Simaudio Moon P-5 preamplifier & W-5 power amplifier Follow-up from May, 2001

A Follow-up review by Kalman Rubinson appeared in May 2001 (Vol.24 No.5):

Like everyone else, I go to the January CES to see and hear what's new. I was greatly interested in Simaudio's new multichannel amplifier and their new analog FM tuner, but Lionel Goodfield, their director of media relations and marketing, cornered me: he wanted me to do a Follow-Up report on the $4795 Moon W-5 amp, which I'd reviewed in the March 1999 Stereophile. After all, he said, the many changes and improvements that have been made to the amp over the years justify such a re-examination.

I could see through that. The W-5 was placed in Class A of Stereophile's "Recommended Components" in 1999 and will therefore soon be in imminent danger of being removed from the list, per the magazine's policy, for lack of recent re-audition by a Stereophile reviewer.

I let Goodfield twist my arm for three reasons. First, I did love the sound of the W-5. Second, the W-5 I reviewed was an early production sample, and any significant improvements might affect the amp's sound; if so, they should be reported. Third and most important, my ears and system have evolved greatly since: This could be an opportunity to reevaluate my own comments and reactions. Besides, I was already in the throes of a marathon power-amp review roundup. So what's another amp around the house?

Externally, this latest W-5 is identical to the original. I refer you to my original March 1999 review for a full description of this beautiful and well-executed design in its gracefully elliptical chassis. In fact, if Simaudio and/or this report didn't detail what's new, one would have no inkling of any functional changes. The manual, however, is greatly improved; it's more readable, and the connection instructions are now unambiguous.

The internal changes are straightforward: Filter capacitance in the power supply has been increased by 40,000µF. (Each of the eight caps was increased by 5000µF, for a total of 216,000µF vs the previous 176,000µF.) Along with some redesign of the proprietary toroidal transformers used in the power supply, this should result in better reproduction of deep bass, something the W-5 was already very good at.

The passive filter circuitry used in the input stage (which limits bandwidth) was modified to increase upper-frequency extension from 80kHz to 270kHz. This will have no effect on perceived high-frequency extension, but it does move any phase shift due to the filter further from the audible range, in much the same way as oversampling does in DAC design.

Finally, the output stage now uses 10 (vs 8) Motorola bipolar output transistors per channel. This could result in an increase in available output current—although, again, the original W-5 was itself a formidable powerhouse, "almost doubling its power delivery each time the load impedance was halved...and [delivering] a staggering 1480W into 1 ohm," as John Atkinson wrote in the "Measurements" section of my 1999 review.

For this Follow-Up, I fed the W-5's XLR balanced inputs from the Sonic Frontiers Line-3 preamplifier via JPS Labs Superconductor2 interconnect, and the Revel Ultima Studios from the W-5's very substantial multiway terminals via short lengths of AudioQuest Gibraltar double biwire speaker cables.

Like the original version, the new W-5 proved to be a marvelous amplifier. Auditioned exclusively with the Revel Studios, the W-5 was impressive: there was no shortage of power and control, large dynamic shifts were handled with aplomb, and microdynamic shadings—so important to the subtle communicative powers of great vocalists—were true. The W-5 was smooth across the audible range, and not at all embarrassed by the Revel Studio's revealingly transparent midrange and pure, grain-free treble.

I found the W-5 stalwart in the lower bass (below 200Hz), and just a bit more imposing than expected. Cold from the box, the sound was rather too mellow, with noticeable opacity in the bass—but that problem was cured by a few days of continuous operation. From then on, the bass was excellent—tight, defined, extended, and powerful—but there was a little more of it than seemed right in my system.

I've experienced this phenomenon before: otherwise excellent performance with a bit of bass prominence in exactly the range most influenced by speaker placement and room acoustics. I've taken great pains to situate the Revels so that the bass is as smooth and clean as possible with my reference McCormack DNA-1 Rev.A and Sonic Frontiers Power-3 amplifiers. In fact, at the end of the audition, we had new acoustic drapes installed on the windows behind the speakers. With the drapes closed but no other changes made to the room, the Moon W-5 sounded just right in the bass, the other amps just a bit thin. So set aside the bass issue as system-specific and relative, not an inherent fault of the W-5. If you think your system could use a tiny touch of oomph at the bottom, the W-5 may be the perfect amp. After all, one pays absolutely no price for the solidity and slam; its performance was otherwise beyond reproach, in the bass or anywhere else.

I easily preferred the Simaudio Moon W-5 to the Bel Canto EVo 200.2 that I reviewed in March for its evenness of response and great dynamics. Against the DNA-1 Rev.A the W-5 sounded less etched but no less detailed in the midrange and high frequencies. It was also more transparent and just a bit less forward than the McCormack. Comparing the W-5 to the SF Power-3 monoblocks was like comparing equally fine silk velvet and silk damask: personal preference and suitability to the situation distinguished them much more than issues of ultimate quality. Given my system's current arrangement, the Power-3s seem to impose no character at all on the sound, while the W-5 added a little richness by way of bass warmth. If I moved the Revels farther out into the room or just closed the drapes, my preferences wavered.

The new W-5 sounded very much as the original did, as described in my March '99 review: powerfully extended, well-controlled low frequencies, transparency, delicacy, and prodigious dynamic power. Audio memory is evanescent, however; I wouldn't like to say if the current W-5 is significantly better than the original. But if you buy a new W-5 in this millennium, you'll get an amp that excels by today's standards. It's capable of driving anything with power and panache, and of satisfying the most particular listeners. I greatly enjoyed using the W-5 in late 1998, and enjoyed it just as much in early 2001. Simaudio really didn't need to twist my arm.—Kalman Rubinson

Manufacturer's Comment
Editor: Simaudio Ltd. would like to thank Kalman Rubinson and Stereophile for "answering the call" to do a Follow-Up editorial on the Moon W-5 power amplifier, and we greatly appreciate the quick turnaround. We felt that the upgrade made to this component since the original review in March 1999 merited a listening. Besides, as KR stated, the W-5 will "soon be in imminent danger of being removed from the 'Recommended Components' list," and our intention is to continue producing this amplifier well into the foreseeable future.

Essentially, the changes that have been made in the Moon W-5 don't alter its sonic signature; they simply allow it to "push the sonic envelope" a little further than before. The most noticeable result in this case is that its output has been increased by a factor of roughly 15%. In listening tests done at our factory with a variety of in-house loudspeakers, we consistently noticed sonic improvements deemed relevant enough to justify implementing these changes. For W-5 owners wondering when this happened, units manufactured from August 1999 on are considered "current production."

The only explanations I can derive from KR's statement concerning significant differences between the original and current W-5s are: 1) as he stated, "Audio memory is evanescent," especially when you review many high-performance audio components and experience a gap of more than two years between listenings to a particular one; and 2) the Revel Studio loudspeakers were used exclusively here—last time around, this was not part of KR's reference system. In any event, KR clearly hears exactly what the W-5 is capable of, and for this we are very grateful.

Thanks, Kal, for once again recognizing all of the many strengths of the Moon W-5 power amplifier.—Lionel Goodfield, VP Marketing & Media Relations, Simaudio