Spin Doctor #16: Sutherland Dos Locos Phono Preamp, Dynavector XX-2A Phono Cartridge

Ron Sutherland makes a strong case for being crowned the king of all phono preamps, though I expect he would blush at any such suggestion. In 1979, with degrees in physics and electronic engineering (where his final project involved designing and building a digital logic–controlled preamp), he teamed up with Gayle Sanders to found electrostatic speaker company MartinLogan. (“Martin” and “Logan” are Sanders’ and Sutherland’s middle names, respectively.) But after a few years, he found the increasingly corporate mindset at M-L a bit stifling, so he decided to go his own way. Ron wanted to build gear he thought was cool and fun while not being directed solely by its commercial potential. He joined up with his brother to start Sutherland Engineering, creating hi-fi equipment that piqued his own interest and hopefully that of a bunch of customers.

At first, Sutherland made a wide range of components, including preamps, power amps, and DACs, but gradually he focused more and more on phono preamps. Today that’s the only thing he makes (footnote 1).

The $9800/pair Dos Locos is Sutherland’s latest and most ambitious in a series of phono preamps that use transimpedance (current drive) to amplify the cartridge’s electrical signal. The Dos Locos follows the Phono Loco ($8200; reviewed by Michael Fremer), the Little Loco Mk2 ($3800), the Big Loco (not reviewed and apparently no longer available), and the SUTZ head amp ($3800). The Dos Locos is “dos” because it comes (for stereo systems) as a pair of independent monoblocks. Mono listeners can buy just one (Uno Loco?) for $4900.

Transimpedance phono preamps take the conventional voltage-gain method and flip it on its head, connecting the cartridge across a dead short, then measuring the current of the signal reaching the input and converting it to voltage. Because the load is effectively zero ohms, there are no loading options, and the gain cannot be described in decibels as in a voltage-gain device. Sutherland notes that the gain can be clearly specified in terms of ohms, which makes sense: How much voltage is generated for a given current? The mechanism here is a bit different from the familiar case (a current passing through a resistor), but the answer still depends on an impedance. Herb did a great job of describing what transimpedance is in Gramophone Dreams #70 (footnote 2) if you’d like to explore the topic further.

Sutherland’s designs are striking for their simplicity and single-mindedness, polar opposites of phono preamps with lots of features, connections, and controls, such as the Mola Mola Lupe and CH Precision P1. There are no external switches on either of the Loco chassis—just a simple aluminum faceplate in silver or black, with a blue LED power indicator at one end. Around back are four RCA sockets, two for the input and two for the output.

Wait, dual inputs and outputs but no switches? How does that work? The dual outputs are there so that you can feed the Dos Locos’ output to two components at once. The twin inputs are there to allow you to connect two phono cartridges—though of course you would only play one of them at a time. Sutherland’s insistence on signal-path purity—put nothing in the circuit that you don’t have to—led him to leave off a selector switch; he can get away with that because of how transimpedance works: A zero ohm input impedance means that each connected cartridge doesn’t affect the other (footnote 2).

Each Dos Locos comes with a medical-grade power cable that appears to be a notch above the generic “starter” cables supplied with most components; it connects to an IEC power socket on the back. There is no power switch; with their modest 10W power draw, the Dos Locos are designed to be left on. I left them on throughout the review period, and after a couple of weeks, they were just barely warm to the touch.

This simplicity reminds me of my Vendetta Research SCP-2B phono preamp, which also has no controls of any kind and can only be switched off by unplugging its two power cables.

Lifting the cover on the Dos Locos reveals the obsessive attention to layout and signal routing we have come to expect from Sutherland. Inside, the chassis is split into two sections with a wide-open gap between the primary power supply on the left side, and the final power supply caps and the signal circuitry on the right. I fibbed a little bit when I said there were no controls, because on top of one of the signal circuit boards you will find a three-position jumper to adjust gain. This is a conventional, secondary gain stage; the volume steps seem to be about 6dB. I kept it in middle position, as set at the factory.

Due to the very nature of transimpedance phono stages, it is hard to know exactly which cartridges will work best; in my investigations, it has proven to be a bit of a “try it and see” exercise. A low coil impedance is the most important factor (footnote 3)—that much is clear—and Sutherland says any internal resistance below 20 ohms should be fine. This rules out even some of the low-output MCs from Benz Micro’s range, and certainly most high-output MCs and, eg, the Denon DL-103. It also rules out all moving magnet cartridges. I used a Lyra Atlas λ Lambda (4.2 ohms internal impedance) and a Dynavector DRT XV-1s (6 ohms), and while my Atlas isn’t the ultralow–impedance SL version, its internal impedance of 4.2 ohms is plenty low, and both it and the Dynavector seemed a fine match with the Dos Locos.

Most jazz aficionados are familiar with the West Coast record label Contemporary Records, but fewer know that Contemporary sublabels issued recordings of classical chamber music. The Contemporary Composers Series includes about a dozen albums of works by composers from the mid–20th century, often featuring the composers themselves as performers. Many of these were engineered by the legendary Roy DuNann, who is famous for his recordings on the jazz side of Contemporary Records.

I played William O. Smith: Four Chamber Works (Contemporary S 8010), a spectacular recording. As a jazz clarinetist who collaborated frequently with Dave Brubeck, he went by the name Bill Smith, but for his classical composing and performances he went with this more formal version of his name. The record jacket doesn’t disclose the recording location, but I wouldn’t be surprised if this was done at Contemporary’s legendary shipping room/recording studio at their headquarters in Los Angeles, as the recording has a similar, fairly dry acoustic. With the Atlas playing the Quartet for Clarinet, Violin, Cello, and Piano through the Dos Locos, all the typical Roy DuNann sonic characteristics were clearly on display: The astonishingly accurate tone of each instrument, especially the violin and Smith’s clarinet; the natural attack of the string plucks during pizzicato sections; and the huge, open soundstage. Contemporary’s jazz recordings sometimes suffered from instruments wandering around the soundstage—I suspect that the jazz musicians were standing and moving a bit as they played—but there’s none of that here. Each instrument is clearly and consistently positioned, and solid. Helping bring all this transparent detail into clear relief is the Dos Locos’ incredibly low noisefloor, a typical characteristic of transimpedance phono stages but especially apparent here.

Shifting gears, I put on drummer Paul Motian’s On Broadway, Vol. 2 ( JMT– 834 440-1), a jazz quartet with sax player Joe Lovano, bassist Charlie Haden, and guitarist Bill Frisell. On “You and the Night and the Music,” Haden’s bass drew my attention first, with a clarity of pitch you rarely hear from recordings of this instrument. I saw Haden playing live with Motian many times—both are gone now, sadly—so I know Charlie’s bass sound. It is hard to reproduce, ill-defined and dull through the wrong setup. Not here! Each note was clear and unencumbered, making his line easy to follow. Motian plays with a light touch, dishing out a beautiful range of tones and colors from his array of cymbals.

Paired with the right cartridge, the Dos Locos is an extraordinary performer. Its tone has the purity of fresh snow, and it manages to sound highly resolved yet, at the same time, unstressed and relaxed. It’s as quiet as any phono stage I’ve encountered, framing its sonic capabilities in an even more dramatic way. This one sings!

Footnote 1: Sutherland Engineering, 455 East 79th Terr., Kansas City, MO 64131. Tel: (816) 718-7898. Email: [email protected]. Web: sutherlandengineering.com

Footnote 2: This would not work with a voltage-gain preamp, but it does work with a transimpedance preamp. Here’s how.

In basic circuit theory, the phono cartridge coil can be modeled either as a voltage source with a series resistance (Thevenin equivalent) or as a current source with a parallel resistance (Norton equivalent); the two approaches are effectively the same and will yield the same result, so you can choose whichever approach makes the calculation easier. The former works best in modeling a voltage-gain preamp, the latter when modeling a transimpedance preamp.

When connected to the transimpedance preamp, a coil “sees” a short circuit: zero volts, zero resistance.

Now assume that two cartridges are connected in parallel, each modeled as described above, but only one is “in the groove.” There is no voltage at the input (it’s a short circuit) and no changing magnetic field in the inactive coil that would cause current to flow. The innactive coil, then, can have no effect on the active coil.

“This was not a design goal,” Ron Sutherland told me. “I just figured it out as a way of adding a second cartridge without compromise.”—Jim Austin

Footnote 3: It almost seems paradoxical: Low impedance in the loop means higher current, which means higher voltage via the transimpedance “gain” stage. Perhaps the most important idea here, though, is that there’s nothing to resist a change in current—hence, nothing to restrain the motion of the coils through the permanent magnetic field.

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