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Positive Feedback ISSUE46
as reviewed by Michael Wechsberg
If you follow tube preamplifier designs you probably know about the 6H30 tube and its use in some very fine designs by Balanced Audio Technology (BAT), Audio Research, and others. BAT claims to have "discovered" this tube when it first became available to the West after the Soviet Union fell, and I have no reason to doubt their word. They proclaimed it a "supertube" because it had electrical properties that made it close to ideal for use in preamps and line stages, compared to the 6922 or 12AX7s and such used by others of the day. The Russians developed the 6H30 for use in military communication and sensing equipment. Unlike the U.S armed forces, which quickly developed solid-state designs to replace most tubed communication gear after the production of transistors and then integrated circuits became reliable; the Russians kept their tube gear much longer and continued to improve it with new tube designs like the 6H30. It's not that Russian scientists were inferior to ours in designing solid-state circuits, in fact they were just as good if not better in some areas, but manufacturing of solid-state devices proceeded much slower than it did in the U.S. I don't have any current information, but it wouldn't surprise me if tube-based military gear is still not in use in Russia and former Soviet states today and doing quite a good job. In fact the premium 6H30 tubes that BAT uses in their most expensive preamps are devices made to the most stringent military specifications. With the VL20 line amplifier (that's what JE Audio calls it), audiophiles get the opportunity to sample the special musical qualities of the 6H30 tube at a more accessible price than previously possible.
JE Audio is a relatively young Hong Kong based audio company devoted to tube amplifier designs and the high end. Hong Kong has long been a hotbed for high-end audio and is home to some of the most avid audiophiles in the world. The annual high-end show there is the largest in Southeast Asia. JE Audio currently has two line stage amplifiers and two power amplifiers in their product line and is trying to arrange distribution in the US. The VL20 is the lower priced of their two line stages, but you couldn't tell that from the build quality—which is outstanding in all respects inside and out (see accompanying photographs above). Judging from this early product, I predict JE Audio will have a long and prosperous run.
The VL20 has many features similar to other preamps and line stages that use the 6H30. It is a wideband (over 500kHz bandwidth), balanced design with just a single gain stage (about 14dB of gain), no global feedback, and no load resistors or buffers. These attributes are meant to minimize phase shift in the audio band to preserve soundstaging and imaging. The balanced design also minimizes electromagnetic interference picked up internally or externally (say through one's interconnects). The VL20 has both balanced and unbalanced inputs and outputs, but JE Audio asked PFO to supply a reviewer who could evaluate the line stage in its balanced configuration for best performance, so yours truly got the assignment. The VL20 uses four Sovtek 6H30 tubes for amplification, one each for the positive and negative halves of the balanced signal. JE Audio hand selects each tube and matches them for use in the preamplifier. The 6H30 is like a small power tube giving the VL20 an astonishing 40V output capability into 100kohms, yet it's super quiet. The tubes are broken in for 50 hours before being measured for use in the preamplifier. JE Audio advises the line stage requires an additional 50 to 100 hours of burn-in before coming up to its best performance. JE Audio told me they burned my unit in at the factory for about 50 hours and I let it play another 48 hours or so over a couple of weeks before I began listening tests. I found that about 30 minutes of warm-up before each listening session was worthwhile. Although the unit uses only about 70W I did not want to leave it turned on all the time lest tube life be degraded. Interior views reveal a hefty regulated power supply and good quality components and workmanship throughout. The circuit is very simple and the parts count is low—usually a good sign for better sound quality.
The mechanical design and external appearance of the VL20 are also very impressive. The all-aluminum chassis is quite large for a line stage and weighs an impressive 33 lbs. The front panel sports two aluminum knobs, one for input selection (4 are provided, both balanced and unbalanced for each) and the second for volume. The most notable feature of the front panel is the engraved wording "Balanced Tube Amplifier" that might lead you to believe this is a power amplifier instead of a line stage. The rear panel has all the doubled inputs and two outputs, one balanced and a second unbalanced. No power cord was supplied with my unit so I used an XLO Signature 3 cord I had on hand (see review in issue 45). There is also no remote available—good for the purists but poor for us lazy reviewers. Three hefty feet with compliant bumps on the bottom support the chassis and provide vibration isolation and mechanical stability.
The four 6H30 tubes are located in a chimney structure, open from top to bottom, in the center of chassis. A metal grid protects the tubes. I'm sure this configuration is used to provide good ventilation, but it was nice to get a glimpse of the glowing tubes each time I got up to adjust the volume. The big bold lettering on the front panel and the tube chimney give the linestage a distinctive and expensive look. Except for the lack of a remote, the VL20 has all the features, plus the look of a device considerably more expensive than it is.
I wired the VL20 into my new E.A.R. reference system, substituting it for the E.A.R. 868 preamp. I used Harmonic Technology Magic™ Link Two balanced interconnects between the linestage and E.A.R. 890 amplifier, and XLO Signature 3 balanced interconnect between the E.A.R. Acute CD player and the VL20. Speakers were the Marten Miles 2.
One CD I used extensively in my listening tests of the VL20 is the Hugh Masekela recording called Hope. This is actually an SACD, but I used the CD layer for my tests (little or no degradation in sound when using the Acute CD player). Hope is a vibrant live recording that I have heard over some outstanding systems including my own. The VL20 at only $2500USD gets about 85 to 90 percent of the best this recording has to offer. The lows are especially deep and fast and voices are lively and realistic. The sound space is rendered well and when the audience is heard it sounds like the real thing. Compared to the best I've heard, some of the shimmer and air around the horn instruments is missing and the coherency that gives the recording its drive and "boogie" factor is a bit lacking. But overall the VL20 does an outstanding job on this recording.
Other recordings I tried of male vocalists and small jazz ensembles brought out the smooth and generous midrange response of the VL20. I'm sure this is the sound that makes using the 6H30 such a winning proposition. When I rolled out my group of female vocal recordings I was sometimes bothered by a definite forwardness in the upper midrange. The VL20's overall sonic signature is one of being warmer rather than drier, but the balance seems to be tipped up a bit in the mid to upper midrange. While I didn't notice it much on male vocals it was there in almost all the female vocals I played. Not unpleasant, but just not to my taste. Perhaps a different power amp or set of interconnects would match better with the VL20 in this respect. I noticed the same frequency balance on several classical recordings; especially pieces with prominent string parts. Again the nice warm sound was very pleasing, but not quite what I prefer. You will have to listen with your other components to decide whether this is to your taste.
On the other hand, the VL20 is a soundstaging champ when used in the balanced configuration. Instruments are solidly located in space and the soundstage is broad and deep. I would expect this from the stated design philosophy with its attention to minimizing phase shift. The VL20 has a very musical high end, but it's just a little short in transparency and definition compared to some of the better line stages I've heard. Although the VL20 plays loud and has outstanding macrodynamics that make music very exciting, the microdynamics that enhance the sense of realism were not as good.
I didn't have any other balanced interconnects on hand to experiment with in potentially tailoring the VL20's sound, but I did have a variety of single-ended interconnects. First I tried the single-ended XLO Signature 3 interconnect between the Acute and the VL20. This is in the same family as the balanced interconnect I had been using, so I expected a similar sonic signature and that is exactly what I heard. Sampling several recordings, I did not find a significant tonal shift, but I did notice a narrowing of the soundstage and slightly poorer image specificity. The recordings lost some of the jump factor they had when balanced cables were used, but the music that kept spilling out that was very pleasing and convincing.
Next I tried some DH Labs Silver Sonic interconnects. From previous experience these have a sonic signature that favors the high end and is quite different than that of the XLO cables; and so it was with these cables in the system. Highs were a little more delicate on some recordings and a bit hotter on others. Lows on the other hand were less distinct and the overall soundstage was flatter and images were less precise. The warmth on female vocals and strings was still about the same, maybe even emphasized a little more. My conclusion from these brief experiments changing interconnects is that the VL20 itself is a pretty transparent device and one that requires careful system matching.
The VL20 is really a very good line stage and a screaming bargain at its price. Remember I'm comparing it to the E.A.R. 868 that costs three times as much. This may be the most affordable way to enjoy the special qualities of the 6H30 tube sound. The build quality is terrific with the only flaw being a lack of a remote. The circuit is simple doing the minimum damage to the signal passing through it. However, it does have a sonic signature that may or may not be to your liking, depending on what kind of music you normally listen to, so one should choose interconnects and other equipment carefully to achieve the best possible sound. Use the VL20 in an all-balanced system for best results but don't be afraid to use it in you single-ended system as well. I look forward to more and even better things from this young company in the future. Michael Wechsberg
VL20 Line Amplifier
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