The output stage comprises a 12AX7 gain stage followed by a 6DJ8 output buffer. The circuit has zero global feedback. Tube-rollers can supply their favorite 12AX7s and 6DJ8s, but I evaluated the Romulus with the stock tubes.
The power supply is large and elaborate, with multiple regulated stages for powering different subsections. Even the analog, digital, and clocking sections of the PCM1792 DAC are fed from independently regulated supplies, each with cascaded discrete regulation stages. “Discrete” regulation means that the voltage regulators that maintain a constant DC supply voltage to the circuit are built from separate transistors (along with the peripheral parts that make them work). Discrete regulation is contrasted with IC regulation in which the regulator is simply an inexpensive three-pin integrated circuit. “Cascaded” means that the output of a voltage regulator feeds the input of another regulator, further purifying the DC that powers the audio circuit. Cascaded discrete regulation is expensive and consumes circuit-board real estate, which is why it’s usually only found in mega-priced products.
The input section, along with the Motorola DSP chip on which the filter runs, is powered by a separate power transformer and multiple independently regulated power-supply stages. The front-panel display and control section are also powered from a dedicated transformer. The 12AX7 in the gain stage, as well as the 6DJ8 output buffer, is fed from multiple supplies, including regulated heater supplies.
It’s impossible to overstate the power supply’s sophistication, particularly considering the Romulus’ $7000 price; such implementations are usually reserved for cost-no-object products. I suspect that this approach to the power supply, if not to the circuits themselves, was derived from the development work on Aesthetix’s flagship Io and Callisto. Having designed the best possible products without regard to price, designer Jim White knows exactly what effect power-supply topologies and parts-quality has on the sound, and is able to make the most intelligent trade-offs. Incidentally, White spent many years at Theta Digital before founding Aesthetix.
I should mention that the Romulus is available in a “Signature” edition that features the identical circuit, but with upgraded passive components and isolation feet. The upgraded components include the same expensive capacitors found in the Io and Callisto. When I compared Aesthetix’s Rhea phonostage to the Rhea Signature (whose only difference was passive parts-quality) a few years ago I heard a substantial improvement in the Signature version. The Signature edition costs $10,000 with fixed-level outputs, and $11,000 with variable-level outputs.
From the first CD, the Romulus impressed with its big, open, and expansive sound. It’s interesting how source components can allow a pair of loudspeakers to disappear into the soundstage— or not. Playing a CD that has captured a tremendous sense of space such as Dick Hyman’s Swing is Here on Reference Recordings made it immediately apparent that the Romulus didn’t suffer from the common CD ailments of congealing images and sounding bright without top-octave air. In fact, the Romulus was among the most open and airy digital products I’ve heard—at any price. The soundstage had wonderful dimensionality and depth, coupled with a sense of being “illuminated from within,” a wonderfully evocative phrase coined by Jonathan Valin to describe the classic Audio Research sound. Instruments toward the rear of the soundstage were presented with their tonal colors and spatial qualities fully realized, rather than blending indistinctly into the foreground.
Although the Romulus had tremendous bloom and air, it would be a mistake to interpret this as an artifact of a tubed output stage. On the contrary, image focus was tight and well defined, and the overall perspective was just a bit on the immediate and incisive side—not characteristics of a “tubey” sound. Nothing in the presentation suggested that I was listening to tubes, except the lack of a metallic, brittle character in the treble. The contrast between the up-front midrange presentation and the ability to see way back into the hall produced a soundstage of remarkable depth. The musical benefit was an ability to easily follow individual instrumental lines, no matter how complex the music or how subtle those lines—one of analog’s great strengths, incidentally.