that transimpedance (or current input) phono preamps have some frontier exploration aspects,” he wrote in an email. “I suggest the potential buyer work closely with a dealer very experienced with Loco/cartridge matching.”

Footnote 1: Published in Analog Corner in the April 2017 issue.

Footnote 2: You can adjust the gain by replacing two resistors inside the box, but I don’t count that as a control.