To set our retro scene of a slower calmer time with the proper atmosphere, let's invoke... yes, Agatha Christie. My favourite episode of David Suchet's immortal Hercule Poirot collection is Cards on the table. The Syrian Shaitana is a very wealthy mysterious Londoner. For dinner and two parties of bridge he invites a group of eight—three professional crime solvers, one crime fiction writer and four people whom he suspects have murdered in the past but gone scot free—with the express purpose of getting himself killed whilst confounding the present quad of sleuths. Before the evening gets underway, the author Ariadne Oliver and Poirot survey their odd assortment of guests with this exchange. "Hm, seems our Mr. Shaitana is a little bit - crime-minded shall we say? He has the most curious taste. One never knows what he's going to find amusing. Might be something - cruel." "You mean, peut-être, like the foxhunting?" "No, I meant something more oriental."

For my less opulent dinner party of four—Dutch Hex, Hong Kong Vega, Korean Eximus, Italian La Scala—the intent was rather more murderous. If it came off, three would lose their lives. Like any good Poirot tale, who'd done it would be the question. But motive wouldn't factor. Audiophiles love shoot-outs that leave just one deck standing. Where our script diverges is that the film's stiletto in the heart was plain from the start. Our 'how' would reveal itself only in stages.
An old timer's mix of coupling transformers, Mosfets and valves.

But first, cards on the table for the Milanese La Scala MkII from designer Cristian Anelli. Only then do we get to grind cerebellum gears over the various score cards of our game and whether the intended audiophile crime of passion (murder by plain superiority) even took place. After all, based on price our spread is tight. In this sector it usually means no decisive best but an array of small differences. At best there's a minor loser but no take-all winner. Yet John Darko's conclusion sowed promise: "There’s no doubt that this is the finest-sounding DAC to date to grace my life/system/website with its presence. Prior to that it was the $4'995 Resonessence Labs Invicta Mirus... Whilst the La Scala MKII is a decoder capable of stunning performance... [there are no] daft PR proclamations that things aren’t as good as they used to be...or that your current DAC sounds ‘broken’." Murder without fanfare perhaps? One obvious distinction for the La Scala MkII are its small triodes. Unlike the norm when this rarer option gets chosen, their bulbs don't couple through capacitors. Aqua use Mosfets. This creates voltage gain in the tube domain, current buffering in solid state. This is similar to what Octave does for their tube preamps. Transistor outputs do lower impedance and increase current to better drive long interconnects. The elimination of coupling caps benefits speed and clarity. A popular rationale for such solutions?

They exploit each device's strong suits whilst avoiding its weaknesses. Hybrid detractors call 'em neither fish nor fowl. They prefer a purist either/or. Here four LEDs per tube act as a constant current source to stabilize its bias current. Two three-legged Mosfets per 12AT7 and a trim pot each cluster in tight proximity for short signal-path circuitry.

At left we show the common 12/7 valve types and their respective gain. For rollers let's also mention each tube's alternate designators including their military 4-digit names. The 12AX7 is also called ECC83, 7025, ECC803, E83CC or 6681. The 12AT7 used in Aqua's circuit is also an ECC81, 6201, 6679 or CV4024. A 12AY7 can go by 6072, a 12AV7 by 5965 and the lowest-gain 12AU7 by ECC82, 5963, 5814 or 6189. Most modern systems suffer from excess gain which explains why this DAC doesn't run with 12AX7. What if you meant to knock down the La Scala's voltage gain a peg or two more, perhaps because you had a high-gain amp like the 35dB Job 225, unusually efficient speakers and in general rather little useful range on your volume control before things got to loud? Without bias adjustments, could a 12AU7/ECC82 be substituted without compromising sound whilst plate resistance drops from 10.9KΩ to 7.7KΩ? "The ECC81 was originally designed for professional high-frequency purposes. Compared to triodes intended for just AF use (audio frequencies), this tube has fast response without roll-off. ECC81 are very linear to exploit low-distortion no-feedback circuits with high input Ω. But everyone knows their output current limits. The Mosfet follower increases current drive so the valve works properly. Tube and Mosfet make a perfect match to deliver nuance with accuracy. And yes, a 12AU7/ECC82 is a drop-in option requiring no circuit adjustments. With a pair of ECC82, one drops the output voltage on RCA to about 1.75V and 3.5V on XLR. "Given the broad choices for ECC81/82 types, rollers could have their little plates full if chasing flavour swings. For many tube fanciers, the inherent freedom to alter a circuit's sound to taste—within limits of course—is one of the attractions. Those keener on turn-key simplicity will stick with the tested and matched specimens Aqua provide. Those are estimated to be good for about 10'000 hours and obviously what the La Scala MkII was voiced around.

(Below right some current Sino, Russian and Slovak specimens plus NOS samples. Price can vary from $10-$150/ea. Popular NOS brands include Amperex, Brimar, GE, Mullard, Philips, RCA, Telefunken and Tungsram. Current production includes electro-harmonix, Genalex Gold, JJ, Psvane and Shuguang. The Euro suppliers EAT, Emission Labs and KR Audio either don't make small-signal tubes at all or just an ECC803S as does Euro Audio Team. Tube Depot valves with boxes at left.)

By the time my loaner arrived, two more reviews had hit. René van Es' for The Ear netted 5 stars. Jürgen Saile's for HifiStatement combined it with the matching La Diva transport. René* assigned different soundstaging qualities to the RCA and XLR outputs. Much depends on your preamp or integrated and how its matching inputs handle the signal. A single-ended preamp for example might use XLR summing op-amps to be the inferior connection; or involve transformers with narrower bandwidth than the direct RCA path. Here assigning firm cause to audible differences can easily mean errors of judgment. Jürgen's review reminded me that of course, only one half of each double triode is used for the RCA outputs. Because the unswitched XLR are live simultaneously, this doesn't 'save' the other half for eventual channel switching and thrifty doubling of life expectancy. Stock bulbs are Russian Genalex. Just then a reader referred me to this Toronto site and owner Alfred Kayser who had supplied me with KR Audio review tubes when I still lived in the US. [Gianmaria Testa's Alta Latitudini and Trumpet Legacy by the Fabrizio Rosso & Flavio Boltro Quintet, recommended by Stefano Jelo.]

* René van Es: "I just read your review of the Aqua La Scala DAC with great interest and was pleasantly surprised that you mentioned my name and refer to the review on The Ear. We both agree, just like Mr. Darko, this is a very fine sounding DAC. However, I did get confused when you mentioned that I heard a difference between the XLR and RCA outputs. So I looked up my review and noticed a true mistake. The word output should have been input. The difference I heard was between the AES/EBU XLR digital input versus the coaxial RCA input. We changed that now in the original article. Apologies for this typo. I caused confusion as I have seen thanks to your comment."

"My friend has a pair of his Brimar 12AX7 running for already 14'000 hours still testing strong. His tubes have been in my amp and preamp for a few thousand hours and perform beautifully. He travels the globe in search of all varieties of tubes. Bar none he is the most knowledgeably guy on tubes I've ever met. He has thousands in stock. Yes, thousands!" To be sure I'd leave no performance under the table, I had to acquire at least one pair of über NOS bulbs to match the top NOS silicon of this deck. If I got just one best-case pair, what would Alfred recommend? Since I wasn't shy on overall system gain, were there sonic advantages to be had by going after 12AU7 instead? Albert had just one answer. "Hands down, the tube to go with is our NOS British-made Mullard 6201 gold pin. It is an absolute reference 12AT7 tube with a dead-black background and superbly musical.

"We have clients using this exact tube in their Neumann microphones for both commercials and singing applications where an absolute black background is critical. In addition and with equal success clients are using them in reference amplifiers and preamps.The only other tube in the world that can rival the Mullard 6201 is the Telefunken ECC801S. Given that the Mullard is less than half the price, it is a total bargain. I also find the Telefunken to be a little more on the cold side. The Mullard will give that DAC a lifelike presence and depth that those crappy Soviet or Chinese tubes could never even imagine." I promptly ordered two pairs for €300 total + $20 for shipping. One of them could go into my Nagra Jazz afterwards, with the other for backup.

Shooting the breeze with the same reader who'd just ordered a second Metrum Hex for his cottage system, I learnt that "one of my clients is a very wealthy gent. He owns an Audio Note DAC 5.x purchased last year. So it's a new model for $50'000 Canadian which has all the options in terms of parts. He was over to my home a couple of weeks ago for wine and cheese. He heard my Hex and was very very upset. It sounded as good to his ears as his Audio Note. So he borrowed it and returned it yesterday. He now has his Audio Note for sale. What is almost as good to my ears? The $850 Resonessence Concero. I have the HD model and run my DSD files through it. It's stunning." This is a reminder. Traffic on the digital highway today is bumper to bumper. Cunningly picked 'mid-level' stuff can be unreasonably close to flagship-priced fare. If you don't compare, you'll be none the wiser. Then ignorance is bliss. If you do compare as we like to, it keeps one honest and less apt to gush over the high-priced spread unless it's really deserved. Time for a wink under the hood. As we already know, the La Scala is laid out fully modular to protect against built-in obsolescence which particularly in this fast-moving sector is a relevant selling proposition.