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Reviewer: Michael Lavorgna
Source: Audio Aero Capitole MKII
Preamp: Déjà Vu Audio, AudioTropic Mœbius [on review]
Amp: Fi 45 Prototype (based on the Fi 2A3 Stereo amp, optimized for the 45 tube by Don Garber)
Speakers: Cain & Cain Abby (Normal) and Cain & Cain Bailey, Tonian Acoustics TL-R2 Super Tweeter
Cables: PHY interconnects, Auditorium 23 Speaker Cable, JPS Labs Digital AC Power Cable, Audience PowerChord, ESP Essence Power Cord, and Z-Cable Heavy Thunder V2 on the Blue Circle MR
Stands: pARTicular Basis rack
Powerline conditioning: Blue Circle Music Ring MR800
Accessories: Symposium Rollerblocks Series II under AA Capitole, Yamamoto Sound Craft PB-10 Ebony Bases under Abbys and Bailey, PS Audio Ultimate Outlets and AudioPrism Quiet Lines. Room damping provided by lots of books.
Room size: 13' w x 14' d x 9' h
Review component retail: $1,500

Open source
DIYers exist in various places on the net, sharing their knowledge and expertise gratis. The fact that some eschew the path to profits of the proprietary approach speaks to a spirit evolved from print magazines like Sound Practices, Glass Audio and Speaker Builder. Discussion forums like DIYAudio, Audio Asylum and AudioCircle now further foster the DIYer tribe. Every so often, a DIYer will spin off and start doing for others as well, venturing into the land of manufacturers or (M)s as they are required to identify themselves in their Asylum profiles. This shift from (A) to (M) can be a full leap into the "opening this unit will void your warranty" type of Microsoftian oligarchy but in some cases, the generous spirit of the DIYer remains intact.

Eric Kingsbury
Macadamia nuts. Well, it was either that or Kona coffee. As it turned out, my review Mœbius
traveled in a chocolate-covered Macadamia nuts box direct from Hawaii. Yes, Hawaii. That's where Eric Kingsbury, AudioTropic's founder, lives and works. (Okay, I'll give you a minute to re-compose and rationalize why it is that we don't all live in a place like Hawaii). "I came to Hawaii in 1967. I was married and my in-laws had come on vacation. They loved it to death to the point that they decided to move there from Lower Michigan. They continued to send back glowing reports until Alice and I decided to follow.

Unfortunately, being in well-off semi retirement themselves, they had neglected to notice that Paradise has the cost of living in Alaska but the median income of Mississippi. I have had a few tough years here, I can tell you. I started making audio gear in the mid seventies. I was a guitar maker by profession and an amateur musician. I lived in a communal hippie house of musicians and we were dissatisfied with the HiFi gear available at that time, especially speakers. It was AR and Rectilinear and Advent and that soft, polite, rounded sound is just not music to a stoned rocker's ears. I had a nice shop so I got Badmaieff/Davis, Cohen, Bernstein and got to work. We didn't have much money so I also got Dyna and Eico kits for the electronic gear. Throughout doing other crafty-type stuff, I've always loved music firstest and mostest and so just kept gravitating back to instruments and gear for reproduction."

Personae. On the boards, we can be whomever we like. We can represent ourselves as faithfully as our egos will allow or transform those warts and lumps into princely pose. The nickname Poindexter used to be much more of a slur before the boom and even that bust hasn't tarnished the promise of practical smarts. Think crafty. Eric Kingsbury is Poindexter on some of the audio boards where he freely discusses all things DIY audio and then some. The only shape shifting I can see is one of convergence. "I have made racing motorcycles, guitars, swords and knives, rifles, hang gliders, airplanes, sailboats and audio gear. Somewhere about twenty years ago, the convergence noticeably took effect."

Convergence. "In this respect, AudioTropic was founded in about 1993. I started using the AudioTropic name about five years ago. It's a double entendre that appeals to me." We can safely assume that there's a lot of Poindexter in AudioTropic and as such, this (M) can be included with the generous-of-spirit clan. This leaves you to freely dig into any level of detail you'd like, about any AudioTropic product right from the AudioTropic website. No searching the web for that scammed schematic, no group of conspirators chipping in to buy and reverse-engineer that prime preamp from the Far East.

From the AudioTropic web site
"... in the spirit of the DIY community, every component that I offer in the products section will be fully explained in the projects pages; if you would like to roll your own, I'll help you as much as I can."

In addition to the Mœbius, AudioTropic offers the Musical Machine [above], an integrated amp based on the 6V6 output tube using the intriguing SILK transformers. On the Projects/DIY side of the house, there's the schematics and further info on our two products as well as a PP EL34 amp, a two-way speaker and a single driver design [left]. I was intrigued by the single driver project but soon realized even my carpenter grandfather would have balked at this one, with its outer/inner kerfing having my thoughts twisted into a pretzel.

The first one-sided surface was discovered by A. F. Möbius (1790-1868) and bears his name: Möbius strip. To obtain a Möbius strip, start with a strip of paper. Twist one end 180° (half turn) and glue the ends together. The first AudioTropic Mœbius was built for Terry Cain of Cain & Cain fame and it was through Terry that I first heard about the Mœbius. Terry's version uses a pair of 6SN7s
whereas the production Mœbius runs a quad of 6AQ5/6005s. For those of you unfamiliar with the 6AQ5 (as I was), it's a small 7-pin beam power tube, the 6005 variant being the JAN/industrial/broadcast grade. Yup, a power tube in our preamp. I asked Poinz about this 6AQ5 choice:

"I like the SRPP circuit. It offers lots of drive device-for-device; low distortion; minimizes the sonic signature of the tube and has pretty good PSRR; ameliorates hum due to ripple on the B+. I had been looking for a robust small-signal tube with a lower gain but then it occurred to me to use a small power tube, of which there are quite a few that are not commonly used. They're pretty much all pentodes and beam tubes but I've been connecting those things up in triode since day one with very good results. I went looking through the usual vendor lists and everybody had lots of 6AQ5s and 6005s at reasonable prices. So I got three or four brands of each to try in a breadboard. It's an interesting device. They all seem to have great big cylindrical plates, are pretty uniform in their characteristics
and sound very clear in this circuit. They're microphonic though, with the JAN 6005 being somewhat better in this respect."

I did some checking around the usual tube suppliers and even the more - shall we say fastidious among them had some prime 6AQ5/6005s from $4 to a high $20 each. As a quick comparison, prime examples of the 6SN7 family can fetch over $300 per pair. The 6AQ5s in the Mœbius should last "at least 20,000 hours" according to AudioTropic's website so you'll have plenty of time to save up for that $20-$80 re-tube.

The SRPP design topology was patented in the US in 1943 and is a simple, elegant circuit operating in push/pull Class A with our 6AQ5s wired in triode. The Mœbius implementation employs zero negative feedback. SRPP in a preamp circuit is not exactly bleeding edge technology. What separates the men from the boys here is convergence; tube & parts choices and the nitty gritty of the implementation adding up to deliver more sonic goods than the cost of your grocery list of ingredients or the simplicity of your circuit would suggest. Think crafty.

"Power rectification is by shunted ultra-fast switching diodes, power supply capacitors are Panasonic TSHA and Nichicon Muse, the power supply is heavily choke-filtered. Signal capacitors are Mundorf Silver Supreme, signal resistors are Riken and Kiwame. Signal wire is high purity copper or silver in Teflon. The chassis rim is cabinet quality exotic hardwood, chassis plates are ⅛” 6061-T6 aluminum, all fasteners are stainless steel."

"This baby has a gain of ~4.5, Z-out (output impedance) of 200Ω, bandwidth (+0, -1dB) of 8Hz to 300KHz (!), and hum+noise low enough to be difficult to measure with a lab millivolt meter, about 0.1mV."

I don't mind letting this cat out of the bag: you can believe that hum+ noise number. This preamp is quiet as in no noise at idle to cozy to my 95dB drivers.

The stock Mœbius has two RCA inputs, a single variable RCA out, a standard IEC power inlet and fuse holder around back. Up front, there are three SwitchCraft silver contact toggle switches and an Alps Blue Velvet volume control. From left to right, the first toggle is the source selector; the second a heater switch or human-powered soft start followed by the power on/off proper. AudioTropic recommends flipping the heater switch and waiting 15 seconds before power-up to extend tube and capacitor life. The review Mœbius arrived with a quad of Sylvania JAN 6005s.