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Equipment Review
May 2004

Audio Electronic Supply SixPac Mono Amplifiers

by Andrew Chasin



"A breakthrough in terms of tube-amplifier price and performance."

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Review Summary
Sound "These amplifiers exhibited all of the traits for which tube amplifiers are revered -- warmth, body, palpability -- without sounding mushy, bloated, or soft." "When the amps were configured for 4-ohm operation, their bass was surprisingly deep and taut with excellent pitch definition…." Their "luxuriously silky midrange…did justice to vocalists"; "high frequencies were…beautifully served."
Features "Dennis Had-designed, all-tube, point-to-point-wired monoblocks" that are "a class A/AB push-pull design based on the venerable EL34 output tube -- six per channel for a total of 50 watts per chassis."
Use Andrew "left the negative feedback switch in its 0dB position for all of [his] auditioning" and preferred the amps' 4-ohm outputs with his 8-ohm ProAc speakers; "tube rollers will be happy to hear that the SixPacs will accept a wide variety of output tubes, including the 6550C, 6L6, KT88, and KT90."
Value "Benchmark products at their price point."

I committed the ultimate audio sin: I bought a pair of Audio Electronic Supply SixPac mono power amplifiers sight unseen and sound unheard. I’m not sure what possessed me to do such a thing. Perhaps I was longing for a touch of the Cary CAD-805 magic that casts its spell on me each time I am fortunate enough to hear a pair of these amps at a show or a high-end dealer. Perhaps I felt that, with a move to a smaller listening room and to a smaller pair of speakers, the 175Wpc Simaudio Moon W-5 I’d been using for years was overkill. Or perhaps I was simply looking for a relatively cheap way to reinvigorate my interest in things audio and, with any luck, improve the sound of my system in the process.

Whatever the reason, I found myself calling Dennis Had, the Big Kahuna at Audio Electronic Supply and its sister company Cary Audio, and placing an order for a pair of SixPacs. A week later, the amps were in my system. Six months later, they’re still there.

Description

Although there are a couple of dealers that have SixPacs to demo, unless you’re in New Jersey or Uplands California, you’re going to have to do what I did and order the amps directly from Audio Electronic Supply sans audition. The lack of a dealer network (and the commensurate dealer markup) is what allows AES to sell these Dennis Had-designed, all-tube, point-to-point-wired monoblocks for a paltry $2400 USD per pair. I’d guess that a pair of SixPacs would go for something like $5000 if they were sold at your favorite audio salon.

Unlike Dennis Had’s esteemed single-ended CAD-805 and CAD-300SE power amplifiers, the AES SixPacs are a class-A/AB push-pull design based on the venerable EL34 output tube -- six per channel for a total of 50 watts per chassis at .55% THD. Aside from the six output tubes, each channel incorporates a duet of input tubes: a 12BZ7 for input gain and phase inversion (the more common 6922 was the original choice, but, according to Had, "The sonic merits [of the 12BZ7] were not subtle") and an EL84 as a current source for the 12BZ7. Tube rollers will be happy to hear that the SixPacs will accept a wide variety of output tubes, including the 6550C, 6L6, KT88, and KT90.

The relatively small SixPacs (8"H x 8"W x 12 1/2"D) each weigh in at a chunky 33 pounds. This weight is primarily attributable to the amplifier’s hefty transformers, which occupy a good portion of the chassis real estate.

The tasteful-yet-Spartan front panel of each amplifier contains two toggle switches surrounding a red LED. The left switch toggles the amplifier’s power on/off and the right switch enables/disables 10dB of negative feedback. The red LED is illuminated when the amplifier is powered on. According to Had, enabling the 10dB of negative feedback results in better bass control, but poorer soundstaging. Because the SixPac’s bass control seemed more than adequate and I typically prefer zero-feedback designs, I left the negative feedback switch in its 0dB position for all of my auditioning.

Around back, loudspeaker and line-level hookup to each monoblock is accommodated via a single pair of five-way binding posts and a gold-plated RCA jack respectively. An IEC receptacle enables power-cord twiddling, and a slow-blow fuse is included for protection. An impedance switch is also provided to configure the output for either 4- or 8-ohm operation.

A rear-mounted bias pot (one per channel) used in conjunction with a user-supplied multimeter makes biasing the SixPac’s output tubes a snap. Bias measurements can be taken by connecting the multimeter to an output jack on the rear panel of each monoblock using a cable supplied with the amplifiers. My only gripe with this procedure is that the bias pot is far too sensitive -- barely touching the control causes the bias setting to change dramatically, making it difficult to zero in on the correct setting.

While the SixPacs aren’t likely to win any industrial-design awards, they are attractive in an understated way, with a chassis that’s neatly finished in basic black textured steel and garnished with a simple black anodized-aluminum faceplate with gold silk-screening.

Review system

My review system has been fairly stable for some time, and includes a VPI Aries turntable (with Mk.V platter and bearing)/VPI SDS motor controller/Graham 2.0 tonearm/Transfiguration Spirit phono cartridge analog rig feeding a Hovland HP-100 preamplifier with MC phono stage. Until the SixPacs arrived, amplification was courtesy of a Simaudio Moon W-5 solid-state amplifier. Loudspeakers were ProAc Response One SCs. Cables were primarily Harmonic Technology Pro-Silway Mk.III interconnects, Pro-9 Plus loudspeaker cables and Pro AC-11 power cords. Phono cable was the wonderful Hovland Music Groove 2. I also logged some quality time with the terrific Shunyata Research Aries interconnects and Lyra loudspeaker cables. All electronic components were placed on a Finite Elemente Pagode Master Reference rack and plugged into a Richard Gray’s Power Company 400S Mk II power conditioner. The ProAc Response One SCs were placed on sand-filled Target R4 stands.

The SixPacs were allowed to break in for approximately 50 hours before they were carefully re-biased and ready for some serious listening.

Listening

From the first moment I listened intently to the SixPacs, I knew I was in for a treat. These amplifiers exhibited all of the traits for which tube amplifiers are revered -- warmth, body, palpability -- without sounding mushy, bloated, or soft. When the amps were configured for 4-ohm operation, their bass was surprisingly deep and taut with excellent pitch definition -- on par with some of the better solid-state amplifiers I’ve heard. The 8-ohm mode delivered an even greater sense of bass heft, but I preferred the coherence and overall musicality of the 4-ohm mode, even though the ProAc Response One SC loudspeakers I used present a nominal 8-ohm load.

I recently happened upon a vinyl import of Steely Dan’s Everything Must Go [Reprise 9362-48435-1]. This is a truly great-sounding pop record -- right up there sonically (and musically) with Gaucho and Aja. (Everything Must Go is the first album I downloaded from Apple’s iTunes music store, although I’ve yet to bring myself to connect my iPod to my audio system to compare the AAC-encoded and vinyl versions.) I was stunned by the weight and impact of this LP when heard via the little SixPacs. Bass drum in particular had the kind of solidity and punch that I normally attribute to much larger and considerably more expensive amplifiers. Besides having the requisite low-frequency depth, well-recorded bass guitars, like those heard on "Wait" from Sarah McLachlan’s The Freedom Sessions [Arista/Classic Records RTH-2000], exhibited an organic quality that continually captured my attention. If pressed, I’d have to say that the featherweight, all-tube SixPacs actually bettered the hernia-inducing solid-state Simaudio Moon W-5 in the bass department -- if not on an absolute "oomph" scale then certainly in terms of palpability.

The SixPacs were faithful to their all-tube pedigree, providing a luxuriously silky midrange that did justice to vocalists as diverse as Cassandra Wilson (New Moon Daughter [Blue Note 7243 8 37183 1 3]), Sarah McLachlan (the aforementioned The Freedom Sessions), Ella Fitzgerald (Ella Swings Lightly [Verve MG VS-6019]), and Aimee Mann (Lost in Space [Mobile Fidelity 21797-12781]). Lost in Space has become a particular favorite of mine -- a terrific blend of great music and sound puts this MoFi LP on my short list of candidates for vinyl reissue of the year. Through the SixPacs, Mann’s voice on the sparsely instrumented "This is How it Goes" and "It’s Not" was literally goosebump-inducing. This was a most beautiful and all-too-rare synergy between hardware and software.

High frequencies were also beautifully served by the SixPacs, the amplifiers possessing a level of top-end refinement that belied their budget price. The sound of the ride cymbal, for example, that lives in the left channel on Sarah McLachlan’s "Ice," from The Freedom Sessions, rang truer than I’ve ever heard before. Ditto for other percussive instruments and high strings, which seemed free of any hash or grit that afflicts lesser products. Perhaps it was a particular synergy between the SixPacs and the Response One SCs, but this pairing provided one of the most natural high-frequency presentations I’ve heard in my listening room. This is high praise indeed for two products with decidedly real-world price tags.

Tube amplifiers are not typically known for their superior detail retrieval. If anything, they are often characterized as "soft" and "pleasant" rather than "transparent" and "revealing." But the SixPacs were different. Very quiet for an all-tube product (aside from some slight transformer hum), the SixPacs seemed to unearth detail that I hadn’t been consciously aware of before. Faint background noises, the subtle reverberation of a guitar’s strings, or even more intentional musical sounds buried deep in a complex mix were all more obvious through the SixPacs than other amplifiers I’ve auditioned in recent memory. Oddly, song lyrics also seemed to be more intelligible as well -- I lost count of the number of times I was listening to a familiar record while working and suddenly understood a vocal line that never quite made sense before. I always hesitate to label a component "detailed" as this term has almost become synonymous with "etched" and "hard" in some audiophile circles. In the case of the SixPacs, detail was revealed in a natural, unforced way that urged me to explore the complexities of a musical composition.

Even with their modest power rating, the SixPacs could reach high SPLs without strain with the ProAc One SCs. Even on demanding rock material such as Dire Straits’ Making Movies [Warner Bros. 7599-23480-1] played full-tilt, the little SixPacs remained unperturbed (I wish I could’ve said the same for my wife who was trying to watch TV in the adjoining room). I didn’t have an opportunity to audition the SixPacs in a room as large as my old 400-square-foot listening/living room, but I see no reason why they shouldn’t be capable of filling a sizeable space when coupled with a reasonably sensitive loudspeaker.

Dynamically, the SixPacs were hard to fault, especially at the micro level where subtle volume gradations were handled with aplomb. If I had to level one minor criticism at the SixPacs (hey, nothing’s perfect!) it would have to be in the area of macrodynamics, which sounded ever so slightly blunted on certain material. That said, this was a very minor characteristic and rarely, if ever, diminished my enjoyment of music through these truly wonderful little amplifiers.

Comparisons

On hand for comparison during the review period was a real smorgasbord of power amplifiers ranging from the solid-state Simaudio Moon W-5 ($4995, my long-term reference) and Coda 12.0 ($6550) to the tube/solid-state hybrid Blue Circle BC28 ($3995).

The two powerful solid-state behemoths edged out the diminutive SixPacs in terms of macrodynamics and deep-bass impact. The Blue Circle BC28 won the soundstage-width competition, with a perceived soundstage that extended further beyond the loudspeakers than any of the other amps used for comparison. The BC28 also seemed to produce greater bass depth than the SixPacs (likely owing to its solid-state output stage), although, as mentioned previously, the SixPacs’ bass reproduction was truly impressive for a 50W all-tube design. On the plus side, the SixPacs were more transparent in the upper midrange/lower treble than either the BC28 or the two solid-state contenders, and they infused images with a greater sense of dimensionality. The latter characteristic contributed to the reach-out-and-touch-it quality of the sound produced by these amps, which resulted in a heightened sense of realism. The SixPacs also had a decidedly more natural midrange and treble presentation than the Coda 12.0, which sounded cool and lean in comparison.

Although I’ve admired the Simaudio Moon W-5 for a long time, if I had to choose one amplifier from this group to live with for the long-term it would be a toss-up between the Blue Circle BC28 and the SixPacs. Both of these amplifiers have considerable strengths and few weaknesses, yet both provide a degree of dimensionality and tonal color, and an overall sense of musical rightness, that neither of the solid-state amplifiers in this group could equal.

Conclusion

I’ve made some poor equipment purchases over the years, and I’m not afraid to admit to them. Several years back, I bought a used Conrad-Johnson Premier 1 preamplifier that broke down so often I spent almost as much money repairing it as I did to purchase it in the first place. (In C-J’s defense, I found out that the previous owner decided to perform some DIY "improvements" that fouled things up.) Later, I spent a bundle on an all-Theta digital front-end that I soon realized had the musical soul of a paperweight and replaced it with a good vinyl rig. Why am I sharing this? So that when I tell you that the Audio Electronic Supply SixPac amps are benchmark products at their price point and must-hear amps for anyone remotely considering the purchase of a tube design, you’ll know that I’m not simply trying to hide the fact that I blew it again in order to justify my own purchase (although I’m sure I’ll have plenty of future opportunities for failure).

The Audio Electronic Supply SixPacs are a breakthrough in terms of tube-amplifier price and performance. For $2400, you get a pair of Dennis Had-designed, hand-wired, all-tube, 50W monoblocks made to Cary Audio standards and backed by the same company that stands behind the Cary Audio name. Sonically, the SixPacs are laughingly good and competitive with amplifiers that cost several times their price. To top it off, they don’t take up a lot of space, can be moved without a forklift, and can warm a small room on those cold winter nights. What else can you ask for and expect to get? I’m keeping mine.

...Andrew Chasin
andrew@soundstage.com

Audio Electronic Supply SixPacs Monoblock Amplifiers
Price:
$2400 USD per pair.
Warranty: Three years parts and labor.

Audio Electronic Supply
1020 Goodworth Dr.
Apex, NC 27539
Phone: (919) 355-0014
Fax: (919) 355-0013

Email: info@audioelectronicsupply.com
Website: www.audioelectronicsupply.com

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