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 . . .
The Audio Device
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.
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!
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
Let us pray!
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.
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.
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.
- 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
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.