Listening #171: Bob's Devices Sky 40 transformer Page 2

Arguably more important, the Sky 40 delivered as much impact, drama, and overall involvement as the more expensive Hommage, so much so that I felt compelled to listen to the album all over again, beginning to end. By the end of "Love You To," I caught myself playing air tabla on my desktop (it seems the Sky 40 also allowed the music its fullest sense of drive), and I enjoyed, among other delights, the enhanced realism of the sound of Ringo's drum entrance—a ride-tom beat followed by a floor-tom beat—in "Here, There and Everywhere." (And, yes, as my dog could probably tell you, it was one of those listening moments when I also caught myself uttering, to the otherwise empty room, such erudite outbursts as "Holy shit" and "Wow.")

From there I proceeded to the Hungarian String Quartet's 1966 recording of Beethoven's Quartet 14 in c-sharp, Op.131 (Seraphim SID-6007). The Sky 40 did a first-rate job of reproducing the unornamented, fugue-like first movement (Adagio) with both clarity and texture, and with a fine and ultimately thrilling sense of momentum. The brisker, sunnier fifth movement (Presto) was no less well served, pizzicato notes popping out as they should, while the sixth (Adagio) and seventh (Allegro) movements came across with texture, color, drama, and drive—all as well as I've heard from this record. (That said, I really wouldn't mind hearing an EMI original some day!)

And like all my favorite audio products, the Sky 40 allowed music to sound vivid. The massed violins in Stanislaw Skrowaczewski and the Minneapolis Symphony's recording of Schubert's Symphony 8 (Mercury Living Presence SR90218) comprised a honeyed, colorful, physically huge force that I couldn't have ignored if I'd wanted to. The massed voices and vibraphone in the first part of Britten's Spring Symphony, in the recording made by the composer, vocal soloists, and the orchestra and chorus of the Royal Opera House, Covent Garden (Decca SXL 2264), came through with vibrant colors, and the Sky 40 seemed to highlight the dynamic interplay between soloists and chorus in the third part. Even the sound of that second-most-common of all instruments, the piano, became almost exotic in its vivid, colorful presence in the Melos Ensemble's recording of Schoenberg's Suite, Op.29 (L'Oiseau-Lyre SOL 282).

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The Sky 40 was also an impact champ. Dave Mattacks's drums in "Tam Lin," from Fairport Convention's Liege & Lief (Island ILPS 9115), though compressed in the original recording and more than a little dull, had never sounded so forceful as they did through the new trannie. And in that album's hauntingly beautiful final number, "Crazy Man Michael," the sound of Richard Thompson's electric guitar, played through a Leslie rotating speaker—which itself compresses the signal before it even arrives at the mixing desk—had some of its touch restored on its trip through the Sky 40. The sound of Neil Young's shambolic live album Time Fades Away (Reprise MS 2151) also gained in apparent realism. Apart from Johnny Barbata's kick drum, whose sound is small and oddly disconnected from the sound of the rest of his kit, the instrumental sounds on this record have a fine, raw sense of force, and the Sky 40 enhanced those qualities.

At first, I tended to think of the Sky 40 as a forward-sounding device, but it turned out to be both more and less than that: In even the subtlest recordings, it found those elements that should be pushed to the front of the stage, so to speak, and did so. In that sense, the Sky 40 had spatial nuance in a manner that escapes lesser transformers—spatial nuance allied with dynamic nuance. I thought of this as I listened to the opening bars of Charles Munch and the Boston Symphony Orchestra's recording of Debussy's La Mer (RCA Living Stereo LSC-2111) and heard, clearly, the differently timed chords played by the two harps—and how, as the piece progressed, the two harp parts diverged and then recombined. If a transformer can let me be grabbed by Debussy, it can do anything.

Mono a mano
Before returning my sample of the Bob's Devices Sky 40, I wanted to try it with something other than my Shindo SPU, brilliant thought that match-up was. The nearest cartridge to hand was my EMT ODF 15 true mono pickup head (footnote 5), which outputs 5.75mV and has an internal resistance of 37 ohms—on paper, a terrible pairing! But, as many before me have experienced, there's something about the Hommage T1 transformer, which has the same apparent gain as the Sky 40 and which I presume to have a primary coil of similarly low impedance, that allows it to sound downright brilliant with every high-output mono EMT I've thrown at it.

So I tried it, all the while making sure to reduce the gain of my power amplifiers, in order to let the preamplifier's volume knob function within a reasonable portion of its range (which I also do when using the Hommage T1 with the EMT OFD 15 and the identically specced OFD 25). And here, the sounds of the Hommage and the Sky finally diverged, albeit not by a great deal.

As anyone with an ounce of engineering smarts will tell us, using a 37 ohm pickup to drive a transformer with a ca 5 ohm (presumed) primary coil should not work—and yet it did. Listening to my current favorite recording of Schubert's Piano Quintet in A, D.667, "Trout," by pianist Jörg Demus and the Schubert Quartet (Deutsche Grammophon LPEM 19 206), I was stunned by the way the Sky 40 endowed all of the stringed instruments, especially the cello, with a palpable sense of body. Musical momentum, too, was thrillingly good, as was also true when I listened to the Cappella Russian Male Chorus, conducted by Nicholas Afonsky, perform a Russian Orthodox Requiem—a sometimes frightening recording that exhales mystery with every note (Westminster XWN 18263). And when I turned to my old standby "Chelsea Bridge," from Gerry Mulligan Meets Ben Webster (Verve MGV-8343), I was pleased to hear the same presence and touch I hear through the Hommage—but not nearly all the bottom-end whomp I hear through the Hommage when, after the first chorus, bassist Leroy Vinnegar switches from bowing to plucking his instrument.

That's no criticism of the Sky 40—which shouldn't work at all in this setting. (Short of sawing an Hommage in two to crack the secrets at its core, I doubt that anyone other than designer Keith Aschenbrenner will ever know why it works as crazy-well as it does.) The point seeming to be: If you own various different cartridges and/or pickup heads and you want to limit yourself to owning just a single step-up transformer, you might want to choose one that suits the lowest-output, lowest-impedance cartridge in your collection, because that transformer is likelier to also give satisfactory results with your higher-output cartridges than the other way around. (Although it's been a while since I tried using a low-output cartridge with a low-gain transformer, my experience suggests that the results are often musically dead and sonically dull.) Your higher-output cartridges may sound a bit too boisterous with that high-gain trannie, but it's easier to make up for that than to restore momentum and drama and impact that have gone missing.

The grander point, of course, is this: If you own an Ortofon SPU or similar low-output MC cartridge and you're looking for a giant-slayer of a step-up transformer, this may be the product you've been waiting for. The Bob's Devices Sky 40 won't make serious phonophiles forget all about the Hommage T1—or the Audio Note AN-S8, or the Western Electric 618B, or any of the other transformers that might lay claim to the title The Best—but it will give hobbyists of less-than-extravagant means a chance to wring even more enjoyment from their favorite records.



Footnote 5: Like EMT's OFD 25 and OFD 65, the OFD 15 contains only a single coil: although it has four output pins, signal appears on only the two right-channel pins, requiring a right-to-left jumper at the preamp stage.
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COMMENTS
GLADYS ZYBYSKO's picture

They NEVER come up into the hills!

jimsusky's picture

I wholly agree that a well-designed SUT is a fabulous - even cost-effective way to amplify lo-output moving-coil pickups. Two plausible reasons:

1) Lo-output coils have a supersonic high end - due to low coil inductance.
2) Moving coil transformers, being entirely passive, contribute zero noise.

Add to this the practical benefit that an SUT allows virtually the entire world of phono-preamps to be used - with a little attention paid to the preamp's overload margin. I believe it is a much simpler design challenge to hold noise down with less gain required for the active preamp.

I well-remember the "L-strapped Cotter Brick" (MK-2L) which offered 37db voltage gain. That worked very nicely with the various lo-output Ortofon, Fidelity Research, and Accuphase pickups of 1981-1986 or so.

Kudos to Art Dudley for giving the simple voltage gain to db gain relation. but I'm not sure where Art got the:

ca 5 ohm (presumed) primary coil figure.

A 40:1 transformer will "transform" the input impedance of the phono preamp using a squared-law relation. In this case, for a 47k-ohm input impedance:

Impedance "seen" by the pickup = (47,000)/[(40)(40)] = 47,000/1,600 = 29.4 ohms.

Round it up to 30 ohms.

Perhaps Art meant the DC impedance of the primary coil is 5 ohms. Perhaps the manufacturer will weigh in.

(I'm not so sure using an ohm-meter with a 9-volt battery is advisable to check this)

Anyway, terrific review.

(considering inflation, $1200 is quite reasonable compared to the $600 the Cotter cost ca. 1979-1981.)

jeffdyer's picture

"Because, with exceptions, transformers offer better sound—providing more drama, more color, and, especially, greater touch and impact."

So, less fidelity. Hmmmm.