Dos Locos Transimpedance Monoblock Phono Preamp

Dos Locos represents an extraordinary effort, Sutherland Engineering's first mono-block Transimpedance MC phono preamplifier. For those who've heard or been lucky enough to own one of Sutherland's magnificent Loco phono preamps, you know how stunningly musical and rich sounding these devices are. Deep black backgrounds, impressive depth of field and a tonal balance so present and alive you'd swear the performers are in the room. Dos Locos takes listening to vinyl to an entirely new plane of existence. Removing that final barrier between you and the music, Dos Locos opens a window into the recording so deep and real, this isn't listening to music, it's witnessing a performance!

Transimpedance Design
First some background, traditional Moving Coil (MC) phono preamps multiply the exceptionally low output voltage of an MC cartridge in an attempt to raise its output voltage up to line level. A typical 0.5mV (aka 0.005V) cartridge requires 4000% amplification to reach a nominal 2V line level output. This is a tremendous chore, fraught with the potential for noise. Because of this choice, a traditional MC phono cartridge must have multiple gain settings to match with a variety of cartridges and it must also have a number of impedance settings to match up with the various loading options any MC cartridge may require. Every owner of an MC cartridge has agonized over which settings to use on their phono stage, constantly worrying that they may not have selected the optimal setting.

There's a better way, though, Low output MC cartridges have an interesting characteristic! Although their output voltages can vary widely and tend to be exceedingly low, they all tend to have similar levels of current output. A transimpedance phono stage ignores the cartridge's output voltage and instead converts the MC cartridge's current output into voltage. This bypasses many of the issues of traditional MC circuitry including issues with Impedance Loading and Gain Matching. The transimpedance amplification method results in a much more robust signal, with greater integrity, lower noise floor and a much more involving listening experience. A good transimpedance phono stage is much more difficult to engineer than a traditional phono stage because of the huge reliance on the purity of their power supplies. This is where Sutherland distinguishes themselves from every other transimpedance design to date.

When it comes right down to it, the sonic performance of a phono preamp can ultimately be tied directly to the quality of its power supply. No matter how ingenious or innovative the amplification circuit might be, a mediocre power supply will deliver mediocre sound. However, a phenomenal power supply enables phenomenal sound! Sutherland Engineering takes great care in designing their power supplies and each Dos Locos channel receives its own full-size linear power supply. The entire left side of each chassis is consumed with this "motor", delivering all the ultra-pure power the signal side could ever require. On the right side, those enormous banks of capacitors serve two functions. First, they act as a low-pass filter, removing any remaining high frequency hash from the power chain. They also serve as an ultra-stable and ripple-free energy source for the tiny circuits handling the transimpedance conversion. 

Speaking of tiny circuits, like all Sutherland Engineering designs, the Dos Locos concept is all about simplicity, in service of ultra-high performance. With a single chassis handling each channel, noise is kept vanishingly low, signal integrity is incredibly high and channel separation is exceptional. Look inside the chassis, the circuit boards traces are clean, neat, meticulously organized and the signal pathways are kept very, very short. Take a peek at the top right corner of the circuit board, this is where all the transimpedance magic happens. From input to output these pathways don't run more than a few inches. By keeping the signal paths short, Sutherland minimizes distortion and maximizes signal integrity, all of which assures excellent sonic performance.

CARTRIDGE COMPATABILITY
Use only Low Output MC phono cartridges with less than 20 Ohms internal resistance. Dos Locos is NOT compatible with Moving Magnet, Moving Iron nor High Output MC cartridges. For a more in-depth explanation, please see the Compatibility tab.

GAIN
Transimpedance phono stages don't require traditional gain settings and their amplification isn't measured in dB like a traditional phono preamp. Dos Locos has plenty of gain for even very low output MC cartridges and most will work just fine on the MED setting. However, Dos Locos offers HIGH, MED or LOW settings, Just in case they're required. Our advice is to try MED first.

Dimensions: 17x13x2" Each (WDH)
Weight: 15Lbs Each
Voltage: US 117VAC only

The Dos Locos, like all transimpedance phono stages, is only compatible with Moving Coil cartridges and more specifically those with an internal impedance at or below 20Ω. For those interested in a more detailed explanation, we provide the information below. For those who are less technically inclined, you can just take our word for it!

Most Moving Coil cartridges have fairly low voltage output, usually between 0.15mV and 0.4mV. This is why traditional MC-capable phono stages have to make so much gain (55-70dB). They need to boost that tiny voltage up to a standard line-out voltage of 2V. What's interesting about MC cartridges is that although their output voltages are quite low, they tend to output a fair amount of current. A transimpedance phono stage takes advantage of this by essentially ignoring the cartridge's voltage output and instead focusing on the current output of the cartridge.

Voltage and Current in a cartridge have an inversely proportional relationship. Low output cartridges tend to have robust current output and High output cartridges tend to have very little current output. Although voltage isn't necessarily directly correlated with the internal impedance of the cartridge, most higher output cartridges tend towards higher internal impedances. As an example, High Output MC cartridges typically have impedances above 100Ω, Moving Iron cartridges tend to be around ~440Ω and Moving Magnet cartridges are usually 47kΩ.

Once the internal impedance of the cartridge gets over 20Ω there's simply not enough current present on the output of the cartridge to properly drive the current-focused input of a Loco.

Most cartridge manufacturers publish their specs for the internal impedance of their cartridge, but if not, it's fairly easy to reverse-engineer this information. Simply divide the manufacturer's lowest resistive loading recommendation by XXX and that will get you an approximate value!