Single Ended Tube Power Amps
de Havilland Aries 845
The de Havilland lineup of single ended tube amps has now expanded, the original Aries 572 (reviewed previously, see below) now being joined by two other models, the Aries 845 reviewed here and the GM70. The 845 builds upon the strengths of the original 572, and is an even better amplifier in virtually all sonic aspects. The 845 will be the best choice for many single ended tube amp fans. At $6000 per monoblock pair, it costs the same as today's price of the earlier 572 model that it now betters in performance, yet not nearly so much as the newest and most expensive de Havilland amp, the custom GM70 at $10,000 per pair.
It's no secret that tube amp aficionados enjoy listening to the sonic differences among various tube types. The type, brand, and even production run of a tube can make a significant difference in the sonic performance of most tube amplifiers. This is especially noticeable in single ended tube amps with little or no overall loop feedback. Here the transfer characteristic and sonic performance of each tube is laid bare, more than in other circuit topologies, because there are fewer circuit tricks or mechanisms in place to hide or compensate for tube performance (e.g. no negative feedback to linearize the circuit, no balancing to cancel even order distortion, etc.). Small wonder then that single ended tube amps provide such a fertile ground for experimentation with various tube types, in order to obtain various sonic results.
The chief design engineer for de Havilland, Kara Chaffee, has boldly taken up the challenge of exploring the sonic virtues of various tubes. The three models in the de Havilland range each feature a different type of output tube, each with its own unique sonic characteristics. But each of these output tubes has very different electrical characteristics, and needs to be driven in a different way by a different circuit, if the optimum performance capability of each tube type is to be realized. Moreover, the sonic personalities of each of the three different output tubes are best complemented by input and driver stages that themselves have different sonic personalities, each optimally matched to the chosen output tube. Thus it is that Kara has taken on the heroic task of developing three different power amp circuits, each optimized for a different single ended triode output tube. And each different circuit also has been engineered with totally different input and driver tubes, chosen to best complement the electrical and sonic needs of the designated output tube.
Complementing the 845 output tube in the Aries 845 amp are the 6AV5 as a driver tube and as an input tube the 6SN7, which is famous for its natural musicality and effortless transparency when used at line level (as in preamps). The 845 output tube itself is a giant transmitting type tube, and fits into a very special type of keyed socket (with ceramic mounting insulators, and with giant claws to grasp the tube pins, and featuring air, the best sounding dielectric of all, as the primary dielectric between socket pins).
Like the other de Havilland amps, the 845 amp features point to point wiring for superior sonics, heavy duty construction and high quality parts where it counts (including expensive Electra-Print transformers, which get most of the credit for this amp's hefty 57 pound weight per channel) -- and a minimum of flashy superficial frills where it doesn't count.
The sonics of the 845 de Havilland excel over the sonics of their earlier 572 model in nearly all aspects. It sounds slightly more liquid, and so is more musically beguiling. But this liquidity does not bring with it a dark or excessively syrupy sound as in many other SET power amps. Instead, the 845 de Havilland sounds remarkably clear, vibrant, and alive, even more so than the 572.
The 845 penetrates deeper into the musical texture, and is even better than the 572 at revealing music's subtle inner details, especially throughout the midranges (a typical strong region of the spectrum for SET amps). Some of the credit for this superb musical revelation goes the fact that this 845 amp is highly linear without feedback, and then eschews the use of overall loop feedback. In testing the de Havilland 572 amp with adjustable feedback, we found that we strongly preferred the zero feedback setting, which provided the best, most open and naturally airy sound (the sound became artificially closed in as soon as some feedback was applied).
Further helping this amp's musical revelation is the fact that the 845 de Havilland sounds even cleaner and purer than the 572, which in turn sounded cleaner than most other SET power amps of its day when it was introduced. The 845 allows you enjoy the music without a haze of grundgy or juicy distortion coming along for the ride, as it does with most of the lesser SET power amps. You simply hear more of the music when you are less distracted by hearing distortion.
The clean, pure sound that this 845 amp achieves, even without any overall feedback to lower distortion, is also a tribute to Kara Chaffee's design work and to the inherent linearity for the whole circuit that Kara has achieved.
When an amp excels at revealing music's subtle inner details, as the 845 does, then it naturally also excels at stereo imaging, since the subtle imaging cues that make an image truly believable are themselves inner musical details embedded in a good recording. The 845 amp excels at projecting dynamic music in a tactile, coherent way that makes you believe you can reach out and touch the musicians.
The de Havilland 845 is rated at 25 watts output, which is less than the 572's 35-40 watts, but the 845 amp actually sounds more dynamic, more punchy, more capable of generating musical loudness without fatigue creeping in to set a ceiling.
The 845 continues the de Havilland tradition of handling the frequency extremes much better than most other SET power amps. In the trebles most other SET power amps turn fuzzy soft, veiled, and defocused, with grundgy distortion making treble definition even worse. The de Havilland 845 has none of these problems, and handles trebles with very good cleanliness and focus. There is just a slight rounding of treble transients, but for many listeners this will fit consistently with this amp's liquidity, certainly better than an etched treble sound would.
In the bass, most other SET power amps turn flabby, loose, boomy, and muddy. The de Havilland 845 has much better bass definition than most other SET power amps, without any loose flab or ill defined boomy heaviness. The low bass might not have the sheer impact that the best push-pull amps can achieve, but the 845's tight bass definition is a notable performance for an SET power amp.
An SET power amp tends to have a higher source impedance than most push-pull and solid state power amps, especially when as in the case of the de Havilland 845 there is no overall loop feedback. This means that the impedance curve of the speaker system you're using will inevitably slightly affect the final tonal balance of the power amp when driving that speaker system. This simple interaction with speaker systems could in itself produce some rounding in the trebles we heard, as well as different bass sonics. So you might hear even better performance than we did from the de Havilland 845 at the frequency extremes, depending on the impedance curve characteristics of your chosen speaker system.
Likewise, the midrange tonal balance could be affected by the speaker's impedance curve. We heard the 845's outstanding clarity and dynamics being brought to the fore by a slight tonal emphasis in the upper midrange, but on your speaker system this might not happen. We can assure you, though, that the 845 is not a shy, polite, retiring amp that's all warm and mellow, dark and syrupy. This amp has moxie, and brings you the music full of life.
When de Havilland introduced the Aries 572, their first amp, a couple of years ago, there were many SET power amps on the market, but their performance was pretty sad on the whole, with limited power, limited bandwidth, and high audible distortion. The 572 bettered the performance of most of these other SET power amps, and itself was only bested by SET power amps costing far more money (see our previously published review of the 572, below).
Since the 572's introduction, the competition has come out with new, good sounding SET power amps, some at reasonable prices, which give the 572 a run for its money. But de Havilland has not rested on its laurels in this interim. Their newer models, the Aries 845 reviewed here, and we presume the more expensive GM70 as well, give you even better sound than the Aries 572 (and the 845 costs no more than the 572 now does ). So de Havilland continues to be a value leader, giving you more of what an SET power amp should do, for a reasonable cost. Keep up the good work, Kara.
de Havilland Aries 572 (this review published previously)
Most other single ended tube power amps can only dream of performance like this. The de Havilland Aries actually delivers. And it delivers at a price far less than other SET amps with equivalent performance. The Aries sells for $3995 per monoblock pair, directly from the factory [now $6000]. The only other SET power amps we judge to have comparable sonics are the recent Cary 1610-SE at $39,995 (10 times the price) and the Venture Reference One at $24,000 (6 times the price).
Freedom to Choose the Best Speakers
The de Havilland's most astonishing feature (and its most useful) is its power, 40 watts per monoblock channel. Not 3 watts, or 5 watts, or 8 watts, or 12 watts like most other SET amplifiers. That 40 watts is a pretty amazing achievement for a single ended class A triode amp. It wasn't all that many years ago that the most powerful amps you could buy at any price put only 40 watts per channel (e.g. the Marantz 2, 5, and 8B), and those amps achieved their power using the far more power efficient topologies of push-pull instead of single ended, class AB instead of class A, and pentode instead of triode output tube.
That 40 watts of power puts the de Havilland in a whole other league than most other SET amps, since that's 10 times the power of most. That dramatic margin of power is vitally important for better sound. Note that we said important for better sound, not merely important for louder sound. Why? The usefulness, the significance of this enormous extra power is not merely additional loudness. It is freedom. Freedom, and neutrality, and accuracy, and bandwidth. Freedom to choose a better loudspeaker. Freedom to choose a loudspeaker that is more neutral and more accurate and with wider bandwidth.
Most other SET amps, with only the usual 3 to 8 watts, restrict your choice of speakers to only the most efficient. This is a very restricted, narrow choice, since the vast majority of speakers have only moderate to low efficiency, and they are unusable if your amp puts out only 3 to 8 watts. Since the speaker is the least perfect link in your chain, it is the most important link for you to make as good as you can. So naturally you'd want to be able to choose from as wide a selection as possible, not just a limited selection. Moreover, the laws of physics pretty much dictate that very high efficiency speakers are less neutral with worse tonal colorations, and have less flat frequency response within their bandwidth, and have a less wide bandwidth, and have worse colorations from time ringing material resonances, and have poorer stereo imaging. For example, speaker designers can reduce undesirable diaphragm resonances by making a diaphragm thicker and heavier, or by adding damping material that also makes it heavier. But adding weight reduces speaker efficiency, so the most efficient speakers need to keep their diaphragms light, and thus they tend to have worse diaphragm resonances. Also for example, high overall speaker efficiency requires high efficiency in the bass, which requires a large cabinet, which usually means a large front panel area, which degrades stereo imaging (unless the system uses modular enclosures).
If your power amp's output is so miniscule that it forces you to select an inferior choice for the weakest link in your chain, the speaker, then the degradations you suffer from having to use an inferior speaker will more than offset any gains from using a slightly better sounding amp -- especially given the fact that amps are one of the stronger links in the chain. The amount to be gained from using a better amp is likely to be much less significant than the amount to be lost from using an inferior speaker, so SET amps with miniscule power output compromise your overall system, regardless of how good the amp itself might intrinsically sound.
The de Havilland's 40 watts free you to choose almost any speaker you want, including the finest, most accurate, most neutral, best sounding ones -- and still have that special SET sound to combine with the speaker of your choice.
Facing SET Challenges:
Besides limited power output, there are several other challenges that SET power amps must deal with, and here too the de Havilland surpasses most.
Consider the challenge of distortion. The de Havilland sounds much cleaner and purer than most other SET power amps, so that we can enjoy and focus on the music, without the annoying distraction of distortion artifacts. Most other SET power amps exhibit easily audible distortion, often sounding like a dirty grundge through the midranges, a fuzzy smear in the trebles, and boomy sounding harmonics in the bass. SET power amp circuits do not have the distortion canceling benefits of balanced or push-pull topologies (which inherently cancel even order distortions), and various other factors (e.g. having to push large currents through transformers) conspire to worsen other various distortion mechanisms. We have openly criticized many SET power amps for having objectionably high levels of readily audible distortion (e.g. the older Cary models, and most SET amps using 300B tubes). We hear their distortion front and center stage, which in our view negates whatever tonal charms these amps may bestow upon music with their romantic midrange bloom. The de Havilland deserves great praise for conquering this SET distortion bugaboo, where so many others have failed.
Two factors deserve special mention, for helping the de Havilland to achieve audibly lower distortion than most other SET power amps.
The first factor is, again, power. The de Havilland's dramatic margin of 10 times more power has a byproduct of achieving lower distortion at ordinary listening levels, from a triode output stage.
Why is that? Let's follow a chain of reasoning over a few paragraphs. Firstly, even though triodes are less powerful than other tubes as output tubes, triodes are desirable because their transfer (amplifying) characteristic is inherently linear, so they can be used with little or no negative feedback, whereas other types of output tubes (tetrodes and pentodes) are inherently less linear, so they require more negative feedback.
But there are complications. A triode's transfer characteristic is truly linear (straight) only for a portion of its operating range, and beyond that it gently curves in a nonlinear (non straight) fashion. Tetrode and pentode output tubes, are made linear by feedback, up to the point of clipping, at which point the sound usually turns so ugly that every listener is instantly warned to back off on the volume control, the result being that tetrode and pentode output tubes are usually not listened to in their nonlinear regions, and are heard only in their linear regions (as created by feedback); since tetrode and pentode tubes can put out plenty of power, there is usually no rationale for pushing them into their ugly sounding clipping region. In stark contrast, triodes are often listened to in their nonlinear regions. Because the triode's transfer characteristic curves gently outside its linear region, there is no sudden onset of ugly sounding clipping. Instead, the sound simply starts becoming slightly dirty, grundgy, and fuzzy -- imperceptibly so at first, then gradually more and more noticeably as the music gets louder.
Many listeners (especially those accustomed to vinyl's distortions on louder music passages) don't key in on this distortion that occurs during louder music peaks or passages, so they typically run their SET power amps well into the curved region of the triode's transfer characteristic, so these listeners are actually listening to their SET power amps producing a lot of distortion.
Now we get to the key point in this chain of reasoning. These listeners don't really have much choice anyway. Given the miniscule 3 to 8 watt power output of most SET amps, most listeners have to run their amps into the curved nonlinear region just to get a reasonable normal listening level out of most any speaker (save a fully front loaded horn system). On the other hand, an amp such as the de Havilland, with 10 times the power, affords the listener the unique luxury of being able to achieve normal listening levels while still keeping the triode output tube within the ideal linear (straight) region of its transfer characteristic. In sum, the de Havilland has the headroom to allow you to hear a triode in its ideal linear region, with lower distortion; most other SET amps do not.
The second factor is the engineering by the de Havilland's designer, Kara Chaffee. Kara has developed some unique circuitry to give this amp extra headroom and lower distortion (and wider bandwidth as well). And Kara has also provided generous margins of headroom in the circuit parameters and in the parts chosen for the circuit. For example, the driver tube, that is merely used to drive the output tube actually supplying the power, is a KT88/6550. Note that this tube is so robust and powerful that it is usually used as an output tube for 60 watt amplifiers. And here in the de Havilland this tube is being used merely to drive another output tube putting out merely 40 watts. By the way, the triode output tube itself in the de Havilland is an SV572.
(Continued on page 46)