The deHavilland Aries 845-G SE Monoblock Power Amplifier
By Dick Olsher
The Gentle Giant
Its presence commands attention. Peering through the glass envelope is a massive anode machined out of a solid block of graphite and rated up to 100 watt dissipation. Power it on, and its directly heated thoriated-tungsten filament gives off a white hot glow. Dinosaur-sized relative to post World War II miniatures, the 845 was released by RCA in 1931 as an audio-frequency amplifier and modulator tube, and saw extensive use in RCA AM radio transmitters. Eric Barbour points out (Vacuum tube Valley, Issue #9) that many of these old RCA transmitters were pressed into service by small local broadcasters in the late 40s and 50s. Quoting Eric: "Millions of Americans were exposed to R&B and gospel music via the smooth sounds of push-pull 845s, driven by interstage transformers, with no negative feedback."
The 845's low amplification factor, relative to its cousin the 211, discouraged its use for audio applications during the 30s and 40s. Difficult to drive and demanding high plate voltages on the order of 1,000 V, the 845 was only kept in production to keep old AM transmitters re-tubed. Today the only inexpensive source for new production 845s is China. And so the gentle giant went into slumber for some 30 years, only to be awoken during the 80s in Asia. Underground audio interest in directly heated triodes (DHT) reached a fever pitch. In particular, the 211 and 845 began to command considerable attention because of their extremely linear transfer characteristics, and ability to deliver significant power in single-ended operation. DHT practically became the banner of a new religious order in Japan. The Audio Note Ongaku, based on the 211, made quite a splash in the USA in the 90s, and despite its ridiculous price tag, I too walked away impressed with its sonic magic.
The deHavilland Aries 845
This amplifier is about clean SE power. In the words of Chief Engineer, Kara Chaffee, "It was our goal to build a SE amplifier that would drive medium efficiency , as well as high efficiency loudspeakers, and still deliver the midrange magic that SE is justly famous for. Much of the R&D was done using a pair of B&W 805 minimonitors, which are about 86 dB efficient. Many non-horn type speakers are 90dB efficient or greater, and the Aries- 845 drives them beautifully. As the Aries design matured, we ourselves were impressed that the amp sounds like a much bigger amplifier than the numbers would suggest . There is something very important about the quality of the watts, that gives the music a free and dynamic quality, having less to do with the maximum power output, than you might imagine." Chaffee gradually came around to like the sound of SE amplifiers after experimenting with big triode push-pull designs. She notes the immediacy of the sound plus the ability to relax and just enjoy the music. The latter quality is captured by the phrase "kick off the shoes" in front of an audio system. Ironically, and as Chaffee points out, that is not an attribute that shows up on an audiophile's checklist. In other words, there are amplifiers out there with better bass, more extended highs, more power, lower distortion, more watts per dollar, lower weight, more efficient, etc. But when it comes to the sheer enjoyment of music, a good SE amplifier is impossible to beat.
Chaffee built her first tube amp from scratch at age 13 and found the inspiration to tinker with electrical and mechanical things from her father. She gradually discovered that SE magic correlates with lack of global feedback. And without feedback you're stuck with the basic character of the tube. It then became a matter of "endless experimentation to find the right mix of tubes and passive components." She also favors simple circuit topology implemented with high quality transformers and components. The following quote should be mandatory reading for anyone contemplating an expensive SE amplifier purchase: "I do not believe in the idea that you have to spend thousands of dollars to get first rate sound. I would not have any idea of how to put $35,000 into an amplifier and not mess it up. I mean you can only use just so many resistors and capacitors!"
The output stage uses a single 845 in a standard SE connection with the plate circuit coupled to the primary winding of an Electra Print output transformer. The output stage operates in fixed bias with a nominal plate current of 60 mA. A bias meter and pot allow manual adjustment of the plate current. The bias meter senses the voltage across a 10-ohm resistor in the cathode circuit. Therefore, a hand-held volt-ohm meter (VOM), set to DC volts may also be used at the test points for adjusting the bias. A 60 mA current through a 10-ohm resistor equates to a voltage drop of 0.6 V. You may then tweak the pot to read either 6 on the built-in meter or 0.6 V on an external VOM. I have found the bias to be quite stable over many weeks of operation. Plan to check the bias as the 845 ages, probably every 50 hours or so of use. Note that the amp reverses polarity at the outputs. No big deal just connect the black leads of your speaker cable to the red coded output terminals. Or if the preamp also reverses polarity, then no lead reversal is necessary.
The input stage uses the venerable 6SN7 twin triode a favorite of mine and obviously of Ms. Chaffee. Just check out her email address: 6SN7@abac.com. The two sections are cascaded and DC coupled to provide sufficient voltage gain for the driver stage. My samples came outfitted with RCA 6SN7GTA/GTB types. I substituted the classic Sylvania 6SN7WGTA "chrome" top, which sounds cleaner and better focused in the context of my system. If you do experiment with your favorite 6SN7, be sure that you stick with the GTA or GTB types only as the older 6SN7GT is not rated for the higher voltages used in the Aries 845.
The driver stage is unique in a couple of respects. First, it is configured as a cathode follower, providing low output impedance and exceptional current drive. Second, it is based on the 6AU5, an early television sweep tube, which is connected as a triode for this application. Prior to mid 2002, a 6AV5 was used in this position. Having heard both versions, I can tell that there's clearly more synergy with the 6AU5; the mids being harmonically richer, more refined and dynamic. Therein lies the art of voicing. I've always thought of the 845 as harmonically less interesting than say a 300B. The harmonic palette of a 300B seemed richer, and that of the 845 somewhat bleached out by comparison. At least in previous designs, the 300B commanded my respect in regards to the midrange, while the 845 seemed like a copy of the real thing. Remarkably, that is NOT the case with the Aries 845, and it's a perfect example of how the character of the 6SN7 input and 6AU5 driver tubes compliments the basic nature of the 845.
The power supply is based around a massive and oversized power transformer that provides excellent regulation. This is in keeping with the deHavilland design philosophy. Chaffee likens a good amplifier to a pyramid, with nine tenths of the amp being power supply, and one tenth the audio circuit proper. She says: "You want the power supply wagging the audio, rather than the audio wagging the power supply." Rectification is solid state, but the diodes are "HEXFRED" types very fast and sweet sounding.
It is critical to acknowledge at the outset just how successful the Aries was in accomplishing its basic mission. Driving my BassZilla loudspeaker, Lowther version with the DX4 full range drivers, it clearly transcended ordinary listening. There has been much research on the effect of music on stress and tension. For example, neuroscientist Anne Blood at McGill University in Montreal, discovered direct evidence that music stimulates different regions of the brain responsible for memory, motor control, timing and language. Music can activate different parts of the brain, depending on what type of music you listen to. The effect on mood was studied by McCraty et al (1998), who found that grunge rock music increased hostility, sadness, tension, and fatigue, and reduced caring, relaxation, mental clarity and vigor. In contrast, 'new age' music produced the opposite effect. It has even been suggested that certain types of classical music enhance performance the so called Mozart effect. The same sort of argument can be made for audio systems. Reproduced sound that is artificial, irritating, and/or rife with odd order harmonic distortion can in fact increase stress and tension. Frankly, most high-end audiophile systems give me a headache. On the other hand, the Aries 845 with its big tone presentation and suave mids was instantly therapeutic. After a hard day at the office, this puppy will practically pour you a drink and kick off your shoes. I especially like the harmonic richness and timbre accuracy with which it portrays female voice nothing short of seductive.
Let me get back to that big tone presentation. In the lexicon of the electric guitar player, that refers to a full-bodied, gutsy lower midrange. This is the range within which the music's fundamentals reside and also happens to coincide with the power range of the orchestra. In my book, reproduced music stands or falls on the strength of the lower mids. This is where the Aries was able to construct a tactile flesh and bones reality. Hall ambience as well as an orchestra's foundation were painted with superb artistry. What made it all extra special was the clarity with which low-level detail was being resolved. Many SE amplifiers thicken harmonic textures to the point of blending detail away. The Aries allowed detail to bubble to the surface without ever being in your face about it. The decay of transients into the noise floor of the recording was extremely easy to resolve as were complex harmonies. This rare gift of a midrange that is both crystal clear and suave sounding is a case of having your cake and eating it too.
The soundstage presentation was wide and deep. Space was finely layered with an excellent feel for depth perspective. Image focus was rock stable. The palpability of image outlines was such that the sensation of being able to reach out and touch someone was very real. The magic of 3-D image outlines is one of the attributes of a good sounding 6SN7, and I'm glad to report that its character carried all the way though from the input stage.
The treble range sounded both fast and detailed. There are SE amps out there, whose bandwidth is handicapped by output transformers that struggle to make it to even 20 kHz. Such amps sound soft and soggy. In addition to sounding overly liquid, constricted bandwidth shifts stage lighting to the midrange. With the Aries you have both a big tone sound with plenty of quickness on top.
Despite its moderate output impedance, I actually liked the bass character. Bass extension and punch were very good. Though keep in mind that the actual results you obtain with any amp will depend on the quality of the front end, and in particular, that of the associated preamp. deHavilland's new line stage, the Verve (review in progress), mates tonally very well with the Aries, and is highly recommended in this context.
The Aries 845-G sounds big and powerful, adjectives that rarely go handin-hand with SE output topology. Its power reserve allows the Aries to mate with real-world moderate efficiency loudspeakers. Yet, there is plenty of SE magic to be had. There is nothing forced or artificial about its sound, which is both big tone and suave. It will most definitely relax you with its "zero harshness" presentation, but never bore you. Watch out: it coaxes a remarkable degree of detail and emotional intensity from the input signal. In my book this is one of the best sounding SE amps money can buy. And at its fair asking price it clearly represents a bargain in high-end terms. The Aries is a bane for all those trying to sell less for a lot more cash. Frankly, you'd be crazy or foolish (take your pick) to spend more money on a SE power amplifier. A five star recommendation!
Power Output: 25 watts RMS into 8 ohms
Bandwidth : 20 Hz -35 kHz
Power triode: Type 845
Driver tube : 6AV5
Input tube: 6SN7
Feedback: zero negative feedback
Input impedance: 50 kOhm (values from 10k
residual hum: <2 mV
Warm-up: automatic time delay for long
Dimensions: 12"W, 18"L, 10"H
Weight: 57 pounds
Options: Custom Elma stepped attenuators - $600
Warranty: two years on parts, one year on labor, 90 days on tubes. Warranty not
332 Alamo Square