September 2002

The Aria WT Series Hybrid Amplifiers
For The New Millennium
Review by Wayne Donnelly
Click here to e-mail reviewer

  Michael Elliott has been designing and building audio components for more than two decades. His best-known work has been the hybrid amplifiers -- i.e., having tube input stage and solid-state output -- produced by his former company, Counterpoint, which were prized by many audiophiles in the '80s and early '90s. After Counterpoint closed, Elliott has spent most of the '90s developing upgrades for and making repairs to his Counterpoint products. But with the founding this year of Aria Ltd., Mike's back -- with new amplifiers that, while faithful to his belief in hybrid circuits, are innovative and thoroughly leading-edge in performance.

For any audiophile who has witnessed -- or participated in -- the eternal debate over tubes vs. transistors, the theoretical appeal of a hybrid amplifier is obvious. The warmth, fully fleshed-out harmonics and spatial dimensionality typically attributed to tubes, in tandem with the more powerful and controlled bass and dynamics commonly associated with the very low output impedances of good solid-state output stages can be beneficially combined. And because small-signal triodes such as the 6SN7s used here normally last four years, and there are no power tubes requiring periodic replacement, the hybrid approach promises a more economical long-term operating life than a pure tube amplifier. To realize this potential requires design and engineering that truly bring together the best qualities of each technology.

The Aria Whole Tone amplifier line comprises two models: the WT 100 stereo amplifier and the WT 350 monoblocks; the respective numbers indicate rated continuous output power into eight ohms. The WT 100 is convertible into a WT 350 via a single switch and reconnecting the speaker cables. This easy conversion is just one instance of the flexibility designed into the Aria line. It provides an easy upgrade path for any owner who may ultimately want the higher output power but is initially budget-limited. While the additional switching circuitry may be presumed to have some slight effect on the sound of the bridged amplifier compared to a straight WT 350, Michael Elliott asserts that the difference is extremely small. Moreover, a WT 350 cannot be down converted to a WT 100. Because I planned to review both amplifiers, Aria provided two WT 100s bridged for initial monoblock use.

There are two classes of WT amplifiers: LS (low-sensitivity) and HS (high-sensitivity). The LS models have 17dB of gain, and are designed for use with high-output (minimum of 4 V) pre-amplifiers, including most tube designs. LS amplifiers have a bandwidth from 1Hz to 125kHz. HS amplifiers require only 0.6 V output from the preamplifier; this lower value is typical of solid-state pre-amplifiers. For this review, I drove LS amplifiers with my tubed Thor TA-1000 line stage.

In addition to the standard WT amplifiers discussed here, Aria also produces other versions, which are architecturally identical but made with premium cost-no-object parts - at a premium price. Regrettably, I have not auditioned the XL amplifiers.

Internal Architecture

Upon removing the front grille of the enclosure, one immediately sees the two Sovtek 6SN7 input tubes, nestled into excellent ceramic gold-contact tube sockets. Behind them to the left the large power supply capacitors are visible. The output stage (four beefy bipolar transistors per channel) is on the right. The output transistors are mounted on a substantial PC board. With the top and sides of the enclosure removed - a simple task - the logic, to elegance, economy and robustness of the entire functional architecture are evident. Very impressive design and engineering are on display here.

Exterior Architecture

The all-aluminum exterior is a distinct visual departure from the typical mini-tower amplifier. With its distinctive horizontal bars wrapping around all but the rear panel, and its subtle champagne and silver-tinted color scheme, an Aria looks remarkably like a model for an expensive building. The design is practical as well - the aluminum bars act as heat sinks, and a considerable amount of open space between the bars facilitates ventilation.

The only control visible on the front panel is the Standby/On button located in a sculpted hollow. Above the switch are LEDs - red for Standby mode, flashing blue during the 40-second stabilization interval, and solid blue to indicate full operational status.

Five hard rubber feet support the chassis, but Aria supplies threaded spikes that can be substituted for the feet. The 0.25-inch 20 threaded holes will fit many aftermarket support accessories. I had excellent results, for instance, with the cones that came with my Polycrystal amplifier stands. Again, you get flexible choices.

The main power rocker switch and all connections are on the lower part of the narrow rear panel: IEC socket, high-grade RCA and XLR inputs, and four sets of Cardas binding posts to facilitate bi-wiring. Shorting plugs for the XLR jacks are supplied to eliminate open circuit noise when the RCA inputs are in use. Those plugs are not just a frill - at one point I began hearing a pronounced hum from one amplifier, and after much switching of interconnects and moving of power cords, I finally discovered that someone -- although all candidates denied culpability -- had for some obscure reason removed the shorting plugs. After reinserting them I heard no more hum and the amplifiers were again dead quiet.

The connections are clearly identified, and their tight grouping reflects the designer's concern for direct connectivity and short signal paths. In practice, however, this layout can be problematical. The RCA input jacks are directly underneath the outer speaker binding posts, and the XLR inputs are right under the inner sets of posts. Owners who favor thick, inflexible interconnect and speaker cables may have trouble making some connections.

For example, when I was using Transparent Reference XL interconnects and speaker cables -- which are an excellent sonic match to the Arias -- I had to bring in the speaker cables at a 45 degree angle to make room for the interconnect. Because the speaker posts are very close together, one must be careful not to short the positive and negative spade lugs. Although I tried to be careful, I still managed once to short out one channel, blowing the speaker fuse. Replacing that fuse is not a trivial task, as the fuses are located deep in the amplifier rather than in accessible sockets on the rear. If you want to use bulky wires with the Arias, putting good single banana plugs on the loudspeaker cables might make things easier. I had no trouble, however, with the thinner and more flexible cables from Nordost, Townshend and Kimber that also saw duty.

Fine-Tuning The Aria'S Voice

After several conversations with Michael Elliott, I began to understand that he sees his amplifier as a kind of sonic tabula rasa -- a high-resolution, very neutral circuit that is highly susceptible to fine tuning to suit the customer's preferences. For example, a plain industrial-grade power cord comes with each amplifier, but Elliott encourages his customers to try premium power cords. I tried four different ones, and they all sounded better than the supplied cord.

More important yet is the choice of tubes. The original equipment input tubes -- two in the WT 100, one in the WT 350 -- are the readily available and decent-sounding Sovtek 6SN7's. But when Michael Elliott came to set up the amplifiers, he brought along four different varieties of NOS 6SN7 -- from Telefunken, Sylvania, GE, and the eventual winner in the tube-rolling shootout, vintage RCA/National 6SN7GT's. All of the candidates had strong points -- one more dimensional, another with more extended bass, etc. -- but the RCA's were magical in the Arias, having superb inner detail, rich harmonics and beautifully balanced dynamics from top to bottom. They simply drew me more quickly and completely into the music than the others.

Mindful of the obligation to review the standard product, I did at one point reinstall the Sovtek tubes for a few days. I could find little fault with them in the left-brain checklist kind of evaluation. They were nicely extended, very quiet and quite satisfying to listen to -- if I had not gotten used to the gorgeous sounds delivered by the NOS RCA/Nationals. The conclusion I drew from this experience -- and from the numerous substitutions of interconnects and speaker cables over the weeks -- is that Elliott has indeed created an extremely neutral amplifier circuit. The sound of the Arias is chameleon-like, it's hue shifting subtly according to source components, wires and, especially, the sound of the input tubes.

There is yet another factor in the Aria sound, which I have not previously encountered in any solid-state equipment. Michael Elliott explained the concept very lucidly in an e-mail to me, and rather than paraphrase, I give you his words:

"I wanted to bring up something that I may have made mention of before: the amplifier's ' voice,' or ' tonal center.' The WT amps are unique in that there is a way to change their tonal balance in a range from romantically warm and soft at one extreme, to light, detailed and very fast at the other --and points in between. Technically speaking, this tuning of the amplifier's voice can be accomplished by making very small adjustments to the values of some emitter resistors in the pre-driver stage, along with compensating adjustments of biasing.

The 'factory' or baseline setting for the WT amplifiers exposes my personal bias in matters of sound, favoring weight, richness and liquidity perhaps over detail, air and speed. I like detail and air, but not at the expense of liquidity. It's very much a balancing act, one that has taken a few years to fine-tune. And the great majority of clients have been very happy with it. This is how the amplifiers you are reviewing are set.

In some cases, however, a client has a strong preference in sonic presentation that differs from my reference voicing, or a system that leans heavily in one direction and wants some compensation. Some guys like a fast, electrostatically transparent sound, and I do accommodate them. Others (usually with their wives agreeing so strongly that you can almost 'hear' them nodding their heads while hubby talks to me) want nothing to do with anything even close to edgy sound. So I voice the amp to be a bit soft 'up there.'

When installing an XL (premium) WT amplifier, I do the voicing during the onsite installation in the customer's home. For non-XL (basic) amps, I make it a point to discuss sonic preference with a customer, and in some cases, if I feel that he would be happier with an adjustment to the amplifier's voice, I make a modification here at the factory before shipping the amplifier. Either way, I always ask about sonic preferences, and let the client know about custom voicing.

So you see, the character of the amplifiers is not set in stone; voicing is very much part of what I offer, something I enjoy being able to offer. Heck, in two cases I even took the amps back and tweaked them some more to make them perfect for the client. I feel that hi-fi offers (or at least it should offer) enthusiasts the opportunity to have their systems sound the way they want them to sound."

During the monoblock phase of the review period, the amplifiers had the standard voicing. Later, as I evaluated them as 100 WPC stereo amplifiers, Michael Elliott did re-voice one of the WT 100s; I'll discuss the differences later in this article.

Review Setup

Throughout the review process, the analog front-end was my Basis 2800/Graham 2.2 with a van den Hul Black Beauty moving-coil cartridge. Digital sources were much-modified Sony SCD 777 ES (SACD) and Pioneer 434 DVD/CD players. The preamplifiers were the tubed Thor TA-1000 line stage and TA-3000 phono stage. The loudspeakers for the monobloc phase were Bybee-modified Eggleston Andras.

The Thor preamplifiers and the Low-Sensitivity Aria amplifiers proved to be a great match, delivering a tonally gorgeous, excitingly dynamic and spacious sound. I do regret that I did not have on hand a fully balanced preamplifier, as I could not compare the sound of the Arias -- a fully balanced differential design -- with balanced vs. single-ended inputs. Theoretically, a balanced configuration might yield even better sound.

Another somewhat unusual issue with the Arias was the need to attach Zobel networks between positive and negative loudspeaker terminals. The Zobel,, which incorporates a capacitor and a resistor, looks like a small jumper. The typical reason for using one is a combination of very high bandwidth in the amplifier and high capacitance in the speaker cable.

Michael Elliott explained to me that speaker cables constructed for very low inductance often have correspondingly high capacitance. Wide-bandwidth amplifier output stages (the no-negative-feedback Aria output stages go out past 10 MHz) can be affected by such cables, because at those high frequencies the cable acts more like a badly terminated transmission line. A transmission line delivers all its energy into the load when the load impedance matches the characteristic impedance of the transmission line. If there is a substantial impedance mismatch, a portion of the energy is reflected back to the sending end.

Loudspeaker impedances are not at all similar to the characteristic impedance of a high-capacitance low-a the inductance cable, so energy (typically around 1MHz) gets bounced back to the amplifier. Because the amplifier is active at this high frequency, it reflects the energy back out again. Back and forth, bouncing from end to end, growing in amplitude -- sometimes thousands of times greater -- with each bounce. The Zobel network alleviates the problem by presenting a resonance-damping load to the cable.

The presence of this resonance phenomenon with the Aria is signaled by a pronounced hiss or buzz, a clear departure from the amplifier's normally dead quiet operation. There was no hiss with the Transparent Reference XL speaker cable, but it did occur with both the Nordost SPM and Townshend Isolda cables. With both of the latter, the installation of the Zobels cured the problem.

Listening To Monoblocks

High-current amplifiers with 350 WPC would seem to be a luxurious amount of power for most home audio systems. But I am used to such abundance. My VTL MB-750 tube monoblocks equal the and WT 350s' output in their lower-power triode setting, and more than double that in tetrode mode. Over the years I have learned that the Eggleston Andras, nominally 87 dB sensitive, make their best music when driven by big, powerful amplifiers. So the Arias had a high standard of performance to measure up to.

Measure up they do, and without breaking a sweat. Laura Nyro's intimate vocals and piano on her late recording Laura Nyro Live: The Loom's Desire beg that old "right there in the room" cliché. My current favorite soprano, Renee Fleming, raises the requisites number of goosebumps as she soars through Richard Strauss's Four Last Songs, as does the huge dramatic voice of Jessye Norman in the same music. On the male side, Dave Alvin's weathered voice and the rowdy energy of the crowd interacting with his band The Guilty Men (love that name!) are an instant party when I slap Out in California into the player.

That old audio bugaboo, a classical piano? Nojima's near-subterranean left hand chords in Ravel's Gaspard de la nuit have never sounded better -- colorful, resonant and perfectly controlled. Orchestral music? How about the closing "Appian Way" movement of Respighi's Pines of Rome (Reiner/CSO) and the great Dorati/LSO Firebird, both in single-sided 45 RPM Classic Records reissues? If I were to gas out the Arias, these two amp-killers would do the job. But the Aria monoblocs sail through the awesome dynamic demands and illuminate the fantastic orchestral color of both pieces.

In their combination of delicacy and power, their tight grip on the Andras, the Aria monoblocks seem to synthesize the best qualities of both the triode and tetrode modes of my VTLs. They sound like fine push-pull triode amplifiers with a much better than expected damping factor. Soundscaping is a bit less luxuriant in width and depth than I hear from all glowing glass, but still excellent, with superior image placement and stability.

Listening to the WT 100 Stereo Amplifier

As we might expect, a single stereo WT 1000 has a sonic profile nearly identical to the Aria monoblock sound. At least that holds true for low to moderately loud listening levels. When I crank the volume to health-endangering levels, as happens from time to time, the more limited headroom becomes noticeable. Most noticeably with the Respighi and Stravinsky records, I hear not clipping per se, but a slight degree of dynamic flattening, especially in massed brass passages. The stereo amplifier also seems to have less grip, less authority with the hard-to-drive Egglestons. Although these relative shortcomings are subtle -- and almost certainly system-related -- the overall effect is that my listening sessions are less relaxed, and I am more conscious of listening through the system. I believe, however, that the WT 100 will do a terrific job in systems that do not need multi-hundred-watt power.

While listening to one stereo amplifier, I sent the second amplifier back to Aria for re-voicing. Michael Elliott's assignment was to shift the tonal center toward the "yin" -- i.e., more warmth and bass "bloom," and a more relaxed top end. What I was shooting for was a sonic profile reminiscent of the $20,000 WAVAC EC-300B, which I recently named as a "Best of the Year" amplifier -- a fast, not overly soft single-ended triode.

While he had the amplifier for re-voicing, Michael Elliott phoned me with another option. He had found a new brand of coupling capacitor, the DYNAMICAP, which he thought was better than the Audience Auricaps he had been using until then. Was I interested in hearing the new coupling capacitors? I was, of course, but I felt that this change would make it difficult to fairly evaluate the re-voicing. To solve this problem, Elliott rigged two toggle switches on the front of the amplifier which would enable me to switch between the two types of capacitors.

Listening to the re-voiced WT 100 quickly put a smile on my face. The bass now had a richer but still beautifully defined quality, and the female voices took on a shade more warmth and "flesh"-- just what I was looking for. After a couple of days, I threw the toggles and brought the DYNAMICAPS into play. Not a huge difference, but definitely audible -- and worthwhile. Primarily, the sound seemed more relaxed, more liquid with the new capacitors.

Thanks to fortuitous timing, I have been able to listen to the re-voiced and improved WT 100 not only on the Egglestons, but also on the Von Schweikert dB-99s (a smaller sibling to the dB-100previously reviewed in this magazine -- review in progress). These 99 dB-sensitive loudspeakers with internal 400-watt bass amplifiers, designed for low-power SETs, make no power demands on the Aria. But he voicing change is equally effective under these conditions. If I close my eyes, I hear glorious tube sound.

I also tried the Aria with the new Meadowlark Swifts. Those adorable little $995/pair, 89dB floorstanders are an unlikely match pricewise for the Aria, but the combination is pure delight -- boogie all night long!

Conclusions

I began this review by proposing that superior design and engineering would be essential to realizing the sonic potential of the hybrid concept. Clearly Michael Elliott has more than met the challenge. The WT amplifiers are a tour de force -- visually distinctive, and capable of many shades of "tube-like" sound without the ongoing cost and maintenance associated with power tubes. DC to 120kHz bandwidth, 100 to 350 watts of high-current power that increases substantially into four ohms, with stability down to two ohms. I fairly salivate just thinking of how the premium XL versions must sound.

These amplifiers are not inexpensive. But considering their superb build quality, engineering finesse and uniquely fine-tunable sound, the factory-direct prices are not just a value but a bargain. Sold through retail dealers they would cost thousands more. If you're shopping for an amplifier, you might want to give Michael Elliott a call.

NOTE: The following numerical ratings are based on the Aria amplifiers in monoblock form. There would be very little difference for either the standard-voiced or re-voiced WT 100 stereo amplifier; the audible differences I heard are more right-brain (i.e., intuitive, emotional) than left-brain (quantitative, objective) in nature.

Note: Click here to read our exclusive article to learn more about Michael Elliott and his products.

Specifications

WT100 Amplifier to its Specifications
Output Power
8 ohms: 100W
4 ohms: 200W
Input Sensitivity
RCA inputs to 1W/8 ohm: 400mVrms (LS); 60mVrms (HS)XLR inputs to 1W/8 ohm: 200mVrms per signal phase (LS), 30mVrms per signal phase (HS)
RCA inputs to rated power: 4Vrms (LS); 0.6Vrms (HS)XLR inputs to rated power: 2Vrms per signal phase (LS); 300mVrms per signal phase (HS)
Frequency Response
1Hz to 120kHz (LS); 1Hz to 30Khz (HS)
Signal-to-Noise
Reference to 1W: 96dB (LS); 90dB (HS)Residual Hum and Noise: nuVrms (LS), nuVrms (HS),
Damping Factor
Ref 8 ohm: 44
Maximum Output Current
100A
DC Offset
Less than 10mV, typical. 
Power Requirements
Standby: less if than 50W, Operate 80W
Available Voltages
The WT100 can be ordered to operate in 120VAC, 220VAC and 240VAC environments. Detachable IEC Mains receptacle accepts all power cords. Unless other arrangements have been made, units destined for sale in 120V countries will be shipped with standard-grade AC Mains cord. Units destined for other countries will not be shipped with a Mains cord. All Aria products are built to meet or exceed UL/CSA safetly standards. 
Dimensions (W x L x H)
Amplifier Only: 8'' x 17'' x 13'', 20.3cm x 43cm x 33cm Shipping Crate: 11.5'' x 20-1/2'' x 19'', 30cm x 52cm x 48cm 
Weight
Amplifier Only: 50lbs, 23kgShipping Weight: 70lbs, 32kg 


Terms: 30-day trial; amplifiers returnable within that period for full refund
Warranty: Lifetime, fully transferable
WT 100 and WT 350 Amplifier Model Numbers and Factory-Direct Pricing

WT100LS -- Basic Low Sensitivity Version $4,499
WT100HS -- Basic High Sensitivity Version $4,499
WT350LS -- Basic Low Sensitivity Version $8,799 (pair)
WT350HS - Basic High Sensitivity Version $8,799 (pair)

Company Information

Aria Ltd. 
914 South Santa Fe Avenue
Vista, CA 92084

Voice: (760) 945-0356
Fax: (760) 945 0219
E-mail: info@ariaaudio.com
Website: www.ariaaudio.com