Sutherland Engineering Phono Block monoblock phono preamplifier
For the well-to-do Porscheophile, the line's ne plus ultra is the GT2 RS ($245,000)the ultimate expression of the Porsche 911 concept and "the fastest and most powerful road-going sports car ever built in the history of Porsche," in the words of Porsche CEO Detlev Von Platen. Every detail of the GT2 RS's design and execution has been stripped down, scrutinized, and optimized, to produce what is, essentially, a civilized racecar for the street. At the top of Sutherland's line is the Phono Block. Though its price of $10,000/pair and general availability make it a bit more obtainable than a GT2 RS, the Phono Block, too, represents a stripped-down, optimized, no-compromise design.
Under the Hood
In keeping with Ron Sutherland's no-compromise philosophy, the Phono Blocks are just that: two completely separate but identical monophonic units. The approach is extreme, but as Sutherland points out, it maximizes separation and eliminates any crosstalk. Each Phono Block chassis externally resembles a Sutherland Hubble, but instead shares its architecture with the 20/20, which I reviewed in the February 2011 Stereophile.
Each Phono Block itself comprises two heavily shielded, individual subchassis, linked by the front and rear panels. The right-hand subchassis is the power supply, which Sutherland says is key to the Block's performance. As in the 20/20, the Block's supplies are AC driven, but according to a much more extreme take on the Sutherland philosophy of putting as much distance as possible between the wall outlet and the audio circuits. Here, the AC is run first through a toroidal transformer, a dual-pi ferrite-bead/film-capacitor filter, and a second toroidal transformer. It then is split into two parallel paths, one for each amplification section of the audio circuit. Each path then runs through a discrete-diode, full-wave bridge rectifier, filter capacitors, a constant-current regulator, and two more RC pi filters. From there, power travels between the power supply and audio chassis via an umbilical nestled in a shielded channel in the front panel, through three more RC pi filters, and a constant-voltage shunt regulator at the load. Even more filtering is supplied in the form of electrolytic and film capacitors bypassing each of the active devices. Sutherland notes that, all told, the power supply has over 100,000µF of capacitance and takes over 20 seconds to charge up when power is applied.
The left-hand subchassis is the audio side, comprising the final power-supply filtering and two gain stages. The first is a low-noise instrumentation amplifier, which acts as an input stage to load the cartridge and supply the initial gain. For the second stage, Sutherland uses an op-amp to accomplish the RIAA equalization and to supply the output current. Rather than use coupling capacitors to eliminate any DC, as he has in some of his other designs, Sutherland wraps both of each Phono Block's amplification stages in a DC servo loop.
It's an oversimplification, but largely true, to say that the Phono Block's audio board resembles that of a 20/20 or Hubble on steroids. For example, the Hubble is itself an extravagant, beautifully executed design, but where it has a 12,000µF bank of thimble-sized electrolytic capacitors, the Phono Block has D-cellsized whoppers totaling over 100,000µF. Everywhere you see a 1µF WIMA polyproylene cap bypassing an active device in the Hubble, in the Phono Block you see both the polypropylene and a pair of 660µF electrolytics. With the Phono Block there's more of everything, everything is bigger, and it's all done to the nth degree. Looking at the audio board, it's obvious why the Phono Blocks are mono unitstwo boards wouldn't fit!
The over-the-top execution applies to the board itself. Sutherland points out that material between the traces on the top and bottom of a circuit board will act as a dielectric, effectively putting an additional capacitor in the circuit. He mitigates this effect by reducing the width of the signal-carrying traces to just 0.015" and having no traces on the underside of the board in signal-carrying regions. Plus, the FR-4 fiberglass circuit board itself is 1/8" thick, which is twice the norm. As Sutherland notes, "I could use exotic materials for the board and get a 10% or 20% reduction in the dielectric effect, but that can cause problems with traces not sticking. By simply using a 1/8"-thick board, I cut any dielectric effects in half. . . . plus, I get easier manufacturability, better durability in the field, and a more stable, rigid platform for the circuit," Sutherland said when I spoke to him about the design.
The Phono Block uses plug-in cards to select loading and gain, which eliminates any switches and puts only a single set of resistors in the circuit at a time. It's an approach typical of Sutherland's design ethos: optimize performance while eschewing any frills or features that might compromise the final sound. "Sure, I could have included a switching circuit to select gain and loading, and had it adjustable with a remote control. I could even have added a digital readout to show what values were selected, but doing any of that would have added complexity and cost, and created noise that I'd have to work to eliminate. At best, the final product would sound no better, and quite likely, it wouldn't sound as good."
The Phono Block does, however, have a couple of features that the other Sutherlands don't. One is a choice of one of three grounding schemes: audio grounding directly to the chassis, floating the audio ground off the chassis, or "soft grounding" through a 50-ohm resistor. Another is the inclusion of a white-noise generator: a small plug-in board that allows the Phono Block to burn itself in quickly and efficiently, or to burn in a set of phono cables. When the burn-in is done, the generator is replaced with the proper loading card and the unit is ready to go. "I'm into adding features that do no sonic damage to the final product," states Sutherland. "When the customer is done with the white-noise generator, they just take it out and there's no harm done."
Use and Listening
Ron Sutherland's strip-down-and-optimize design approach has resulted in the phono-stage equivalent of Porsche's GT2 RS: the Phono Block provides a simple, straight-ahead user-friendliness that no amount of frills and features could approach. At Sutherland's suggestion, I began with the 50-ohm soft-ground setting, plugged in cards for 100 ohms of loading and 60dB of gain to match my Lyra Titan i cartridge, hooked up the Phono Blocks, and I was done. No muss, no fuss, no switches, no adjustments, no remotes, no further choices to make. All that was left to do was to listen.