Chances are, you have an opinion about passive line stages, though in terms of “burning questions”, this particular polarizer seems to have dimmed a bit in recent years.
The issue, at least as I can reconstruct a relevant part, is whether or not your typical, traditional, “active” preamplifier was actually doing more harm than good in your current audio system. The wavering finger, the whisper of doubt, all pointed at a potential lack of transparency, and the blame laid (at least in part) at the foot of the pre. A poorly conceived attenuator compounded by a noisy and perhaps unnecessary gains stage, and what you were left with, according to the revolutionaries, was the ultimate forever out of reach.
Me, I’m agnostic about these things.
Morten Sissener, however, is not.
Morten’s company, Tortuga Audio, has just released a rather interesting passive line stage, the LDRx Passive ($1,495). What’s interesting? The light dependent resistors, which many say is the most transparent way to implement an analog volume control. With this latest version of their passive, Tortuga’s LDR array are now fully digitally controlled, and are now fully self-regulating. That’s different. This means that the LDRs are dynamically adjusted to keep them performing optimally, and also has the side benefit of making upgrades and repairs significantly more straightforward. More details on the operation characteristics can be found on the website.
Triode Wire Labs, known at least by me as providing some of the best value in audio cables today, was responsible for all the signal and power connections, featuring their 7awg “Seven Plus” power cords ($499) on the amp PSUs, “American Speaker Cables” ($599/set), “Spirit” interconnects ($349/pair) and the new “Digital American” power cord designed to work with high-sensitivity digital components ($499) feeding the DAC. I’m always happy to point out that all of the cables from TWL are quite robust in the hand but still manage to be almost absurdly flexible and easy to use. That matters. A lot.
The electronics here were from BorderPatrol. The P21 EXD ($12,750), a 300b based push/pull design generates a very still 18wpc. The boxes on the floor are the dual external tube regulated, choke-input filtered, fully mono power supplies.
The BorderPatrol DAC is a bit new. It goes by the rather prosaic name of “The USB DAC” ($975) and has the distinction of being a NOS design. NOS, as in “new old stock” and as in “no over sampling” (and no filtering, either) — the chip is 16-bit only. Yes, there’s the gnashing of teeth, but feel free to put a sock in it. I’ve heard this DAC three different ways and ended up buying it. Why? Because it’s the very best sounding DAC I’ve ever heard. Period. Ka boom. I’m really not sure what the secret sauce is in here, but the TDA1543 chip may well be part. The CM6631A USB transceiver might be part, too, as it dumps I²S directly into the chip. Designer Gary Dews likes to say that the most important part has to do with the power supply feeding it, a low-noise choke-input filtered job with “high-speed rectifiers and RF snubbing techniques to provide a stiff, stable, and noise-free platform from which the DAC can work.” An optional tube regulated, choke-input filtered external power supply is available as an option ($500), but it was not in use while I was in the room. As to “why no high-res”, Gary shrugged and said the new high-res chips simply don’t sound as good. I don’t think he’s opposed to the idea, but whatever, the USB DAC is all about your CD-quality rips.
Last but not least? Yes, the speakers. The Volti Audio Alura A15/MT1 ($15,900/pair) is a 3-way with a 15″ bass driver in a big ol’ bass reflex cabinet that looks a lot like the cabinet he uses for his Extreme Low Frequency subs for his $25k Vittora system. The top cabinet is set upright like a JBL, and features a 2″ mid compression driver and a 1″ compression tweeter waaaay up at the top, both drivers sitting at the base of Tractrix horn. Cabinets are exquisitely veneered Baltic birch and over 1″ thick. The whole thing is made, by hand, in Maine. Specs on the Alura: 99dB, 35Hz-20kHz
The sound in this room was pretty familiar to me, actually, but I will admit that this may well have been the best I’ve heard this speaker sound. The P21 is a thrilling amplifier, and was capable of making the Alura cause spontaneous heart failure for anyone within 50′ of the blast zone. These guys can jump. With the new DAC and Tortuga pre, the sound was about as transparent as I’ve ever heard. Great tone, with horn dynamics and some stunning impact, this was a very interesting system.
