Tip No. 20
The WAVAC Model MD-811 Integrated Amplifier
WAVAC Audio Lab clearly believes that the Force is with them. If establishment brand names such as Audio Research, Conrad-Johnson, and Jadis may be viewed as the dominant but plodding "Empire," then WAVAC strikes back with a powerful vision of what listening pleasure is all about. In particular, the Music Dandy 811 integrated amplifier combines the musical expressiveness of single-ended (SE) triodes with the real-world drive capability of radio transmitting tubes. And at a US retail price of US$3,000 it is the most affordable product in the WAVAC lineup.
Feel free to accuse me of being a neo-Cartesian, as I paraphrase Rene Descartes' famous maxim: I listen, therefore I am. Folks, the only reason I purchase audio equipment is to enjoy the music. And any gear such as the MD-811 that gets me closer to the musical experience is welcome news. My ego doesn't require a 500-wpc solid-state arc welder for self gratification. I'm perfectly happy with a few watts – providing that they inch me closer to deciphering the emotional content of the music. And as far as any technical objections you might have regarding old versus new technology, as in tubes versus transistors, remember: a bicycle speeding along at 25 mph is going just as fast as a Ferrari traveling at 25 mph.
In particular, the MD-811 features the classic RCA-designed 811A triode transmitting tube, a standard in radio communications applications since the early 1940s.This tube is still in production today as it is widely used in RF transmitters, which accounts for its extensive availability and low cost. Forget about high retubing costs: a Chinese version may be had for $13.65, while the Russian 811A is only $20.40 at Antique Electronic Supply (http://www.tubesandmore.com/). Since it was not designed for audio applications, an anode cap is used for the high voltage connection. In addition, it is a very difficult tube to drive, as it requires a large voltage swing at the grid for full output. WAVAC's solution is to use its patented IITC (Inverted Inter stage Transformer Coupling) topology, which sets apart its line of single-ended directly heated triode designs.
However, before we get to a proper description of the IITC, let's first take a quick look at the preceding stages. The input stage consists of a 12AU7A dual triode connected as a series regulated push-pull cascode (SRPP) - also known as a Mu follower. This particular topology has become very popular in the past ten years in both US and Japanese designs, though it's a bit unusual to see it at the front end of a single-ended amplifier. The signal from the SRPP stage is directly coupled to the grid of a triode-connected 6Y6 beam power pentode, which is part of the driver stage. In fact, there isn't a single coupling cap in the signal path. The IITC comes next - the brainchild of the late and legendary Nobu Shishido - whose SE designs are showcased by WAVAC Audio Lab. This transformer performs the two critical tasks of providing clean drive voltage as well as a fixed bias voltage for the grid of the 811A. The bias voltage is actually fed through the secondary of the coupling transformer, so that the audio signal rides on top of the DC bias. The output of the 811A is connected to the load through a high-quality air-gapped transformer that provides 4, 8, and 16-ohm taps. Global feedback (from the secondary of the output transformer) is used to reduce the amplifier's output impedance and improve its damping factor. The power supply uses solid-state bridge rectifiers. The grid voltage supply for the 811A is also regulated. The MD-811 is rated at a power output of 15 watts per channel (wpc) under extremely conservative operating condition for long, dependable service. The signal to noise ratio is excellent for a SE amplifier. This amp is very quiet and hum-free even when driving high-efficiency loudspeakers.
I've described the MD-811 as an integrated amp because it features three selectable line inputs and a volume control. However, tmh Audio's Jim Ricketts prefers to describe the unit as a stereo amp with a volume control. Actually, what really matters is the overall sensitivity of the amp. The voltage gain of many power amps is sufficient to handle line-level inputs without any further active gain. The sensitivity of the MD-811 is fairly low at 2 V. Thus, most CD players should do fine, but tuners and tape decks may require additional active gain. I had no trouble at all driving CD players directly into the MD-811. But note that it can be used as a stereo amp together with an active preamp such as the WAVAC PR-X1. I also expect some purists to take issue with my integrated amp label, because the unit lacks a balance control. The strictest definition of an integrated is in fact the combination of a line preamp with a power amplifier section. And a proper line preamp should include a L-R balance pot. It's a minor inconvenience in my opinion, especially when dealing with digital source material, but you should consider at least using a phono preamp with a balance control for vinyl playback.
Let me make it perfectly clear that the sonic profile I'm about to elaborate upon is not associated with the stock tube complement. In fact, tube rolling is a necessity and not an option with the MD-811. Right out of the box, its strong suites were overshadowed by so-so performance in two important areas. First, the sound was entirely too mellow. This was a first impression based partly on diminished sparkle and air through the treble, but most of all I missed more than just a few degrees centigrade of musical heat and passion. Second, the spatial infrastructure of the soundstage was constrained so that instrumental outlines failed to bloom and expand to the extent I've come to expect from world-class SE directly heated triode amplifiers. As you know, I normally don't need much encouragement when it comes to tube substitutions. In this case, Jim rickets (the US distributor) encouraged me from the start to experiment with alternative 12AU7A/ECC82 brands, as he himself obtained much better results with various New Old Stock brands. Thus began a fairly long process of experimentation. In the end I settled on the Amperex Bugle Boy brand available at the Richardson Electronics Web site for $27 each (http://catalog.rell.com/rellecom ). This is an excellent tube, being very dynamic and spatially convincing. It is a bit warmer sounding than most, but is capable of exquisite harmonic delicacy to match the sophistication of the MD-811 in this regard. The Bugle Boys certainly helped restore much needed upper octave luster and rhythmic drive, but failed to correct the above-mentioned spatial constriction. In late April of this year, I was contacted by Jim Ricketts to see if I would be interested in trying some Russian 811As, which according to his own findings appeared to possess a lower noise floor, better balance, and more dynamics than the stock Chinese tubes. Yea, sure, why not was my instant response. The Russian 811A was everything Jim indicated it would be, plus it greatly expanded the spatial bloom that was in such tight supply with the Chinese brand. Considering the cost of the substitutions I've described, the first thing that ought to be done when the amplifier is unpacked, is to jettison the stock tubes. What follows then is an outline of my long-term sonic findings based on the Russian 811A and 12AU7A Bugle Boy tube complement.
I'm not going to mince words: this is a world-class amplifier, and deservedly so for the manner in which it dispenses harmonic textures. Instrumental timbres comprise a complex mixture of harmonics with differing onset and decay characteristics. The MD-811 consistently weaved an organic musical tapestry without any electronic artifacts. It's a bit like the impression of water flowing from a tap versus the sound of a bubbling mountain stream. To my ears, tap water sounds like a solid-state imitation of that mystical mountain stream. I know that I've never confused the two. The MD-811 was relaxed and as natural sounding as only a mountain stream or the real thing can aspire to be. Individual voices were resolved with great clarity. Its level of midrange clarity is perhaps not quite the equal of its much more expensive relatives in the WAVAC family, but it succeeded very well in elucidating transient speed of attack and subtlety of decay. In other words, it captured the silence between the notes with great fidelity.
In terms of tonal balance, the spotlight was subtly but clearly focused on the midrange. The upper octaves appear to be subjectively recessed and over damped above about 3 kHz. Hence, it shouldn't surprise anyone that the MD-811 preferred to be mated with bright sounding speakers. I used it in some of my voicing tests of the BassZilla - a new high-efficiency loudspeaker kit currently under development for use with low-power tube amplifiers. Mated with the MD-811, the BassZilla's upper octaves could be equalized a full 3 dB above flat and still sound reasonably inoffensive. Also, cone breakup modes sounded more benign through the MD-811. It would therefore appear to be an ideal match for Lowther based full-range designs, providing an antidote if you will to the Lowther driver's upper octave resonances. This highlights the critical importance of the loudspeaker-amplifier interface. We often talk freely about the merits of a particular amplifier forgetting that its performance is inexorably linked to the context of a particular load.
The weakest component in the MD-811's sonic portfolio was the bass range, especially the deep and mid bass bands. Deep bass extension was fine as was pitch definition. But the bass lacked the tight control and drive, for example, of the less expensive Manley Labs Stingray integrated amp, and also fell behind the standard set by inexpensive SE triode designs such as the Antique Sound Lab KI15-Fox. The best I can do in the case of the MD-811 is praise it faintly by saying that its control of bass lines is merely OK as far as the performance bar set by most SE triode designs. If you're a bass freak, the MD-811 is bound to disappoint. I for one, found it possible to accept its bass limitations, especially in view of its extraordinary midrange magic. You just don't walk away from such a large slice of heaven!
Despite its modest power rating, the Music Dandy managed to sound like a very powerful amplifier. This is a characteristic shared by most SE triode designs, as their distortion spectrum changes very slowly as they approach clipping. They are, in general, much more forgiving about being driven hard then are push-pull designs. With a high-efficiency load, the MD-811 never disappointed in terms of power reserve. It could generate plenty of dynamics when going from soft to loud.
One of the joys of life is to experience a soundstage through the fish-eye lens of a superb SE triode amp. The MD-811 certainly didn't disappoint in this regard. Space expanded to fill the front of the listening room. It felt just like cinemascope did when I first experienced it at the movies as a small child. The Gestalt of being there is greatly enhanced by a solidly constructed soundstage, as it takes less imagination to make out the recording's acoustic and in a real sense allows you to participate more intimately in the original event. Image outlines were palpably fleshed out with a satisfying 3-D perspective. No cardboard cutouts here. This was indeed imaging at its best.
The fit and finish of the WAVAC product lineup are superlative, as their designs simply qualify as beautiful artistic creations - a blend of modern and retro styling. In the case of the MD-811 you clearly have an integrated amplifier that I can confidently recommend: an absolutely gorgeous package that not only looks and feels divine, but also sounds great.
WAVAC Audio Lab.
Effective Power output: 15 watts per channel
Final Note: (September 3, 2000): Since there have been several questions raised re the nature of the BassZilla loudspeaker kit mentioned herein, I wanted to give you a sneak review of things to come. First, the design is essentially complete. The main objective awaiting completion is the documentation, and as slow as I am about paperwork it might take another couple of months to finish.
The design represents a distillation of my ideas about deploying full-range drivers to obtain the best possible soundfield at the listening seat. The BassZilla uses a full-range driver, augmented at the bottom end by a 100-dB sensitive woofer. A Fostex FE208 Sigma full-range is used as a dipole radiator, mounted in an 18"x20" open baffle. The foundation is a 15-inch Audax PR380M2 pro sound woofer mounted in a 4 cubic foot enclosure. The open baffle is situated on top of the woofer box. I have been able to obtain very uniform and extended (40 Hz!) response at the listening seat with a sensitivity of 98 dB. The resultant soundstage is much more spacious and coherent than is possible with conventional folded horn designs.
The BassZilla kit plans are now available for sale (US$20) at the HiFi Authority.com Store
You will have to purchase drivers, etc. from vendors such as Fostex and Zalytron to construct the kits. My guesstimate at the moment for the price of the parts involved is $950/pr.