The Yoshino V20 Integrated Amplifier
By Dick Olsher
Note: This review was originally slated for publication in Fi Magazine. And if it weren't for petty politics, it would have seen the light of day well before Fi 's demise. In fact, it amazes me that a significant product of the V20's caliber has yet to receive a full review in the US press; a black mark on the collective record of a paper press focused it seems much of the time on trivial pursuit or satisfying big advertisers. So here it is, dear Audio Mecca faithful, a first look at the V20 integrated amplifier.
I have to admit that I chuckled when I first got wind of the V20. The idea of using the venerable 12AX7 (ECC83) dual triode as a power amp output tube sounded more than just a bit bizarre. After all, the 12AX7 is a small signal or preamp tube intended for voltage amplification. After its release by RCA in 1948, it became one of the most popular receiving tubes of all time. It's high Mu (i.e., gain capability) and low cost have made it a no-brainer choice for the front end of countless amps and preamps. Each plate has a design maximum rating of only 1.2 watts (or 2.4 watts when both sections are wired in parallel). Pretty puny relative, for example, to the 35-watt rating of a 6550 beam power tube. On the order of 15 paralleled 12AX7s would equal the plate dissipation of a single 6550. So why all the effort to push the 12AX7 into service as a power tube?
When I caught up with designer Tim de Paravicini at the 1998 Consumer Electronic Show, during a rather noisy Fi Magazine party, I put exactly that question to him. As I recall, Tim shrugged and said something to the effect that it had never been done before and that it was considered an impossible task. OK, Tim, I realize that sending a miniature triode -- in essence a boy -- to do a man's job is a formidable task, but I was sort of expecting a more complex answer. For some men a challenge is a mountain that must be scaled -- simply because it exists. I respect that, but I was hoping the rationale had a lot to do with exposing the secret life of the 12AX7 -- unlocking, if you will, a secret sonic treasure. I mean, if the payoff can't be measured in terms of sound quality, then the means clearly don't justify the end. Well, as you'll see shortly, de Paravicini has in fact opened a door into a new dimension of tube sound and I'm certainly glad he chose to take the road less traveled.
The name -- V20 -- represents an allusion to the V12 Jaguar engine and reflects Tim's passion for automobiles. It is also exactly the number of valves (British for tubes) used in the output stage of both channels. There are 10 12AX7s per channel, with 5 tubes paralleled in each phase of the push-pull circuit. So all in all, there are 10 triode sections per phase. This, however, is no ordinary push-pull circuit. Tim's innovative touches are all over the place. For starters, the output stage is operated in "Enhanced Triode Mode," which means that each output tube has its grid biased positive with respect to the cathode. This obviously results in grid current, but allows the 12AX7 to handle much more power in a linear and reliable manner. Another de Paravicini invention is the "Balanced Bridge Connection," originally used in the E.A.R 509 power amp. The primary windings of the output transformer are equally split between the anode and cathode circuits to increase linearity and bandwidth, in a manner similar to the McIntosh unity-coupled circuit of 1949. The two primary windings are capacitively coupled to ensure push-pull symmetry at high signal levels. This arrangement results in an output stage of unity gain and large current draw and requires a robust driver stage. The front end consists of three differential (i.e., balanced) voltage gain stages followed by a cathode follower driver stage. Low levels of feedback are taken from the primary side of the output transformer to the first two gain stages. The power supply is all solid-state.
The total tube complement is 30 tubes: 26 12AX7s and 4 12AU7s. That folks, is a swarm of tubes! However, the retubing costs should be very reasonable. The US importer and distributor, Dan Meinwald of E.A.R USA, tells me that a factory retube kit for the V20 only costs $300. Believe me, that's a lot less that what you'd pay for a high-quality octet of 6550s or KT-88s. And please don't go off the deep end tube rolling expensive and exotic New Old Stock 12AX7 brands such as Siemens or Telefunken into the V20. Based on some limited experimentation, I can tell you that the stock tube complement works extremely well, so don't fool with it. Instead, save your money and support the music industry: buy some new albums.
Let's all put our hands together and applaud the appearance of another integrated amplifier (IA) on the American market. The concept makes a lot of sense and is quite common place in the UK and Japan, but has been slow to catch on in the US. Part of the problem is the audiophile dogma that preaches that separates are generally better, that the combination of a full-function preamp and basic power amp offers greater sonic potential than an IA, and that an IA is merely a cost savings compromise. Well, you can take that dogma out for a walk and lose it. The truth of the matter is that in this day and age of CD player dominated systems, an IA is your best bet for optimum sound. It makes no sense to me to invest a lot of money in a separate preamp, when the CD player output is in the range of 1 to 2 volts. I routinely run my Accuphase CD players directly into the power amp by using the Accuphase's digital volume control to set playback levels. Take my word for it: simpler is better. Less cable and at least one less gain stage translate into cleaner, more immediate sound. There's no line-level preamp that sounds as good as the direct bypass.
The V20 is actually nothing more than a basic power amp with a function selector switch and volume pot at its front end. A total of 5 line-level inputs are provided for sources such as CD player, tuner, and tape deck. With an input sensitivity of 400 mV, just about all line sources out there should be able to drive the V20 to full power output. An attenuated line-level output for a tape recorder is also provided. If you're still into vinyl (as I am), a phono stage may be connected to one of the line inputs. Note that this is a purist design to the extent that there is no balance control, mono switch, or filters.
Imagine participating in a blind wine tasting session. Glass after glass of familiar bouquet passes you by, until suddenly your palate encounters something completely different. A flavor so deliciously distinct from anything you've encountered before that it defies recognition. That in a nutshell was my experience with the 12AX7 based output stage of the V20. It is difficult to definitively assign a particular personality to a given tube type because ultimate performance depends in part on the amp's operating point and the quality of the power supply and output transformer. But if I may be permitted to generalize, let me give you a few examples of my own findings over the years. It's safe to say that the harmonic flavor of the EL34 is on the gutsy and bluesy side of reality, but lacking the ultimate in finesse. And that's pretty much the story behind most power pentodes. In contrast, he EL84 (6BQ5) beam power tube has been used frequently to produce 20 to 30 watts of sweet tube sound. Although its sound can be fairly characterized as sweet, the EL84 lacks lower midrange body and punch. Honeyed, but with exceptional lower midrange projection, the GEC KT66 delivers vintage tube sound. Hailed (by the manufacturer) as the finest audio tube ever made, the KT66 was the king of the hill in the 50s in the UK, finding its way into such amps as the Leak and QUAD. In its original form, the KT66 was plagiarized from the RCA 6L6, and in 1957 GEC continued its copycat ways by unveiling the KT88 which was pretty much equivalent to the 6550 first marketed by Tung-Sol in 1954. Some would argue, and I tend to agree, that the original British KT88 sounded more vivid and better focused than its American equivalent. The 6550 and KT88 can best be described as big, authoritative, and quite magical (i.e., bigger than life) through the upper midrange.
OK, so where exactly does the V20 with all of its 12AX7s fit into this spectrum of tube sound? On the basis of size alone, one might expect the V20 to most closely approximate the sound of an EL84 based amp. To some extent, that's not a bad starting point. The V20's rendition of harmonic colors was suave and smooth, with a believable sugar coating. Violin overtones shone brilliantly and sweetly. The upper registers of soprano voice were reproduced with convincing sheen and tonality. The upper midrange was lucid to an extent that exceeds the performance of any tetrode or pentode in this area. The V20 blows away EL34 based amps in these respects and should, more appropriately, be compared to push-pull power triode based amps. In fact, its level of clarity and textural smoothness was reminiscent of that of the Western Electric 300B. But consider the price differential: about 300 common 12AX7s may be purchased for price of a single new Western Electric 300B.
No, the V20 is no bad ass EL34 kind of amp, but because I held residual doubts or preconceived stereotypes about the punch factor of a 12AX7, I was in for quite a surprise. For the record, I did expect a "Snow White" amplifier: pretty, pure and virginal. What actually jumped out of the box was in essence Madonna. That is to say, the lower mids had a substantial amount of "sex appeal." The power range of the orchestra was full bodied, warm, and dynamic. In this area, the miniature 12AX7 came close to equaling the magic of the KT66 and KT88. But note that the V20 is not a romantic sounding amp. It fails to deliver the excessive warmth or lushness that characterizes so many vintage tube amps, and it certainly lacks the warmth of E.A.R's own classic, the model 509.
Treble transients were reproduced with speed, finesse and a flair for the natural -- without the glare that afflicts pentode-based amps and is often mistaken by the neophyte for true detail. There was plenty of detail to behold. In fact, the V20 earns my "X" rating for its exposure of low-level detail, even in complex passages, without leaving anything to the imagination. But, and that is the crucial difference, it all flowed naturally within the fabric of the music. The extreme treble was open and airy sounding. The bass octaves were well-defined and capable of decent dynamics when mated with a suitable speaker. The V20 provided plenty of bass punch and definition when mated with the Samadhi Acoustics Ichiban loudspeaker off the 8-ohm taps. What I'm describing is a moderately efficient speaker (86 dB) with an easy-to-drive impedance magnitude situated in a 14 by 24-foot room. If your speakers are at least that sensitive and your listening environment falls within these constraints, expect the V20 to deliver adequate playback levels. The V20 clipped only rarely under these circumstances, usually on a whopper of a bass transient, but recovered quickly and gracefully.
The soundstage was fully fleshed out with excellent image specificity and a wonderful transparency. Stage width was literally from side wall to side wall. Stage depth was dependent on the position of the speaker in the room. About a third of the way in form the rear wall, the depth perspective became absolutely cavernous. The real magic of the V20, however, was its coupling of speed, resolution, and precision with intimacy. I was continually drawn into the emotional content of the music. Stepping into the Gestalt generated by the V20 became for me an addictive experience, as it may for you. I suggest that the following warning be appended to the Owner's Manual: Caution -- listening to this amp may be habit forming!
Neither soft sounding nor overly lush in the mold of vintage tube gear, the V20 represents a unique amalgam of old and new tube sound. Above all else, I found its musical virtues to be most persuasive: smooth, dimensional, and harmonically rich, with enough sex appeal to make me want to come back for more. This is a gem of an integrated amp and easily the best sounding integrated I've heard to date. For example, it is clearly superior in terms of resolution to both the Mesa Tigris and the Luxman SQ38S that I recently reviewed for Fi. This amp isn't into horsepower and as such may be under powered for most audiophiles' egos. If you buy one, buy it for the right reason, from the perspective of a music lover whose main interest is in rekindling the emotional content of the music. Highly recommended.
Rectory Farm, Cambridge Road
Cambs. PE18 8BP
1624 Sunset Ave.
Santa Monica, CA 90405
Warranty: 3 years limited (90 days on tubes)
Dimensions: 420mm (W) x 135mm (H) x 440mm (D)
Weight: 22 kg (48.4 pounds)
Number of Years In Business: 20
Number of Dealers: 27
Tube Complement: 26 ea. 12AX7 (ECC83); 4 ea. 12AU7 (ECC82)
Power Output: 24 watts per channel (20 Hz - 20 kHz)
Power Bandwidth: 12 Hz - 80 kHz at -3 dB
Inter Modulation Distortion: < 0.5%
Output Damping Factor: 10
Signal to Noise Ratio: 93 dB
Input Impedance: 47 kOhm
Loudspeakers: Samadhi Acoustics Ltd. Ichiban and Magic Cube
Digital Front End: Accuphase DP-75 CD player
Analog Front End: Oracle Delphi Mk. V turntable w/Graham 2.0 arm and Grado Reference cartridge
Phono preamp: Air Tight ATE-2
Speaker Cable: Acrotec 8N; Fadel Art Products Streamflex Plus.
Interconnects: Acrotec 6N and 8N; Fadel Art Products ICS-15S.
Accessories: Ultra Resolution Technologies Bedrock equipment stand; VansEvers Clean Line 85 and the Unlimiter; Townshend Seismic Sink.