Aesthetics / specs / setup:

The ‘Sims’ as they shall be referred to during the remainder of this review, are a fully balanced differential mono-block amplifier capable of producing 750 watts into 8 ohms and 1400 watts into 4 ohms.
According to the SimAudio website ( the amp uses “technology featuring a no overall feedback circuit and bipolar output devices”.

Aesthetically the Sims are very handsome and quite minimalist in appearance. They adopt an integral framework, which provides both lifting handles and spiked feet, allowing for easy handling and lifting from the top of the amplifier and at the same time negates the need for a spiked amp stand.

The amps run cool and do not therefore require hefty heatsinks as found on Krell amps, for example. The result being a relatively light and compact amp at a mere 71 LBS each.

The amps have both balanced and single ended inputs, use a small nipple switch for on/off operation, and disappointingly lack a second set of speaker binding posts. Other than that there isn’t much else to remark on as far as aesthetics and connectivity are concerned.
Initially I used the amps with their integral brass spikes into the carpet. This arrangement doesn’t provide much clearance on the underside of the amp and I was a little concerned about ventilation. Coming from the Krell MD300, I was half expecting a black scorch mark on the carpet, but after an hour or so of operation it was evident that these amps run exceptionally cool. The main reason for their relative efficiency is that the design runs class A for the first 10 watts only, thereafter switching to AB.

Having recently moved my system into another part of the room, I no longer have a dedicated amp circuit, so I have a less than optimal arrangement with both amps pulling juice from the same wall outlet. Pulling juice is probably not an appropriate term for these puppies, with a peak current rating of 85 amps each, or 35 amps continuous, it’s more a case of draining than pulling.

The Sound:

First let me give a little background on the decision to buy SimAudio Moon W10 Monoblocks. I’m using Magnepan 3.6R speakers in quite a large room. I’ve learned the hard way through extensive trial and error that these speakers need gobs of power to come alive. I wont list all of the amps that I’ve tried, but 200w/channel Cary V12 Monoblocks, Krell FPB200 and most recently Krell’s MD300 monoblocks, have all been through my system. Non of these so-called ‘muscle’ amps ever really got to grips with the Magnepans in a way that could be described as ‘authoritative’. Of course the Krell MD300’s came closest, with their 650 watts into the Maggie’s 4 ohms, but they always sounded muddy through the midrange, and a little lacking in extension. So the Sim’s on paper at least, seemed to remove any lingering doubts of having sufficient power on hand.

I had company on the day these amps arrived, so I courteously offered Steve the sweet spot for the first few tracks. The amps were stone SimAudio Moon W10 Monoblockscold, having been sitting in the back of a UPS van on a 20 degree day.

They clearly needed some gentle coaxing to get them up to room temperature. However, with the amps cold, and me sitting some 4 or 5 feet away from the sweet spot, I could tell within the first few notes that there was something special at work. I could hear a warmth and depth to the sound that no other amp has produced in my system to date.

After 30 minutes or so of warm up, I assumed position in the sweet spot, anxious to see if my off-axis initial impressions were supported from the critical listening spot. They were, but with a small reservation or two. There was tremendous depth and sweetness to the sound, but with a slight smearing in the midrange, and slight lack of clarity. This gave instruments a slightly more homogenized sound without a clearly delineated soundstage.

Listening to the instrumental track 3 on the Ani De Franco’s Reckless CD, there wasn’t the same attack, bloom and decay to the acoustic guitar notes. It didn’t have the impact that was evident with the Krell amps that had just been replaced.

It was a little irritating to have this apparent deficiency, but I tried to focus more on the strengths that these amps clearly have over the Krells.
I’ve never heard amps fill up the soundstage like these do. A few days before they arrived, I’d been experimenting with speaker position, and moved them apart by almost 18 inches, to approximately 8’ between inner edges. This seemed too much, and though there was a nice sense of scale and stage width, the leanness that the Krells had exhibited in my system seemed to be exaggerated. With the Sim’s in place, the soundstage became completely populated without any apparent leanness and with good center fill energy.

Bass was deep and tight. There’s a sense of weight and authority that I thought was probably max’d out when I added the Krells, but the Sim’s provide more, and in spades. There is also naturalness to the bass that I haven’t heard before. Playing tracks from the ‘Steve Green Trio’ CD, which is my reference for the reproduction of acoustic bass, the instrument sounded so tight and defined, yet notes had all the bloom and reverberation that you would expect to hear from a ‘real’ and ‘live’ instrument.

I enjoyed this ‘new’ presentation for a few hours then set about trying to correct some of the weaknesses. I moved the amps off the carpet and sat them on marble slabs, still using the integral spiked feet. This seemed to pull a little fullness and bloom out of the midrange and tightened focus a little. Later, I added large brass cones under the chassis of each amp, effectively making the integral feet redundant. This further increased focus and added back the dynamic ‘snap’ and impact, acoustic guitar strings now had that sense of attack, bloom and decay that I’d missed with the amps spiked into the carpet.

A week later, I removed the marble slabs and used the large brass cones under the amp chassis and into the carpet. The change was subtle yet apparent and this arrangement so far has brought the best results.

The top end of the SimAudio Moon W10 is also excellent. There is great extension and clarity, yet with a sweetness to the sound that is generally found in only the best solid state amps. I have some room acoustic problems that need to be resolved resulting in a slight glare at the higher frequencies and a little ringing through the midrange. But I have a sufficient handle on those problems to know when it’s the room and not the equipment. I don’t detect anything in these amps that is anything less than first class reproduction of sound, across the frequency spectrum. The Krells presented a tad more depth to the soundstage, but this may have been a product of the leaner midrange, when all said and done.
The Krells presented the stage level with the front of the speaker and pushed it backwards. The Sim’s present the sound slightly forward from the front of the speaker and stretches back almost as far as the Krell, so overall, there is a greater sense of depth and 3 dimensionality with the Sim’s.
Bass performance was very good with the Krell, but better with the Sim’s, the sense of weight and authority is first rate.
The midrange is where the Sim’s really excel. They provide a full, liquid and coherent soundstage that fills up the space between speakers providing a seamless whole.
The highs are clear and precise without drawing unwanted attention in a way that can quickly become fatiguing. There is an excellent retrieval of detail, the subtle information around the pluck of a double bass string for example, is retrieved in a way that I haven’t heard before.

One small discovery that has taken a couple of weeks to appear, and has resulted in a very pleasant surprise: the amps need to be powered up continuously for much longer than I’ve ever heard from another piece of equipment, before they sound their best. I’m not talking about hours, rather days.

I’ve had a few comments from other Sim users on Audiogon that have concurred with this. The sound of these amps really starts to bloom after 3 or more days of continuous AC. The soundstage takes on more depth and detail retrieval is improved quite noticeably. The downside comes when experimenting with different power cords or moving things around. You definitely loose a whole degree of performance even with a 5 minute power-down, and it takes days for it to reappear.

These are by far the best amps I’ve heard in my system. I can’t get enough music right now, which tells me one important thing, these are very musically engaging amps!
However, I believe that the full potential of the Sim’s is not being realized presently, due to my poor AC installation. That will be rectified in the next week or so and I’m hopeful for another step forward in performance.
I would heartily recommend these amps to anyone requiring extra weight and authority in their system without losing any sense of realism or finesse.