The main benefit of an external power supply is to keep an audio product’s power-generating circuits well away from the circuits that handle the delicate audio signals. In theory, this should reduce noise. Nonetheless, I don’t believe I’ve ever reviewed so highly specialized a product as Simaudio’s Moon Evolution 820S power supply ($8000 USD). On its own, the 820S does nothing; instead, it’s an external power supply intended for use with these Simaudio Moon Evolution models: 740P preamplifier, 650D and 750D transport-DACs (the latter is now discontinued), 780D streaming DAC, and 610LP and 810LP phono stages. The 820S bypasses and replaces only those products’ built-in power supplies. However, a single 820S can be used to power one or two of those models. That’s important -- if you use it with two, its rather high price becomes easier to justify (see below).

Moon by Simaudio Evolution 820S

Another benefit claimed by Simaudio is that the 820S’s circuit design and parts are slightly better at reducing noise and providing stable voltage than those comprising the power supplies of the components it’s compatible with. I have the Moon Evolution 650D transport-DAC and 740P preamp, which I respectively reviewed in 2012 and 2013. Today, those models retail for $9000 each. My goal with the 820S, which was launched in 2015, was to see what kind of improvement, if any, it could work on their sounds -- on their own, the 650D and 740P already sound so good that it’s hard to imagine them sounding any better.


Most high-quality, standalone power supplies I’ve seen are designed to be placed alongside or behind an equipment rack, and so have no-frills cases to help keep cost down. But with the 820S, Simaudio has taken the costliest approach by building it to match the Moon Evolution models it’s to be used with. It shares their style and dimensions -- 18.5”W x 4.25”H x 15.5”D -- has the same truncated-cone feet, and is built of the same materials to the same standard of quality: heatsinks running along the sides; a super-thick, tiered top plate capped with the Moon logo engraved on a silver medallion; and a front panel with thick, curved “cheeks” that flank a flat, 9.5”W central section of 3/8”-thick metal. And the same finish options are available: black cheeks and centerplate, silver cheeks and centerplate, black cheeks and silver centerplate, or silver cheeks and black centerplate (other, custom finishes are available at extra cost). My review sample’s black center plate and silver cheeks matched those of my 650D and 740P.

Besides the 820S looking like other Moon Evolution models, another benefit of uniform cases is that they can be stacked, to save space and make for a tidier appearance. I stacked them -- 820S on the bottom, 740P in the middle, 650D on top -- by setting the feet of one case atop the corner posts of the case below it. That works well, but anyone who owns two or more Moon Evolution models should seriously consider Simaudio’s Moon Bridge aluminum couplers ($500/four). These have elastomer pads on the bottom that rest on the component below, to prevent scratches and reduce the transfer of vibrations between components.

Moon by Simaudio 820S

The 820S is actually two power supplies: one to feed the analog circuits of a component hooked up to it, the other for the digital circuits. In this case, analog circuits refers to the electronics that the audio signal passes through; the digital circuits are those of a transport mechanism, front-panel display, controller board, etc. Simaudio explains:

The analog and digital power supplies each have 2 special “pi-type” filters after the initial voltage rectification stage that reduce AC transmission noise, using 40,000µF of capacitance (4 x 10,000µF) and dual choke inductance (2 x 20mH).

The analog and digital supplies each have 4 stages of our proprietary M-R2S circuit; A fully discrete voltage regulation circuit using a “precision reference” feeding an amplifier made up of numerous IC’s and transistors, as opposed to a single voltage regulation chip. M-R2S outputs pure DC power that is exceptionally fast, very precise, has a virtually unmeasureable noise level, as well as absolute stable voltage.

Simaudio claims that noise from the 820S is further reduced by the use of four-layer circuit boards “with pure copper tracings and extremely low impedance characteristics yielding much shorter signal paths and drastically reduced noise levels.”

Moon by Simaudio 820S

Compared to the 650D’s and 740P’s front panels, the 820S’s faceplate is spare, bearing only the silkscreened model name on the left, the Moon logo toward the top in the middle, a single Standby pushbutton toward the bottom middle, and, above that and below the logo, an LED that glows blue when the 820S is fully operational, after Standby has been pressed.

The rear panel is also less cluttered than the 650D’s or 740’s: just an IEC-compatible power-cord inlet and a main power switch beside it, and two pairs of XLR connectors, marked Output 1 and Output 2, respectively for the analog and digital DC-power outputs. Four proprietary XLR-terminated cables are supplied to use with these connectors. These cables are specially made to deliver only DC power; they can’t be used for line-level audio signals, nor can standard XLR-terminated interconnects be used in their place.

Moon by Simaudio 820S

Connecting the 820S to a component(s) is simple: On the rear panel of a compatible Simaudio model are connectors for Input 1 and Input 2. Just run one XLR power cord from one of the 820S’s Output 1 connectors to the other component’s Input 1, then do the same from one of the 820S’s Output 2 connectors to the other component’s Input 2. If you have a second compatible component you want to power with the 820S, do the same with the remaining Output and Input connectors. Now, as only the 820S needs to be plugged into the wall, remove the power cords from the component(s) connected to the supply. For power up, the 820S’s main power switch must first be turned on, after which it can then be left on all the time, to keep the supply’s circuits warm and running optimally. (My review sample has been off only twice in the many months I’ve had it.) Then, for daily use, the 820S’s Standby button must first be pressed to power it on; only then can each connected component be turned on, by pressing its own Standby button.


When I reviewed the Moon Evolution 650D DAC-transport, in 2012, what I liked most about it was that, as I then said, it provided “the most musical and nonfatiguing sound I’ve heard from any digital source.” Since then, I’ve heard DACs I’ve liked better -- e.g., the EMM Labs DAC2X ($15,500) and the Hegel Music Systems HD30 ($4800) -- but sonically, the 650D is still no slouch, and even after four years it hasn’t been substantially outclassed. When I reviewed the Moon Evolution 740P preamplifier, in 2013, I described it as “a benchmark for preamplifier performance for under ten grand -- not for what it sounds like, but because it sounds like nothing at all.” I still say the same today -- I haven’t found any other preamp at or near its price with the same level of transparency to the signals it passes along. Because each of these components sets a high standard on its own, I would have been very surprised had the sound of either been greatly improved by being powered with a Moon Evolution 820S.

Moon by Simaudio 820S

Well, I wasn’t surprised. With the 740P still plugged directly into the Shunyata Research Venom PS8 power distributor I normally use for my electronics, and with only the 650D connected to the 820S -- also plugged into the Venom PS8 for the duration of my listening for this review -- I played a random selection of music fed from my laptop computer. (I no longer use the 650D’s CD transport because all of my CDs are now ripped to a hard drive.) Right off the bat, I heard a subtle improvement in image focus -- that is, how sharply outlined the aural images of performers are on the soundstage -- as well as a bigger soundstage (though how much the stage grew depended on the recording played). I thought the 650D also sounded a bit more dynamic, which was welcome -- one of my reservations about the 650D has been that its sound is a bit too laid-back. These weren’t drastic improvements, but when I heard them, I surmised that the 820S had lowered the 650D’s noise floor (i.e., how much self-noise it produces) a little bit. However, when I reversed this setup by connecting the 740P to the 820S and plugging the 650D directly into the Venom PS8 distributor, I struggled to hear similar improvements. It didn’t sound worse, but I couldn’t be certain that the imaging or soundstaging had improved, and I heard nothing else that sounded better; it wasn’t clear that the 820S was doing anything I could hear. It seemed clear that the 650D benefited more than the 740P from being powered by the 820S.

Next, I played only recordings that I know extremely well, and that capture a great deal of soundstage information. These listening sessions were much more revealing of what the 820S could do. For example, in “Misguided Angel,” from the Cowboy Junkies’ The Trinity Session (16-bit/44.1kHz FLAC, RCA), the soundstage is cavernous and the musical images are precise. With only the 650D connected to the 820S and the 740P plugged into the Shunyata distributor, I heard the same improvement in image focus that I had with the other recordings, but this time the soundstage seemed even wider, which made the recording venue -- the sanctuary of a large church -- seem even larger. After swapping the components again, so that the 740P was now connected to the 820S and the 650D to the distributor, I could hear an increase in soundstage space, though not as much as I’d heard when the 650D was powered by the 820S -- the room sounded bigger, just not quite as big. With the 740P plus 820S, image focus was about the same as without the 820S; what I could now hear more of was the air around the musicians, which made for a more believable illusion of real musicians playing on a real stage.

Moon by Simaudio 820S

The next step was obvious: connect the 650D and 740P to the 820S. When I did, the soundstage was slightly bigger than when just one was powered by the 820S, and this held true not only for The Trinity Session but also for the orchestral score for the film The Mission (16/44.1 FLAC, Virgin), a recording I’ve used as a reference in dozens of reviews -- the better the gear, the bigger its stage seems to get. Image focus also improved with both the 650D and 740P plugged into the 820S vs. what I’d heard with just the 650D powered by the 820S. For example, in track 3 of The Mission, “Gabriel’s Oboe,” the timpani, which sound like they’re coming from 60’ back, were presented with laser-pointer precision in terms of their depth and positions on the stage. Furthermore, individual choristers’ voices were placed so precisely on the stage that it seemed I could actually see who was singing.

This improvement in imaging was also obvious with “Everest,” from Ani DiFranco’s Up Up Up Up Up Up (16/44.1 FLAC, Righteous Babe). In this recording, DiFranco’s voice and guitar are deliberately -- not to mention oddly -- mixed to appear in the left part of the stage. Often, when I play this track, people think there’s a problem with the system’s channel balance, but there isn’t -- it’s the recording. With the 820S in the chain, DiFranco’s voice and instrument were spotlit on the stage as precisely as I’ve heard, surrounded by a tight cloud of “musical air” that hovered around her such that I could imagine the small space she was recorded in.

Moon by Simaudio 820S

Once these recordings had given me a handle on what sort of improvements to listen for, I then played tracks on which, I knew, soundstage information had not been captured that well -- mostly, recordings of pop music in which any semblance of a soundstage has been created on a mixing board. Given that improvements were most noticeable when both the 650D and 740P were connected to the 820S, I left my system set up that way. When I focused on Sade Adu’s voice in “Long Hard Road,” from Sade’s Soldier of Love (16/44.1 FLAC, Epic), I thought I could hear a better delineation of her voice from the backing band, but the difference was small enough that most would consider it inconsequential. It was the same with Adele’s voice in “Rolling in the Deep,” from her 21 (16/44.1 FLAC, XL Recordings): any improvement in soundstage space, image focus, or delineation from the other instruments was pretty much impossible to be sure of. With Adam Cohen’s We Go Home (16/44.1 FLAC, Resolute Music), I did hear improvements in soundstage space, image focus, and air around instruments, particularly in “Song of Me and You.” This I chalked up to the recording having been of acoustic instruments played in a typical living room (from what I understand, Cohen recorded the album in the houses he grew up in in Canada and Greece) with what sounds like very little postprocessing. Production-wise, We Go Home is closer to The Trinity Session than to Soldier of Love or 21, and seemed to be the sort of recording I needed to listen to to hear the improvements wrought by the 820S.

Moon by Simaudio 820S

Overall, the improvements the Moon Evolution 820S made in the sound had nothing to do with tonal balance, bass weight, or high-frequency extension -- the sorts of differences typically heard with a change in high-end audio component. Instead, the 820S seemed to lower the noise floor of the component(s) it was connected to, resulting in better re-creations of soundstages, more precise images on those stages, and a more complete unveiling of pretty much every musical nuance, such as air around instruments and voices.

Conclusion and considerations

While the differences that Simaudio’s Moon Evolution 820S power supply made to the sounds of the Moon Evolution 650D and 740P were subtle, that’s not to speak poorly of it; instead, it speaks highly of those components’ own internal power supplies. In fact, if powering them with the 820S had transformed their sounds, I would have been suspicious of Simaudio’s engineers’ designs of them in the first place, particularly as the 650D and 740P had been on the market for a few years before the 820S was born. In my opinion, their power supplies are already very good; the 820S is just a little bit better.

But is the Moon Evolution 820S worth $8000? The answer will depend on a few things. If you don’t like the sound of an 820S-compatible Evolution-series component in the first place, then the likely answer is no -- the 820S won’t bring about the sort of wholesale change that might alter that impression. However, if you’re really enthralled by the sound of a compatible Evolution component and have no plans to replace it, then I could see adding an 820S, even if it means moving the needle of sonic performance only a little bit. After all, when you get to the highest levels of performance, even small improvements are hard to come by, which is why they so often cost so much -- it takes so much more effort to realize these gains. For instance, as surprising as this may sound, I could see upgrading the 740P preamplifier with the 820S; the 740P is already a high performer, and it was exciting to hear it sound just a smidge better. Furthermore, the next step up in the Evolution series is the 850P, whose whopping price of $30,000 puts it way out of my and most others’ reach.

Moon by Simaudio 820S

For the 650D alone, the answer is not so clear, though it seemed to benefit more from the 820S than did the 740P. The reason? Simaudio recently released the Moon Evolution 780D streaming DAC ($15,000), which includes their latest technologies but has no CD transport. I’d check it out before I upgraded the 650D with the 820S. (I have no experience with the 780D, so I can’t tell you how its sound compares with that of the 650D plus 820S.) Finally, if you have more than one compatible Evolution component, then the 820S becomes even easier to justify, because the cost of improving the power supply and sound of each component is halved.

You’d think that with such a specialized, limited product, with so few connectors and controls, there would be fewer things to consider. Not so. Simaudio’s Moon Evolution 820S power supply works as well as I expected it to; however, it’s the Evolution-series owner who ultimately must decide if the improvements are worth $8000.

. . . Doug Schneider

Associated Equipment

  • Loudspeakers -- KEF Blade Two and Reference 3, PSB Imagine T3, Vivid Audio Oval B1 Decade
  • Amplifiers -- Audio Research GS150, Blue Circle Audio BC204, JE Audio VM60 monoblocks, Simaudio Moon Evolution 870A
  • Preamplifier -- Simaudio Moon Evolution 740P
  • Digital-to-analog converters -- EMM Labs DAC2X and DA2, Hegel Music Systems HD30, Simaudio Moon Evolution 650D transport-DAC
  • Computer -- Samsung laptop running Windows 10 and JRiver Media Center 20
  • Digital interconnect -- AudioQuest Carbon
  • Analog interconnects -- Crystal Cable CrystalConnect Standard Diamond
  • Speaker cables -- Siltech Classic Anniversary 330L
  • Power cords -- Shunyata Research Venom HC
  • Power distributors/conditioners -- Shunyata Research Venom PS8 and Defender noise reducers/EMI suppressors (2)

Moon by Simaudio Evolution 820S Power Supply
Price: $8000 USD.
Warranty: Ten years parts and labor (with registration).

Simaudio Ltd.
1345 Newton Road
Boucherville, Quebec J4B 5H2
Phone: (450) 449-2212