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Synchronicity afforded me a rare opportunity. I could hear Yamamoto's stack over what might be the best single-driver speaker currently in dealerships. Voxativ's stunning 40-20.000Hz Ampeggio is built by the famous Schimmel Pianos plant in Braunschweig/Germany. It's outfitted with designer Inès Adler's hand-crafted AC-3X widebander from Berlin. That unit puts 2.3 Teslas of magnetic field strength into its voice-coil gap, a mere 5.5 grams of moving mass on the scale. The resonant frequency of the driver is a record-breaking 33Hz, Xmax is ±8mm. Voltage efficiency is 98dB. That's ideal for low-powered SET systems.




My first order of business was to compare digital vs. analog attenuation. That's one of the AT-03-1A's very specific intended uses. Sources with variable digital gain for amplifier-direct connection reduce signal strength with software bit decimation. Modern 32-bit chips have plenty of throwaway headroom before digital attenuation eats into real 16-bit RedBook data. The concept has been championed by Wadia for ages. But audiophiles in general are skeptical. They wonder quite understandably how resolution decimation for output voltage trim could really be a good thing.
The Weiss company supports dithered digital attenuation and offers their ATT 202 passive attenuator whose one-source existence would seem to question the superiority of digital-domain manipulation. EJ Sarmento's new USB DAC too offers on-chip attenuation from its 32-bit Sabre DAC. My signal path was Weiss or Wyred4Sound DAC2 (FireWire or USB) off the iMac to passive to J2*. The DACs ran fixed to control volume with the Yammy, then the passive control moved to max to control gain with the converters instead.


The second group of tests leashed the converters in variable mode directly to the amp to properly eliminate the now redundant passive. The detour through the non-attenuating passive in the preceding sessions would determine whether the addition of some quality short wire and connectors was audible. (I did not have a Weiss ATT 202 for inclusion. On paper, it trumps the Yamamoto on modern functionality with its remote-controlled scheme of clutch-powered selector triggering a reed relay resistor matrix; selectable input impedance; and XLR/RCA i/o ports.)
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* For the ultimate in resolution, I initially defaulted to FirstWatt's stunning J2 amplifier. It renders Yamamoto's 300B SET even with the most transparent output bottles by Synergy Hifi or Shuguang Black Treasure comparatively thick, slow and opaque. Expecting potential hairsplitting and the need to hear the tiniest of details from these very fast and translucent widebanders, Nelson Pass' SemiSouth power JFETs were my keenest microscope.
 
For real in-depth analysis, I prefer cuts with high ambiance, complex timbres, LF presence and simple overall structuring. Undue complexity gets confusing at this stage.


I prefer a mix of stringed and blown instruments and light drums recorded pure, then set into a masterful ambient context of the sort Mercan Dede, Cheb i Sabbah and Hector Zazou craft. One of my favorite albums for these purposes is Zazou's In the House of Mirrors. I find it to be maxed out on rich harmonics, long decays and transients of various sharpness. Once I know what to listen for—what areas of differences a particular comparison touches on mostly—I slowly add complexity. For me, the first rounds must be simple and particular however.


One final bit before we go sonic. Passive preamps are a rite of passage just like tubes and ribbons or electrostats. You cannot call yourself an open-minded informed audiophile without having explored the byways of the scene's highways. Active preamps are the establishment, passive preamps—magnetic, resistive or LED—the fringe. Having been there before to eventually settle for 'activated passives' of Esoteric C-03 and Wyred4Sound STP-SE caliber, this assignment became a reunion of sorts. With Yamamoto's direct-heated SET, I'd be in for an unexpected surprise and conditional reassessment.

But first, digital versus analog volume control. Besides affirming that the twice-priced Weiss was superior to the impressive Wyred4Sound in streaming performance, both converters quite upset the defamation league where 'd' stands for digital. The Weiss DAC2 in variable mode offers no numerical confirmation of chosen volume. That's been added since to the far costlier DAC 202 model. The W4S at my chosen playback level showed about 25dB of digital attenuation. This matched the Yammy's own calibration in the analog counter session. With max output voltages for both converters identical, standard listening levels saw them set inside a roughly minus 20-30dB window. Subjective performance offsets between fixed and variable modes also overlapped for both DACs except that the very small difference was more pronounced over the Weiss.


Yes there was an audible difference and no, it wasn't profound by any stretch. The spontaneous term which the Weiss prompted was more insistent. Music in fixed gain mode for the DAC while the Yamamoto handled attenuation sounded a tad more insistent. Timbres felt fleshier/fuller and leading edges more energetic. This degree of difference seemed somewhat relevant upon first switching to this mode but quickly faded as the tracks progressed. It required a high degree of system resolution and listener attention to call analog attenuation superior. Now consider that the Weiss sports four coarse levels of resistive analog gain matching to the chosen amp and its particular input sensitivity. This coarse analog trim will minimize digital attenuation requirements in amp-direct mode. I ran the Weiss in max gain mode to match the Wyred. Chances are that strategic matching to less than 10dB of digital trim would have offered identical performance to fixed output.


What about eliminating the Yamamoto altogether? This became quite the blow to analog supremacists. Going amp direct was superior - more clarity, more immediacy, more energy and transient precision. Why? Hadn't analog seemed slightly superior before when digital attenuation still had to pass through the Yamamoto? Indeed. Yet amp-direct sounded very much like improved drive control; as though the amplifier was much happier coupled to the DACs' output stages than the passive box.


Making this connection an actual explanation—that the DACs' output stages had superior drive and control—is mere assumption. Not debatable was the audible superiority and its flavor which is very adequately encapsulated by the word direct itself. In short, wholesale condemnation of digital attenuation would seem a bit old-fashioned and shortsighted. Perhaps it was true once. It's likely still true if engaged so steeply that resolution decimation crosses the critical threshold.

When implemented as Daniel Weiss and EJ Sarmento have for their respective DAC2s however (and when used within reason and a small window), it not only seems sonically benign but actually advantageous to adopt this type of direct-drive scheme. This does go counter to accepted audiophile lore. And, a system's voicing must clearly be already perfect/complete between source, amp and speakers to make this approach workable and attractive in the first place. Functionally it eliminates analog sources to be minimalist. Without remote control it nearly become hair shirt even. Yet when all the gears mesh without clunks, it actually can make audible and not just monetary or de-clutter sense to eliminate the (pre)amplification stage. I personally would insist on remote volume and a clearly legible numerical display on the variable source then.


Enough now of this detour. If your digital source only sports fixed outputs, you absolutely require a means to control volume. Forget amp direct then. With a single source and deciding between two passives of different technologies, would you prefer Yamamoto's L-pad or Music First's transformer volume control in the above system context?