Sim Audio Moon Series P-5 and W-5

     Sim Audio deserves recognition as a solid state brand of the first rank, alongside well known luminaries such as Jeff Rowland, Krell, and Levinson. And Sim's flagship products, the Moon Series P-5 line section preamp and W-5 power amp, perform on a par with the flagship offerings of these other premium brands, actually surpassing them in some sonic aspects.
     But there is a major difference. Price. The flagship power amps from the big three luxury brands each cost well over $30,000. The Sim Audio flagship W-5 power amp costs just $4795 (and the P-5 flagship preamp, on two chassis, is $3995).
     Like the luxury brand electronics from the big three, the Sim Moon Series play music with a sense of relaxed ease, sophistication, and effortless authority. There is no hint of typical solid state sound, and very little evidence of any kind of electronics intervening between you and your music.
     The P-5 and W-5 actually surpass the sonics of the flagship Levinson and Krell electronics in the difficult upper frequencies, especially in all three treble ranges. The Sim Audio treble ranges are at once stunningly beautiful and richly informative, a very rare achievement, especially for solid state circuitry. The finest treble nuances are exquisitely delineated with excellent speed, extension, and clean purity. Yet there is not the slightest hint of clinical sterility or artificial hardness in the Sim's revelation of musical detail. Indeed, if the program material sounds liquid, the Sim reveals this liquidity with a natural musical beauty that will have you swearing you're listening to top class tube electronics.
     The Levinson and Krell electronics don't do as well as the Sim in handling music's trebles. Their trebles generally sound somewhat smoothed down, even rounded or rolled off sometimes -- not as fast, extended, and detailed as the Sim's trebles. Their trebles are somewhat smudged, fuzzy, defocussed -- not as individuated and focussed as the Sim's. Their trebles are somewhat dirty, sometimes sounding sandy or grundgy -- not as clean and pure as the Sim's.
     Yet, with all its excellent detail, focus, and clean purity in handling music's trebles, the Sim never sounds analytical, sharp, or sterile, as some other solid state electronics can and do. Instead, music's trebles emerge from the Sim with exquisite finesse, a sense of relaxed ease, and a delicate sweetness (which is not overly syrupy as in some tube amps).
     In a word, the Sim is musically natural. It is richly informative of musical detail (more so than the Levinson and Krell), and simultaneously very easy to enjoy listening to. What is responsible for this rare combination that makes up the Sim sound? Sim's technical descriptions report that their circuitry is designed for maximum speed and detail, but then employs no loop feedback, which might tend to harden sound. This gives them the sweet delicacy, the musical naturalness we hear. Furthermore, the solid state devices are FETs and MOSFETs, which tend to sound sweeter than bipolar transistors.
     The closest sonic cousin to the Sim sound is the sound of the Jeff Rowland flagship electronics, such as the $32,000 Model 9 power amp and the $14,500 Coherence II preamp. These flagship Rowlands also feature trebles that are detailed yet sweetly delicate. But there's a big difference in price.
     The Sim sound is also similar to the Jeff Rowland sound in the midranges, which have a polite, even reticent personality. This midrange politeness makes for relaxed easy listening, and is excellent at portraying a stage full of musicians at a distance. But it is not so effective at bringing the musicians into your listening room, with up front immediacy and presence, on those recordings that were miked this way.
     This midrange politeness might be traceable to the Sim's use of FETs and MOSFETs, which sometimes tend to have a polite, warm, dark, or recessed sonic personality (as opposed to bipolar transistors, which often tend to sound lean, thin, hard, and cold).
     If you want the exciting midrange slam that some recordings deliver by putting the musicians up front, right in your listening room, indeed almost in your lap, then you would be better served by electronics with more midrange presence. The Sim electronics, like the Jeff Rowlands, put the musicians at a slightly greater distance, and refuse to dump the musicians in your lap even when the recording was made that way. Their midrange politeness also implies slightly less midrange bite and dynamics.
     There's room for both kinds of amplifier sound in this audio world, to match up with various listener preferences. Listeners preferring the relaxed, musically natural qualities of the more polite midrange might well find the up front amps too aggressive, and they'll find the natural musicality of the Sim sound very enjoyable and richly rewarding. On the other hand, those listeners preferring the exciting immediacy and dynamics of music through the up front amps might well find the polite amps to be too indirect, wimpy, or uninvolving. Our job is to tell you all aspects of a product's sonic personality, your job is to pick the personality that suits you best.
     The overall tonal balance of the Sim electronics is musically consistent, and fits in well with the sense of relaxed ease that the Sim electronics evince, which makes music listening so enjoyable. The sweet and delicate trebles fit in well with the polite, unaggressive midranges. Then a rich warmth region assures that these Sim solid state electronics don't sound at all lean, cold, or thin (as many other solid state electronics do, especially those in Sim's moderate price bracket). This rich warmth brings out the body of instruments and vocalists. For example, on massed strings you can hear the wood of the bodies, and then the delicate sounds of the gut strings, better than from other solid state amps, since there is less midrange glare blocking or competing with this musical information. Indeed, the Sim sonic motto could well be 'less glare, more music'.
     The Sims' sonic personality traits, as described above, seem similar in both the P-5 preamp and the W-5 power amp, and pretty equally divided between them, each contributing about half to the sonic personality of the pair taken together. Thus, if you happen to find that this pair is too polite in the midranges for your taste, you might consider using just one of them, and pairing this one with another brand of product. For example, we think that the P-5 would make an ideal line section for feeding the McCormack DNA-2LAE, since the slight polite liquidity of the former would ideally balance the slight electric aggressiveness of the latter.
     Moving on down to the Sim's bass region, we find it to be excellent in quantity (not too lean, not too bloated) -- but only pretty good in quality. Bass transients seem to have a rounded, poofy attack rather than really sharp impact or solid slam. To its credit, the Sim is not boomy, muddy, or overly heavy in bass quality (as are most tube amps, and some solid state electronics with poorly staggered bass poles).
     These Sim electronics are spec'd as being DC coupled, so their small signal frequency response is by definition perfect for the low bass region. What then might cause the poofy bass quality? We suspect that the W-5's lack of feedback might be impeding its ability to control the woofer as well as some other amps can (like the McCormack DNA-2LAE). Ironically, this lack of feedback is probably the chief technical factor responsible for the W-5's ravishing trebles being so sweet yet detailed. Which might prove again the old saw in the engineering world that you can't have your cake and eat it too. If we had to pick a weak area in the Sim, it would be this bass quality. Of course, if you are fanatic about bass quality, you probably have a subwoofer with its own dedicated amplifier, so the Sim W-5 could serve ideally as your main amp for the rest of the spectrum.
     The Sim's stereo imaging is excellent, with superb stage width and depth. The Sim's tonal balance naturally affects one aspect of imaging, the apparent distance of the performers. If the recording is a close miked up front recording, some other amps can place the musicians even forward of the speaker line (closer to you than the speakers), but the polite midrange tonal balance of the Sim puts these same musicians slightly farther than the speaker line (which is fine if you prefer musicians to be at this more comfortable distance rather than screaming in your lap).
     These Sim Moon electronics sound very clean and pure (distortion free), in spite of the fact that they use no feedback to lower distortion. In fact, they sound even cleaner in the trebles than most other amps, even though most of those other amps do employ feedback to lower measured distortion. As noted, these Sim electronics sound cleaner than luxury megabuck electronics from luminaries like Levinson and Krell (especially in the difficult trebles, where distortion usually rises in amplifiers). And, as discussed above, in spite of being so clean, these Sim electronics sound delicate, sweet, musically natural, and relaxed, never sterile or clinical.
     Since there is no loop feedback to lower distortion, how does these Sim products manage to sound so clean and pure? The Sim circuitry is fully balanced differential, which cancels out even order distortions. As to odd order distortion, loop feedback actually raises higher odd order distortions (which tend to sound ugly and artificial), so the absence of loop feedback in the Sim might actually work to minimize these ugly and artificial sounding higher odd order distortions, thereby keeping the Sim sounding sweet and musically natural. That would leave only one significant kind of distortion unaddressed, namely third order distortion, which is a low order (not high order) odd harmonic distortion. However, compressive third order distortion is the predominant distortion in an analog master tape, and we know that it sounds relatively benign and musically consistent.
     The Sim P-5 and W-5 are also exceptionally quiet, both electronically and mechanically. You just can't tell whether they're on or not, except by looking at the lights. There's nary a whisper of noise or hiss from the speakers. One key factor here is the P-5's use of a totally separate shielded chassis for its power supply. It's very unusual for a line section to have a complete power supply on a separate outboard chassis, since the signal levels are much higher than in a phono front end, and therefore are less vulnerable to noise pickup from nearby power supplies sharing the same enclosure space. But Sim evidently felt that the benefits in lower noise would be worth the extra expense of building a separate full size chassis enclosure, and the proof is in the pudding, as we hear (or rather can't hear) in the final product.
     This black background of silence also doubtless further helps the Sim to render the most subtle treble nuances so delicately and individually, since there is no noise to compete with and confuse this subtle musical information. Recall from earlier IAR measurements that treble details actually take the form of little squiggles riding on the larger waveform of bass and midrange information, and these little squiggles can easily get swamped by competing noise.
     The W-5 and P-5 come equipped with built in machined metal feet, and optional screw in spikes. These can be used to mechanically ground or couple these units to the platform or suspension of your choice. These metal feet can also be used to effectively couple to rubber isolating feet, providing a well defined path of mechanical integrity for isolating the chassis. We far prefer having these solid metal feet as defined coupling points, as opposed to the typical electronics product that gives you nothing but an expanse of flimsy bottom plate with which to couple to the chassis. It's worth noting that the Sim's machined metal feet alone would cost you a couple of hundred dollars on the market. By coupling to these metal feet in a variety of ways, you can optimize the setup of these Sim electronics to best match your mounting environment, and of course each different type of setup will affect the sound slightly.
     Construction quality is excellent, especially at the price point of these products. Noteworthy features include a very short signal path length in the preamp, achieved in part by relays to switch all functions (including volume and balance). The relay based preamp also allows full remote control of all operations, via the included remote. The volume and balance controls are actually switched attenuators, using discrete resistors, so there are no wipers or nonlinear contact resistances in the signal path. Furthermore, the attenuator employs only two resistors per volume control setting, so the signal does not go through cascades of multiple resistors as in some other switched attenuator configurations. Also, the switched resistor arm is the arm to ground, not the arm in series with the signal (a topology first seen from Paul McGowan of PS Audio fame), so that the switch contact (in this case a relay) is not in series with the signal (though it still does affect the signal, since it is in the path of the voltage dividing action). An AC3 input on the P-5 preamp operates always at full volume level, so that all volume level control is handled by your home theater processor for this input.
     The fully balanced circuitry can accept both balanced and unbalanced inputs, both at the preamp and at the power amp. The W-5 power amp even has RCA inputs for a balanced signal, as well as the usual XLR (which also allows you to invert the phase polarity of either a balanced or unbalanced incoming signal). The W-5 can also be strapped for bridged mono operation.
     The W-5 is rated at 175 watts per channel in stereo mode. This gives it enough headroom to maintain the Sim trademark sound of relaxed ease, even at fairly high levels. On the other hand, the W-5 doesn't sound that loud when playing loudly, since the tonal balance has a polite midrange and since the low bass has a poofy attack quality.
     Package design is worthy of a luxury marque selling for far more money. The chassis are massive (the P-5 line section weighs an astonishing 35 pounds), with thick front plates having a sophisticated satin finish, and discreet blue lights to indicate power on. The red LED display, showing function and volume level, can be shut off (for better sound and less visual distraction). The chassis aesthetics feature an interesting counterpoint of shapes: rectangle (the front plate) vs. cylindrical (the heat sinks), and this aesthetic is even repeated in the remote control. The two chassis of the P-5 line section can be easily positioned side by side or vertically stacked.
     There are some nits to pick regarding minor points of ergonomics. The remote has faux heat sinks to echo the aesthetics of the main chassis, but this makes it needlessly heavy, and it becomes fatiguing to handle. The included CD player remote buttons are at the very bottom of the remote, where they are impossible to manipulate while holding the heavy remote. There's no clue as to which end of the remote to open to install the batteries, the screws were jammed on so tight that the included allen wrench stripped, and the screw threads stripped the receiving threads on the faux heat sinks.
     The instruction manual correctly advises you to plug the power amp directly into the wall for best sound, yet there is no power switch on the front panel of the power amp, and (as everyone knows) you should turn off a power amp when making any system changes or when leaving the system unattended (since power interruptions can cause speaker blowing system burps when power is restored). Indeed, the Sim instruction manual doesn't even mention that the power amp even has a power switch at all, and you must be clever enough to discover the tiny unlabelled pushbutton on the rear panel for yourself.
     The instruction manual speaks of a tape monitor loop, and the preamp has a tape monitor switch, but in truth there is no tape input to monitor and no loop function at all. The P-5 does have a tape output (but not any tape input), and the so-called tape monitor switch merely switches the tape output jack on or off. The instructions fail to guide you as to what use this switch might have, but there is a potential advantage to turning it off when not making a tape recording, since the nonlinear input loading of the tape recorder (or CD recorder) circuitry might adversely affect the sound coming out of the main preamp outputs. The instruction manual contains other gaffs, such as boasting that there are no capacitors in the signal path to degrade sound, when in fact there are many capacitors in that part of the signal path called the power supply.
     Fortunately, none of these minor nits affect the sound, which is what really counts. How do the Sim electronics fare against similarly priced competition? Most of the similarly priced competition sounds much cruder, more artificial, more strained. It simply can't play music with the relaxed ease and delicate naturalness that flows so effortlessly from the Sim electronics. We see only a couple of other units out there that are any real competition for the flagship Sims, anywhere near their price.
     If Sim's flagship P-5 and W-5 are too rich for your budget, there's a full line of Sim Audio electronics at less expensive price points, which share the same design philosophy and thus presumably at least some of the same sonic virtues. Sim's premium Moon series has other preamp and power amp models less expensive than the flagship P-5 and W-5. Then there's a whole separate series from Sim called Celeste. And finally, Sim is now also introducing a new integrated amp (which may be the first integrated amp to give serious competition to the very musical Audio Refinement Complete).
      The bottom line sonically is that the Sim flagship electronics can hold their own against competing flagship electronics costing 6 times more, even surpassing these competing units in some sonic aspects. The Sim sound matches the luxury electronics in playing music with a sense of relaxed ease, sophistication, and effortless authority -- while surpassing them in many aspects, especially in the difficult trebles, where it is at once more informative and also more musically enjoyable. It's a real tribute to Sim that we found ourselves comparing the sound of their moderately priced units to the luxury luminaries costing 6 times more, and often discovering that the Sim is superior. That is a remarkable achievement, and makes the W-5 and P-5 a real bargain for those of you seeking high end solid state.

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