November 2002

WAVAC MD-300B Single-Ended Triode Amplifier
Review by Wayne Donnelly
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  The MD series is WAVAC's "economy" line of SET amplifiers. That may surprise the reader who is unfamiliar with WAVAC products, because the MD-300B looks pretty ritzy with its gold-tone chassis and dark wood fascia, ceramic tube sockets and heavy glass tube screen. An examination of the top-of-the-line EC-300B ($20 K) restores perspective -- three times the money gets you a chassis milled from a solid block of aluminum alloy; tube sockets milled from Teflon, and an extraordinary level of parts quality throughout, including stratospherically costly transformers that enable the EC-300B to attain a bandwidth of 20Hz to 100kHz. But by any reasonable standard, the MD-300B is itself quite a deluxe package.

Design Overview

WAVAC SET amplifiers are all based on a circuit developed by Japanese designer Nobu Shishido. This patented circuit features Inverted Interstage Transformer Coupling (I ITC) to deliver an optimized signal to the output tubes. There are no coupling capacitors in the MD-300B, and its direct-coupled signal path contributes significantly to the amplifier's tonal purity. In addition, the physical construction employs vibration control techniques.

Transformer quality is especially critical in SET amplifiers, and WAVAC winds all of its transformers in-house. A filtered DC source supplies the 300B heaters, minimizing hum and noise. The amplifier also has a power line input filter to reduce noise from incoming AC power. 

SET amplifiers typically require a lot of attention. Some need re-biasing virtually every time they're powered up. But the MD-300B is self-biasing. If you switch from one 300B to another, you need not worry about the bias. That is, as long as you are using 300B tubes that conform to the electrical parameters represented by the Western Electric 300B; there are "300B" tubes from KR, Vaic, and possibly other manufacturers which differ significantly from those standards and should not be substituted in this amplifier.

External Tour

The neatly organized rear panel holds the IEC socket, three pairs of RCA input jacks and one pair of loudspeaker terminals. The latter, chosen, I'm told, for sonic excellence, should be handled carefully. These inch-long cylindrical terminals are attached to the chassis with nuts which can loosen easily. At one point, while changing loudspeaker cables, I inadvertently unscrewed a terminal, which required opening the bottom of the amplifier and some crafty work with needle-nose pliers to reattach.

The front panel holds the customary large WAVAC Power button and two attractively sculpted knobs for input selection and the passive volume attenuator. Note: the MD-300B is not an integrated amplifier; there is no pre-amplifier gain stage. The passive control does offer interesting possibilities, about which I will say more later.

Review Environment

The MD-300B dropped nicely into my primary system: Basis 2800/Graham 2.2/van den Hul Black Beauty for LPs; hot-rodded Pioneer 434 DVD/CD player; and Thor TA-1000 line and TA-3000 phono pre-amplifiers. Arriving around the same time as the amplifier were the Von Schweikert dB-99 loudspeakers, smaller siblings to the dB-100s that recently won a Best of 2002 award on Enjoy the Music.com™. The dB-99 (the number refers to its sensitivity) is a very good match for the 10 wpc output of the MD-300B, especially since their bass systems incorporate a 400-watt amplifier in each enclosure. 

For a few days I used the amplifier to drive the Meadowlark Swift loudspeakers reviewed in October, with very good results. But the listening experiences described below refer only to the dB-99. An assortment of interconnects, loudspeaker cables and power cords from Transparent, Nordost, TG Audio and Bybee, as well as numerous accessories (including the Townsend 3D Seismic Sink reviewed in this issue) saw service during the review.

Choosing the Coolest Tubes

At its basic pr ice of $6,100, the MD-300B typically comes from WAVAC with Valve Art or EH 300B output tubes and new production ECC81/12AT7 input tubes. But Jim Ricketts of tmh audio, who distributes WAVAC in North America, is a confirmed tube roller who is always looking for ways to get even better sound from the WAVAC amplifiers. For the MD-300B he offers at a price of $6800 a choice of Western Electric or TJ silver mesh plate, ceramic base, gold pin 300B output tubes and premium NOS input tubes -- currently Mullard CV4024. I received the review amplifier with the TJ and Mullard tube complement.

When auditioning the EC-300B amplifier a few months ago, I had a small shootout between the WE and TJ meshie 300Bs. In that amplifier I ultimately preferred the TJs, finding them livelier and more open-sounding compared to the darker sound of the WE. (A point worth repeating here is that one should not assume that tube comparisons like this will hold true outside the amplifier in which they are compared. Differences in circuit design and parts may lead to very different results.)

Over the last couple of years I have become increasingly interested in -- and impressed by -- the benefits of cryogenic treatment on audio hardware (and software). That subject is worth a long article to itself, but that's for another time. I mention it here because when the MD-300B arrived with the TJ 300B tubes installed, I just happened to have on hand a pair of WE 300Bs that had recently been cryo-treated. After a few days I substituted the WE's, and found that I now preferred them to the non-cryo'd TJs. After a couple more days of listening -- and with permission from Jim Ricketts -- I took the TJs and the various input tubes Jim had sent for me to try over to the local cryo boutique.

After I reinstalled the cryo'd Mullard input tubes, the character of the MD-300B's already excellent sound was subtly enhanced. Instantly notable was a greater sense of spaciousness and air that drew me even deeper into the music, especially with orchestral recordings. Although it took a little while to pin down, I also realized that there was a more relaxed and natural quality in the sound of the system.

Next was a repeat of the 300B shootout with both brands cryo'd. And now the TJs had regained the edge -- not huge, but definite - over the excellent WE's. The TJs made the MD-300B sound faster and more dynamic, as well as further opening up the high frequencies. Bass definition was pretty much a wash between the two tubes. The Mullard/TJ combination remained in place throughout the review process, which I began with the MD-300B as a straight power amplifier driven by the Thor TA-1000 pre-amplifier.

Listening to the MD-300B

I must confess that somewhere in the back of my mind was lurking an irrational hope that the MD-300B would turn out to be the sonic identical twin to the magnificent EC-300B, which remains the best SET amplifier I have ever encountered. Since this is the real world, that hope was not fulfilled. There is a lot more than cosmetics separating the EC-300B from its little brother. 

The most immediately obvious difference is in deep bass. Although the combination of the MD-300B driving the active transmission-line bass system of the dB-99s produced very potent low frequencies, memory kept insisting that the EC-300B had been even better. The difference is most notable with recordings prominently featuring huge bass drum strikes -- the Bernstein CD on Reference Recordings, the new Telarc 1812 Overture, and an old favorite, the scherzo of the Mahler Resurrection Symphony on an EMI LP with Otto Klemperer conducting the Philharmonia Orchestra. I also detected slightly less weight with massed low strings and synthesizer passages. On most program material, however, there was no sense that bass was lacking, and not one of the many visitors who came by to hear the MD-300B had any negative comment. You'd need loudspeakers capable of significant controlled output below 40 Hz before the question would even arise.

To continue this unfair comparison, the top end of the MD-300B is slightly less extended than that of its costly relative. Taken on its own, however, the highs coming from the MD-300B are superb -- open, spacious, with lots of air, especially with the TJ output tubes. With recordings as diverse as the Classic 45 RPM LP reissue of the Reiner/Chicago Pines of Rome (first movement especially) and Alison Krauss and Union Station's New Favorite CD, there was really nothing in the high-frequency range to criticize.

As with virtually all SET amplifiers, the most glorious aspect of the MD-300B's sound is the midrange. The comparison? OK, the EC was the closest to absolute tonal neutrality that I have heard from any SET amplifier. Comparatively, the MD-300B has just the slightest touch of warmth -- and that's not a bad thing. It's very hard for me to criticize a component or system for sounding too beautiful, and voices, string instruments, piano -- heck, virtually everything -- sound gorgeous through the MD-300B.

I hope it's clear that I have been making comparisons between the $6800 MD-300B and the $20,000 EC-300B (the state of the 300B SET art, in my experience) not to criticize the little guy, but to emphasize how close it comes at one-third the price. I have had to only a few components in my system with what I'll call " walk-into-the-room appeal." Several times during the review process, visiting music lovers commented immediately about how good the system sounded, without knowing what amplifier was in use.

Going Solo

It's easy to understand the appeal of matching passive attenuators with power amplifiers. Removing the pre-amplifier from the chain eliminates at least a couple of gain stages as well as a set of interconnects and two sets of jacks -- all of which can potentially add colorations and distortion. But in listening to passive volume controls over the years, I have more often than not found their benefits offset by losses in liveliness, color, bass and overall dynamics -- and in most cases I have ultimately preferred the active pre-amplifier over the passive attenuator.

Since the MD-300B is equipped with the passive control and three sets of inputs, I wanted to evaluate it with the Thor line stage removed, playing the Thor phono stage and a couple of CD players directly into the amplifier. I soon discovered the need to be careful in switching between inputs. The first time I did so, with the volume up at a healthy listening level, the system emitted a frightening switching transient -- the kind that can damage a speaker driver if it is loud enough. 

Probably with an eye to keeping the circuit as pure and simple as possible, WAVAC does not buffer the input selector switch. Believe me, it takes just two or three of those nasty pops to teach you to turn down the volume before switching inputs. Problem solved.

The sound of the MD-300B with and without a pre-amplifier turns out to be more alike than different. There is a slight diminishment of dynamics, but it is noticeable only with amplifier-challenging musical material. I also noted that it was possible to max out the volume control with some LPs -- no surprise since the gain of the line stage had been removed. The maximum level was high enough to satisfy 90 percent of my listening needs. And ultimately I find that the midrange seems slightly purer and the highs livelier with the passive control. I have no hesitation in recommending that any prospective buyer of the MD-300B give it a good audition sans line pre-amplification, if its three inputs are sufficient.

Summing Up

This one is easy. The MD-300B looks and sounds great. It is very well built and finished with great attention to detail. I have not heard the "factory stock" configuration, but I feel pretty confident that the upgrade offered by tmh audio is worth the additional $700. The sonic chemistry of the MD-300B and the highly sensitive, extremely dynamic Von Schweikert dB-99 or dB-100 promises a listening experience that I suspect few SET aficionados have had. If you are looking for a great 300B amplifier, you owe it to yourself to check out the WAVAC MD-300B.

Specifications

Frequency Response: 40Hz to 50kHz

Power Output: 10 wats per channel

Input Sensitivity: 1.0V rms

Input Impedance: 100Kohms

Signal to Noise: 80dB

Dimensions: 265 x 420 x 200 (WxDxH in mm)

Weight: 17 kg.

Warranty: one year parts/labor; six months on tubes

Price: $6,100 standard, $6,800 as reviewed

Company Information

WAVAC Audio Lab - Sigma Co. Ltd.
1404-26 Nakada-Machi Yonezawa-Shi
Yamagata, Japan

Website: www.WAVAC-audio.gr.jp

North America Distributor

tmh audio
P.O. Box 751681
Dayton, OH 45475

Voice/Fax: (937) 439-2667 
E-mail: info@tmhaudio.com
Website: www.tmhaudio.com