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Review: Bob’s Audio Devices CineMag SKY 20 Step-up Transformer

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By Darryl Lindberg

There are many ways to skin the audio cat in the quest for sonic bliss. Think about it: if we’re talking about sources, we have vinyl/tape/digital (CD, SACD, streaming, TBD); in electronics we have tubes/solid state/hybrid, as well as single ended/push-pull, throwing in class A/class A/B/D for good measure. If we’re talking about speakers, the choices are breathtaking: dynamic, electrostatic, ribbon, horn, and that’s not even touching on driver composition, enclosure design, bass alignment, active/passive, et al. And then there are the materials themselves: copper/silver/dried otter intestines (just kidding) when it comes to wire. Don’t forget the bewildering plethora of dielectric materials available: teflon/polystyrene/metal foil, et al. Am I boring you yet?

What’s always fascinated me is that, while there may be a theoretical technological advantage to using one approach versus another, it’s always the execution — and the output that’s generated — that counts. And how is that determined? Listening, plain and simple. At least that’s my experience: keep an open mind—and open ears—and you just might find a new audio path to tread. Or … not.

So when it comes to the amplification of the typically puny output of a moving coil cartridge, whether to go active or passive is an executional choice that needs to be addressed. Should the cartridge’s output be stepped up via an active amplification stage or should it be passively amplified via a step-up transformer (SUT)? Not surprisingly, the answer to that question is “it depends”, because there are many examples in either camp that have sonic merit.   And one of them is the item that I’m reviewing: Bob’s Audio Devices SKY 20 step-up transformer. But first a little background . . .

About Bob

So who is Bob and what are his audio devices? Bob is, in fact, Bob Sattin, and yes, he actually builds his audio devices, so you know what you’re getting when you eyeball the logo. Think about that the next time you puzzle over an odd brand name. Anyway, you should know that according to the information-packed website (www.bobsdevices.com), Bob’s not only “built hundreds of moving coil step-up transformers” he’s also “tested more than a dozen of the most popular step up transformers and several step-up pre-amps (head amps) used to match moving coil (MC) Cartridges to phono stage preamps.” Bob’s clearly a step-up transformer animal if there ever was one.

The Audio Device

Sky 20-beauty shotAll of Bob’s Audio Devices SUTs are hand-crafted and feature black powder-coated cast-aluminum enclosures. The RCA jacks and beefy ground connection are gold-plated and appear to be top-quality items. Two high-quality switches take care of gain (high or low) and grounding (ground or lift).

The SKY CineMag series I’m reviewing is distinguished by, according to the website“ultra-high quality laminations, lower inductance and superior sound. These transformers were especially designed and tested with several low-output moving coil cartridges. These are very difficult transformers to construct and require a precision manufacturing process that can only be done by David Geren at CineMag. The same construction techniques are used as in the 1131, except that the inductance of the SKY is even lower due to the lower step up ratios. In addition, the bandwidth is extended a little further.”

Talk about compact! The whole shebang is only 4 ¾” x 3” x2 ¼” (LxWxH, including the protrusions of the switches and jacks) and weighs a mere 9.8 ounces. However, it’s packed with everything you need for amplifying your moving coil’s output to a usable level. My editor sent me two versions of the SKY CineMag: one higher gain (SKY 30) and one lower (SKY 20). The SKY 30 is switchable for 1:15 (24 dB gain) or 1:30 (30 dB gain); the SKY 20 is switchable for 1:10 (20dB) or 1:20 (26dB).

My Jadis JP200 MC preamp’s a full function rig with moving coil and moving magnet inputs, which means that the step-up transformer is connected to the moving magnet input. Because the JP200’s MM input has a very high specified gain (59dB), I used the SKY 20 with the gain switch at “low”. Too much of anything is usually not recommended and that includes gain. I also found the lowest noise with the ground not lifted and the grounding leads from the Rockport and SME V attached to the SKY 20’s grounding lug.

How does it work? Through the magic of electromagnetic induction, a step-up transformer increases the miniscule voltage output of the cartridge to a level that will be acceptable to the sensitivity of your (moving magnet) phono input. More specifically, a step-up transformer is composed of two coils of wire wound about a multi-layered frame (usually iron or some alloy thereof). The coil winding that’s connected to the output of the cartridge is the primary; the coil that’s connected to the phono stage is the secondary. This secondary coil will have a greater number of winding turns than the primary; the ratio between the primary and secondary windings is called, naturally enough, “the turns ratio”. The turns ratio determines the how much the cartridge’s voltage is stepped up. Bob provides a handy information card that indicates the amount of step-up (in dB) for a given turns ratio and impedance (in ohms). In the case of the SKY 20, it’s 26 dB/118 ohms (switch set high) and 20 dB/470 ohms (switch set low).   It’s important to remember that a step up transformer only amplifies the cartridge’s voltage; RIAA equalization must be provided by the phono input of whatever device you’re using to provide accurate playback.

What’s the advantage of using a step-up transformer? For one thing, it’s a straightforward, passive device that’s powered by your cartridge: no capacitors, resistors, regulators, transistors, or tubes to be found. For another—probably as a result of its passive nature—transformers can be much quieter than active circuits.

Naturally, since nothing in audio—or life, for that matter—is perfect, a step-up transformer can have downsides. For example, a SUT can potentially restrict dynamics and/or limit frequency response. There’s also the fact that a SUT requires another set of interconnects, which means that there’s another break in the signal path. Given the demise of the full-function preamp and the rise of the separate phono preamp, the extra connections are typically a fact of life, so maybe it’s not that big a deal.

But it’s possible to minimize some of the downsides of a SUT. Like everything else in audio, the sonic devil is in the details. As I said up front, it’s the execution that matters. Even though a transformer appears to be conceptually simple, transformer manufacturing is actually an artisan business. Winding transformers is an art; it’s not just insuring that the turns ratio is correct. It’s the tensioning of the wire, the type of wire, the core upon which the wire is wound, and many other factors that I’m sure I’m missing. The fact is that a well-designed step-up transformer can be just as effective (or even more effective) at amplifying a cartridge’s output as an active device.

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On with the Show 

I used the SKY 20 with my go-to Air Tight Supreme (.4 mV) along with a good smattering of the Allaerts MC-1B Mk.2 (.65 mV), and a bit of an Ikeda 9CIII (.17 mV). The rest of my system hasn’t changed much over the past year: Rockport II Sirius SE and highly-modified V.P.I. HW-19/SME-V turntables; electronics were the Jadis JA200 amps and JP200 MC preamp; speakers were my ever-faithful Avalon Eidolons (see associated equipment for the rest of the set up). Just so we’re clear: the SKY 20 was connected to the JP200’s moving magnet input, so any comparisons I make are to the same cartridge into JP200’s moving coil input. It’s really quite simple. I don’t have another preamp on hand, so that’s the way it is.

Let’s get down to listening . . .

Really detailed notes—just in case you have questions!

BobsDevices-1204I wanted to start out with some edgy, modern music with limited instrumentation, so I began with George Rochberg’s String Quartet #3 (Nonesuch H-71283), performed by the Concord String Quartet, recorded by the great Marc Aubort/Joanna Nickrenz duo, and mastered by Bob Ludwig.   For those of you who, like I, lurked in the Cretaceous vinyl period, you’ll remember that Nonesuch was a budget label that released a very wide variety of music, some of it important and not recorded by the “full price” labels, some of it eminently forgettable, but all of it worth the pittance charged. Ah, if only today’s budget labels were as fastidious and adventurous—wait, are there budget labels today? Moving right along . . .

The recording is close-up and honest: you get the sense that the quartet is playing right in front of you. Another way of putting it is that you don’t get the impression that you’re in a concert hall; instead, you get the impression that the Concord String Quartet’s playing in your room. And here’s what I like about the SKY 20: it lets you know you’re listening to an excellent recording. It may seem obvious, but some gear obscures the attributes of a good recording to the point that it’s no longer involving. But not the SKY 20: it doesn’t editorialize or leave some of the information back on the vinyl.

That doesn’t mean there’s not a difference between the JP200’s moving coil input and that of the SKY 20 (Air Tight PC-1 Supreme) through the preamp’s MM input. I would have been gobsmacked if there wasn’t.   Although the difference wasn’t of the order of magnitude variety, it was readily apparent. Compared to the MC input, I got a little less “there-ness” and a bit of soundstage flattening. However, there was no doubt that the SKY 20 was faithful to the input. It’s a slightly different, pared down presentation compared to the MC input, but that’s not against the law here.

This difference between the MC input and SKY 20 was magnified when I strapped on the Ikeda 9, possibly because the Ikeda’s a really low output MC. It’s also a cartridge that’s much lower-end than the Supreme and definitely not as refined. This difference was more apparent through the JP200’s MC input. Again, it was noticeable, but not that big a deal.

The first—and probably last—recording

BobsDevices-1205Next up was an LP that I got for one thin dime: Donald York’s compositions for the Paul Taylor Dance Company (Music Masters MM 20064). I was going to pass it by, but then the usual manifestation of the “acquisitive Darryl” doppelgänger forced me to fork over the dough. Even though the music’s derivative Copland-esque Americana, it’s enjoyable and eminently suited for its intended purpose: dance. And the recording is thoroughly excellent. The SKY 20 reproduced the vividness, for lack of a better word, that distinguishes this recording. Again, the SKY 20’s presentation through the JP200’s MM input differed from the straight-in MC input, evident in a slightly constricted stage width and just a bit of flattening. For example, the trumpet on the “Diggity” piece is not as far back or as far to the right as it is through the MC input. If I weren’t comparing, though, I’d be pretty well satisfied with the SKY 20’s presentation.

Let us pray!

BobsDevices-1207It’s hard to beat a good vocal recording to test out a piece of gear. But I’m not going to sport with your patience by trotting out yet more Diana Krall, Patricia Barber, or the plethora of other “audiophile approved” chestnuts. Instead, I put on Beethoven’s initial foray into “mass music”, his Mass in C (Argo ZRG 739). This LP is a typically excellent Argo effort, performance-wise and sound-wise (not surprising, given that Kenneth Wilkinson and Michael Mailes are credited with the engineering). Here’s a disc that’s still fairly easy to find and not stratospherically priced on the used market. Best of all, it features a fine performance of great music, featuring an all-star vocal line-up of Felicity Palmer, Helen Watts, Robert Tear, Christopher Keyte, and the Choir of St. John’s College, backed up by the Academy of St. Martin-in-the-Fields, with George Guest at the podium.

Once again, the SKY 20 lets you know that you’re listening to, in this case, a very well-recorded LP. As I said before, there are differences versus the JP200’s moving coil input. On this recording, the bass had less oomph and extension through the SKY 20. However, the atmosphere of the concert hall and the placement and realism of the singers/chorus was reproduced in abundance.

The young goddess high-five.

BobsDevices-1208Finally, I put on Ernest Ansermet’s take on Debussy’s Images (London CS 6225; “narrow band”). The dynamics on this record can be startling and SKY 20 did them justice. The bass reproduction on the last movement, Ronde de Printemps was articulate, but not overemphasized. And the SKY 20 really strutted on the Stravinsky piece on side two, Symphonies for Wind Instruments, a variable feast of reeds and brass tonalities. As you might expect, the MC input produced a bit more color, depth and bass on Images and more brassy “blat” on the Stravinsky, but the SKY 20’s presentation sure wasn’t anything to sniff at.

Almost the End

I’ve read a lot of reviews over the years and I know that one of the standard catch-phrases is that “the difference was not subtle”, or words to that effect. But I’m not going to go the pretentious reviewer route on you; you know, the “I’m blessed with acute sensitivity, taste, and a massive level of exposure you’ll never have” attitude. The fact is that in the case of the SKY 20, the differences versus the JP200’s MC input were certainly apparent; however, these differences, for the most part were subtle. Remember that I’m comparing the SKY 20 to what’s essentially an all-out, totally dual mono, mucho gonzo phono preamp—that happens to reside in an all-out mucho gonzo line stage.

Compared with that absolute reference, the SKY 20 acquitted itself admirably.

The End

I really liked the SKY 20—it was impossible not to like it. For a relatively reasonable outlay of the old skrilla ($1,250), you get a very well made SUT that should satisfy even the most discriminating vinyl-o-phile.

My only word of caution—and this is in no way a criticism—is to be vigilant if you use gargantuan interconnect cables or you may find the diminutive SKY 20 appropriately named and heading off into the wild blue yonder.

Associated Equipment

  • Pre-amp: Jadis JP200 MC
  • Amplifiers: Jadis JA200
  • Speakers: Avalon Eidolon
  • Turntables: Rockport II Sirius LE, VPI HW-19 Mk.IV (various upgrades)
  • Arms: Rockport (integrated with turntable), SME V
  • Cartridges: Air Tight PC-1 Supreme, Allaerts MC-1B Mk.II, Ikeda 9CIII
  • CD Transport: Mark Levinson 31.5
  • Digital Processor: Mark Levinson 30.6
  • Speaker cables: MIT 850 EVO
  • Interconnects (all single ended)
    • Preamp-amps: Purist Audio 25th Anniversary Luminist
    • Turntable-preamp: Custom, one-off MIT (Rockport); Kimber KC-TG (VPI)
    • DAC-Preamp: Acoustic Zen Silver Reference
  • Power Cords: Jena Laboratories Two
  • Equipment rack: Ginko Platforma (Cloud 10 platforms for preamps)
  • Amp stands: Target

About the Author

IMG_0629Darryl is a retired executive living in Santa Fe, New Mexico. Although he gets a good deal of exposure to live music via season subscriptions to Santa Fe’s various opera, orchestral, and chamber music groups, Darryl believes a great sound system is the only practical means invented by modern technology to experience the work of long gone (i.e., sleeping with the fishes) or simply inaccessible artists and their performances—at least in his current temporal existence.  And he has plenty of software to stimulate his auditory contemplations, given that he’s amassed and continually adding to a vinyl collection of well over 10,000 records.

Audio being a hobby (this is the Part-Time Audiophile, right?), Darryl spends much of his non-listening time volunteering for various worthy—depending on your point of view—organizations.  In addition, he hosts a weekly program, “Tuesday Night at the Opera,” on Santa Fe’s public radio station, KSFR (7:00-10:00p.m. Mountain Time; streaming live on www.ksfr.org). Further background may be obtained from his parole officer.

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