Bob’s Devices Sky 20-S Step-Up Transformer | REVIEW

bob's devices sky 20-s

What’s better for increasing the gain in your analog set-up, a moving-coil phono stage or a step-up transformer such as the Bob’s Devices Sky 20-S? I’ve heard both sides of the debate and I still haven’t made up my mind. There are a few arguments against SUTs, such as the inductance that comes with iron transformers and the eddy currents created by the signal–I know plenty of people who say they can “hear” transformers and the distortion they can create.

Words and Photos by Marc Phillips

On the other hand, I’ve used SUTs on a number of occasions, and not once was I disappointed with the sonic results. My first experience with a step-up transformer occurred about twenty years ago, when the phono stage in my Yamamoto Sound Craft preamplifier was sounding a bit noisy with my Koetsu Rosewood Standard cartridge–it turned out there was an impedance mismatch and a custom Yamamoto step-up transformer saved the day. Another step-up transformer made a huge impression–the Koetsu SUT I used when I reviewed the Koetsu Urushi Black I reviewed a couple of years ago. That SUT wasn’t optimized for just any cartridge, but it made the already sublime Urushi an epic experience. That combination is still the finest I’ve heard in my own home.

The Bob’s Devices Sky 20-S step-up transformer isn’t the first SUT I’ve used from Bob Sattin. PTA publisher Scot Hull sent me another model from Bob when I first joined the staff back in 2018–it was part of a care package of review gear that got me started on my first issue of The Occasional magazine. I didn’t review it back then since Scot needed it back for one reason or another, but my brief experience with it taught me that these tiny SUTs from Bob’s Devices deliver big sound, and for a reasonable amount of money. (SUTs can be quite expensive, since the coils inside have to be wound so precisely for the ideal results.)

Bob Sattin emailed me a few months ago and asked if I wanted to try his latest step-up transformer design, the Sky 20-S. “I have just developed a new SUT,” he explained. “I call it the SKY 20-S. It is a step up (pun intended) from the old SKY 20. It is still 1:20 and 1:10. Would you be interested in reviewing it? No one (other than me) has seen or heard it.”

I immediately said yes for a couple of reasons. First of all, the MM phono stage of my reference Allnic Audio H-6500 phono preamplifier is so superb that I don’t mind reviewing the occasional MM cartridge–or trying out another SUT with it. Secondly, I had just purchased the Naim NAIT 50 integrated amplifier, which has an inboard MM phono stage. Like the Allnic, the Naim MM phono stage sounds great if you’re still using MM cartridges. But a moving magnet cartridge hasn’t been part of my stable for quite a while, so I knew I had to find a way to pump up the gain so I could enjoy my ZYX Ultimate Airy X and ZYX Bloom 3 carts. The Naim NAIT 50 is so good, it deserves the best I can give it.

step up transformer

Inside the Bob’s Devices Sky 20-S

The Bob’s Devices Sky 20-S ($1,650 USD) is indeed a “step up” from the legendary Sky 20 SUT. As Bob Sattin explains:

“It is heavier and meatier than the SKY 20. It has the same ratios (1:10 in LOW and 1:20 in HIGH).  If your system is very revealing, you will notice the difference. It was hard to upgrade the SKY 20. We tried many combinations and found that by increasing the length of the core, we could change the winding scheme just a bit. You will ‘Hear the Magic.'”

The Bob’s Devices Sky 20-S is tiny, but appropriately heavy due to the transformers. There are two switches on the outside of the Sky 20-S, one that chooses between LOW and HIGH ratios, and another that is marked LIFT and GROUND. Here’s Bob’s explanation:

“Each Bob’s Devices SUT includes a grounding post that can be used to connect your turntable ground and your preamplifier ground. It also includes a ground ‘lift’ switch. In all modes, the transformer cases and faraday shield internal to the transformers are connected to the ground screw. In the ‘GROUND’ mode, the minus or negative side of both output cables are connected to the grounding lug. This configuration works well for those systems where the turntable ground is connected to the negative leads coming from the phono cartridge or where the negative inputs to the preamp are internally connected to ground.

“In the ‘LIFT’ mode, none of the conductors in the RCA jacks are connected to the case, ground, or shield and there is no electrical connection between channels. This design avoids any transformer induced ground loops regardless of the configuration of your other equipment. It can be said that LIFT mode is the same electrically as a balanced configuration.”

Each SUT from Bob’s Devices is hand-made in the US, “one at a time, using point to point wiring and individually tested. No circuit boards are used.”

In addition, Bob included a pair of his interconnects with the SKY 20-S. (A grounding wire is also included–I have tons of those sitting around, but I used Bob’s to preserve his sonic objectives.) Bob’s Devices offers two levels of interconnects–one with a shielded solid silver conductor for $995/pair, and another shielded silver clad copper conductors for $395/pair (which is what I received). These are double-shielded to reduce EFI and RFI.

bob's devices sky


I used the Bob’s Devices Sky 20-S step-up transformer in two very different system configurations. First, I used the Sky 20-S with my reference analog rig–Pear Audio Blue Kid Howard turntable with Cornet2 tonearm, ZYX Ultimate Airy D cartridge and the Allnic Audio H-6500 phono stage.

The second system was a bit of unexpected fun. I hijacked the headphone rig on that bulky oak coffee table in my living room, and I set up an “analog work bench” where I could make quick switches between cartridges, phono stages and cables. I did this for a couple of reasons. First, I was trying to figure out the best way to use my Naim NAIT 50 for vinyl, and so the oak table became the headquarters for making quick evaluations before installation in the main system. Secondly, I’ve been testing out some of the overflow from Scot Hull’s desktop system journey, including such small overachieving transducers as the MonAcoustic SuperMon Mini and Audience ClearAudient 1 + 1 V5 monitors. In other words, the oak table system had become an approximation of a desktop.

The oak table system also became a place to break in components. That brings up a curious thing about the Bob’s Devices Sky 20-S SUT–I’d forgotten that step-up transformers do need a significant break-in period, probably because every time I’ve used an SUT it was such an instant fix for my analog woes. Aside from the time I spent playing with LIFT/GROUND and HIGH/LOW settings to match each cartridge I used, I had to wait for everything to settle in. When first installed, the Sky 20-S sounded rich and meaty, a bit too much in fact, but after a few hours the air and space starts to creep back into the mix and all was right with the world.

Here’s a surprise: after a couple of days, I started to love the sound I was getting from this tabletop system. I thought about my journeyman audiophile years, when I was trying to educate myself about this hobby while living in a series of small apartments surrounded by twitchy, nervous neighbors and overbearing management companies, and setting up my system like this might have taken me further down the high-end audio road than I ever thought possible. Don’t knock near-field listening until you try it.

marc phillips system

Bob’s Devices Sky 20-S Sound

In my main system, the Bob’s Devices Sky 20-S supplied a magnificently black, velvety background to a system that already was black and velvety–thanks to proper grounding from the CAD Ground Control GC1.1 earthing box, and plenty of Furutech NCF products throughout the playback chain. The Sky 20-S was created to accomplish this so it shouldn’t be a surprise, but the performance of the Sky 20-S seemed to single-handedly tip the scales on the SUT vs. active MC phono stage debate. I didn’t hear increased noise and distortion from the iron in the transformers. I heard less noise, something that was easy to discern by switching from SUT to MC.

This set up a showdown of sorts with the Allnic Audio H-6500, which has become my favorite phono pre to use as a reference. Which sounded better, the Bob’s Devices Sky 20-S in the Allnic’s MM input or just the Allnic’s MC input? It took some time before I could readily identify the strengths and weaknesses of both approaches. Over time, I did feel that the Sky 20-S was convincing in the blackness and the silences between the notes, but the MC input of the Allnic was more dynamic and extended in the top. Yes, it quickly became a matter of preference, and I’m sure over a longer period of time I’d use one configuration for one type of music, or I’d prefer certain cartridge match-ups. It’s also worth noting that the Allnic Audio H-6500 costs $9,900, and the Sky 20-S is just $1,650. Plus, you can use them together, which may give you more options when it comes to the rest of the playback chain.

Meanwhile, over on the oak coffee table at the other side of the room, the Bob’s Devices Sky 20-S transformed my Naim NAIT 50 into a powerful little record playing machine. I’d been listening to the Music Hall Stealth for so long with the stock Ortofon 2M Blue, a splendid high-output MM cartridge, that I was shocked when I listened to the Stealth with the ZYX Bloom 3 with the Sky-20. The already mind-boggling soundstage, thanks to the Audience ClairAudient 1 + 1 V5 monitors, stretched out in every conceivable direction. Flipping one switch to GROUND and the other to HIGH, the Sky 20-S suddenly elevated the tabletop system into something less quirky and more faithful to the original musical presentation. Plus, it was easy to really crank the system and get a more visceral thrill from my favorite music.

First of all, the soundstage was elevated and pushed out into the large open space behind the Audiences to the point where this near-field system started sounding closer to what I can achieve with the larger system. Imaging was precise and realistic, low frequencies were smoother and easier to discern (which confirms, for me, that the Sky 20-S is oh-so-quiet). As I mentioned, this system really surpassed my expectations, and adding the Sky 20-S was a final stroke of brilliance.

bob's devices sky

Listening Sessions

The oak coffee table system allowed me to listen to all of the LPs I’ve received in the last year or so. (My primary New Years resolution involves listening more, and putting up with distractions and interruptions less.) There’s plenty of great new music on vinyl in my house right now, and I’ve only listened to a small fraction of it.

If you’re looking for an LP that really captures the essence of blackness in the background and all the rich silences between the notes, however, look no further than Rhymoi Music‘s Three Wishes for a Rose. This is a series of duets between cellist Ma Xinhua and pianist Feng Dan that is enhanced by Rhymoi’s whisper-quiet pressings, and the Bob’s Devices Sky 20-S revealed just how spectacular this introspective and solemn album really is. I found it easy to connect the dots between the two performances, and how each musician was clearly inspired by the presence of the other.

On Robert Vincs’ Chaomorphic, the Sky 20-S made it easier to tell the difference between the saxello, which is a curvier version of the soprano sax, and all the electronic noises that float through the background. This is Vincs’ experimental recording that emulates free jazz while remaining easy and melodic and mesmerizing–this is free jazz that lands in your lap with minimal challenges and no migraines. Chaomorphic is entirely Vincs, with him creating all the magic with just the saxello and an Akai EWI (electronic wind instrument), amid “interactive and generative environments,” so that’s why it’s a master class in presence, decay and proper definition in the transient edges, all while still sounding quite surreal.

I’ve been binging on the Akku Quintet’s Kinema, led by drummer Manuel Pasquinelli, which is full of the type of instrumentals that seem stubborn when it comes to aligning within a genre. Jazz, fusion and math rock join hands and sound simple yet unlike anything I’ve heard. Maja Nydegger’s grand piano really stands out with the Bob’s Devices Sky 20-S in the system–imaging is so precise and yet distant from the listener, but soundstage depth was so amazing that I could clearly “see” the location of the piano–even though it originated from far behind the back wall of my listening room.

One more general observation about the Sky 20-S–it excelled at preserving all the detail at low listening levels. I consider that quality as mandatory for my enjoyment of music because I don’t “crank it” that often, so I usually take it for granted. But with this SUT in the chain, I noticed it right away. In other words, it’s noteworthy if it catches my attention.

marc phillips system

Bob’s Devices Sky 20-S Conclusions

I haven’t really mentioned the price of the Bob’s Devices Sky 20-S since some will balk at paying $1,650 for an audio device so small, and yet those familiar with step-up transformers will know that there are plenty of transformers that cost a lot more. That Koetsu Step-Up transformer, for example, was $5,000 and was much lighter than the Sky 20-S, but it supplied an unbelievable amount of magic to the already mystical Urushi Black. I was also knocked out by the performance of that Phasemation, Yukiseimitsu and Wolf von Langa system at the 2023 Munich show, and Phasemation makes SUTs that run up to $15,000. Making a step-up transformer at this level requires as much focus as making a killer low-output moving coil cartridge.

I’m not sure if any of that matters. The Bob’s Devices Sky 20-S was able to improve the performance of my reference analog rig to a new level, especially in terms of creating a silent platform that allows more music to reach my ears. Plus, it’s made by someone who is uncommonly devoted to the art and science of the SUT, and he’s constantly looking for ways to eke out just a little more realism from recorded music. He’s done that here.

When it comes to the SUT vs active MC phono stages, I’m leaning heavily toward SUTs–especially after my experience with the Sky 20-S. That’s why it earns my highest recommendation.

pta reviewers choice award

bob's devices sky

marc phillips desktop system

marc phillips test bench

music hall stealth


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