Review: Yamamoto CA-04 Preamp 6AK5 403A Tube Rolling 45 Micromega Stage 2

Click pics to enlarge. Micromega Stage 2 CDP to the left of the Yamamoto CA-04.

Review: Yamamoto CA-04 Line Preamp, A-08S Amp
Talk Tube: 45, 6AK5
My Japanese Fetish

Amended Aug 13. 2020 (twice): Triode vs Pentode paragraph added. Also more comparisons. And re-write of the Japanese Preamp section.

The good old days! In Central, Hong Kong, there was a well known second-hand store, Reference Audio (now in Mong Kok). Over the years, I bought many things from them, including the EAR 912, but what I bought most were Sun Audio kits. They used to carry the entire Sun Audio line, at special prices, half that of US or Japan. Hence I built their 2A3, 300B, VT-25 and yet another 300B amp using the VT-25 kit's 5K tap. All this was before I started this blog (in 2008) so I never wrote about them here. It's about time I do an Overview of Sun Audio, sadly under-represented in the US.

pic of A-08S from TNT.
 

Yamamoto A-08S
It was at Reference Audio that I first saw the Yamamoto products. One look, and I knew I wanted them! But they were kind of pricey for me (I was more of a cheapskate then). I can't be sure when, but it was before 2008 (when I started this blog; I'd have written about the A-08S otherwise), when I was back in the US, that I ordered a kit A-08S through the US dealer Brian Bowdle (now defunct Venus Hi-Fi, very nice guy). I also bought my Almarro A-318B and MA-1 through him. I chose to have them in NYC because I had too many SET amps back in HK (and most of the Japanese SET amps do not have multiple taps for voltage conversion).

For a detailed introduction to Yamamoto Products, including the original A-08, read this early Jeff Day 6moons article. The article features several home visits, including at Cain and Cain (of Abby fame). There is also an Art Dudley review of the A-08. The A-08S adds a sexy meter, as well as some change in DC coupling to lower the noise level even further. Read the TNT A-08S review.

The A-08S is lovingly nicknamed "The Sushi Table". It took a while to build the kit. Parts are of high quality, and a pair of NOS Western Electric 717A and 45's, as well as an 80 was included (amazing!). If you are interested in the building process, my friend daiwok chronicled it here, with many pics. Incidentally, the use of the "mini doorknob" pentode WE 717A is one reason why I chose this amp. Any WE can only be a plus. More useful info and great pics can be found on this page of jacmusic.

Sound I shall not elaborate on the sound. It is as described in those reviews. To summarize, very quiet, clean and neutral, yet with no etching. Surprising power for 2 wpc, a fast and tactile bass, and of course, great presence (the sine qua non of SET). It will fit a rich sounding system with good bass foundation more than a bright system (usually light in bass). It is entirely possible that some SET aficionados will not like this kind of sound. Often I read that SET amps are sweet, rich, chocolaty...that puzzles me to no end and I attribute that to wrong design and component choice. Most of my SE amps are not like that, just varying but small degrees on the tube side of neutral. The A-08S is certainly not rich sounding. Is this the Yamamoto sound? Partly, but I'd not attribute the sonic character entirely to Yamamoto...

45 The immortal Triode 45 itself has a very clean sound (even more than the Beam 6V6) akin to the single-plate 2A3 (vintage as well as current), which sounds cleaner (leaner) than the vintage double-plate 2A3. I know the sound of 45 well, as I have another DIY one in HK. That one has a WE 417A as driver and Tango Output trannies, and sounds a little sweeter than Yamamoto (the 417A is a great tube). Nonetheless, the character of 45 is very much in evidence. The 45 is one of the best triode tubes. Brands are not important. There are hundreds, if not thousands of types, so getting a "matched pair" would be difficult. I'd not bother, take any two and they will sound great in a SET amp. The 45 goes back a long way, to the WE era. ALL of the currently produced Triode tubes, be it 300B, 2A3, so-called PX25 etc, will pale in comparison. Of course, for 2 wpc, you need efficient loudspeakers. 45 is also cheap, much cheaper than some of the boutique, high-priced but under-performing tubes now. Globe 45's are more expensive, and usually they sound warmer, but one may just prefer the ST shouldered ones, which are bargains. As I have heard 2A3 PP to great effect (Brook 10/12, and I have also heard a pretty good DIY effort using vintage trannies) one day I hope to hear a 45 PP amp (I have seen the vintage RCA monoblocks but never heard them)!

My Japanese Fetish is largely confined to SET amps I have a long relationship with Japanese Single Ended Amps. After all, they were among the first to revive SET. American SET makers come much later (and we can forget about the few European efforts, except Verdier). Having heard some Wavelength, Welborne and Bottlehead, I must come to the conclusion that they don't reach the standards of the better Japanese products. A crucial factor is in the transformers - it is my belief that the Japanese make better SE Trannies. Of course, topology and component choice all contribute to the sound. Let's just say the Japanese amps have a little more of that je ne sais quoi. I know, some would think of it as an "ephemeral" thing but, having been in this hobby for so long, that's an important aspect of the audio lore (think WE). PP Amps But when it comes to PP I am not interested at all in current Japanese (or American or European) products, at any price level. I own a Shindo preamp, but I am not interested in a PP Shindo amp. Why? Because vintage PP trannies are better! There is no way any current PP amps can sound better than vintage amps in good condition. Hence, imagine my puzzle (and my friend Hoi too) when I heard the uninspiring Sun Audio 2A3 PP monoblocks (not even close to the Brook 12A that I have) which is essentially the same as the 300B PP Gizmo raved about (here). Preamps Readers may think I am really interested in Japanese Preamps, as they don't have to use output trannies. Well, not really. I just have too many good Preamps already. But I have made several exceptions: I decided to buy the Wavac PR-X2 after I bought the wonderful Wavac MD-300B (here) and Kondo M7 sometime after I got the Ongaku (so a desire to hear a full system after I got the amp); Leben RS-28CX (here) independently, since I am not interested in their PP amps; and now, the featured Yamamoto CA-04, also because I already heard the A-08S amp. And of course, given my kit building bent, the overachieving (and now legendary) Elekit TU-875 and the current TU-8500. Well, that's quite a few I guess, more than I'd have thought...

Yamamoto CA-04 Line Preamp
The Preamp did not receive nearly as much attention as the A-08(S) amp. The only review is in Positive Feedback. Although  I saw almost the full line in HK, I didn't think much about them. That changed after I got the A-08S. Recently, I chanced upon one in NYC, and bought it. The nice seller delivered it to me, no shipping!

Confession. My interest in this preamp is also in part due to its unusual use of a pentode, the 6AK5, which has a Western Electric Equivalent, the 403A. This is a good sounding (and small) tube. The Chinese equivalent 6J1 is widely used in cheap preamp/headphone amps. Since I have the FX Audio TUBE-01 (here) I already have some old-stock 6AK5s around for rolling. And old stock tubes (6AK5/EF95/5654/403A) are not expensive.

Some more data and great pics of the innards can be found on this page of jacmusic.

Contruction, Parts Quality and Circuit I love its size and proportion. It is a lovely looking unit. Inside the wood trim is a solid steel chassis. Unusually (for Japanese high end) it uses a U-shaped circuit board. The 2 sides are broad. In my line stage version, basically only 1 side is used for the PS (the other and largely empty side is for the phono option). A slender strip bridges the 2 sides and this houses the 2 proprietary Teflon tube sockets for the 6AK5. Inside the trough are anchored the selector and double-ganged volume pot, which are very ordinary looking things, frowned upon by many DIY people. This is not cost-cutting. Almost down to the last one, Japanese designers feel simple selectors with small contact points and carbon pots, despite their tracking anomalies and other perceived faults, are more musical. I must say, based on my past, hanging out with DIYers, auditioning of a huge number of expensive but sterile sounding components, I concur. Funny, I posted a pic of this preamp on my Chinese wechat audiophile group, and the first comment I got from a DIY friend was: "change the volume pot!"  😃. Now, the PS is on the circuit board, and the only thing I have reservation about is the power transformer is soldered onto the board. Given my Dynaco PAS3 experience I'd have preferred an isolated PS. Here I cannot provide more isolation. The power transformer is actually very nice and looks to be a quality double C-Core. Here it is interesting again. Different from many other Japanese manufacturers, this has both 120 and 220V winding's, as the seller was using it in HK and took it back to the US and had a technician convert it. Rectification is SS. It should be mentioned that the circuit is quite simple. The signal travels a short path via the circuit board (only around the few components associated with the tube amplification). Otherwise, the preamp is largely hard-wired (inputs to selector to volume pot to studs on the circuit board (on the slender bridge). The output cap (and one in the PS section) is encased in wood. It is certain the designer tuned the gear to his satisfaction.

The unit came with Telefunken 6AK5s, which are the original tubes supplied (as with the A-08S, Yamamoto is classy, always good tubes). I hooked it up to my streaming system:

Bluetooth: Dayton BTR-01 digital out (Belden 1694A)
DAC: Micromega MyDAC (Kimber KCAG)
CDP: Micromega Stage 2 (Gotham DRG-1)
Turntable: Technics SL-1200 Mk II/Denon DL-103
Phonoamp: Schiit Mani (old Audio Note AN-V)
Preamp: Yamamoto CA-04 (Gotham GAC-2111)
Amp: Akitika GT-102 (Gotham 50025)
Speakers: Almarro MA-1

Initially, I was pleased by the refined sound, but soon some dark clouds rolled in. I was missing some microdynamics. Also, the spec says 16 db gain, but it sure didn't sound like that as my volume knob was way up. I was puzzled. With this kind of gain, the -20db setting for each input would be unusable!

I decided to tube roll a little. I swapped in a pair of Sylvania old-stock tubes. Holy cow, all the gain is back, and microdynamics galore! So, the stock tubes were on their last legs! But the Tele's still seemed to have a little more detail. So I went onto Ebay and got some used (but test strong) Telefunken's and WE 403As as well as some others.

Sound Most of the words used to describe the A-08S can be used to describe the CA-04, though I think the CA-04 is perhaps just a little sweeter in nature. It throws a cavernous and airy soundstage. It is very quiet, clean and neutral. This is a "lighter", refined, yet lithe and nimble kind of sound, with a pacey but fluid delivery. I actually take issue with what the Positive Feedback reviewer said about the "lack of a bit of sparkle at the top". No, more would not be right, because it is so right! I attribute that to the wood cones he was using - not my favorite tweaks.

By "lighter" I don't mean tonality, which is spot on; I don't mean microdynamics, which it has in spades; I don't mean lack of heft, the midbass and bass are all there. What I mean is: there is no excess baggage. With Nick Cave's The Boatman's Call, I usually listen to the last few tracks. This time, in almost every cut I discovered new nuances in the vocals as well as the instrumental flourishes. The last cut, Green Eyes, popped open mine. I have heard this CD many times, but I was still surprised by the separation between Cave's singing and overdubbed recitation, one in the back and one in front. Each is in its own space, no smearing. It was so good I went back to hear the first cuts. The same phenomenon happens in Save The Children, which also has similar dubbing, from Marvin Gaye's What's Going On: it has never been easier to separate the two. On Van Morrison's Astral Weeks, the guitar strumming is almost real! Now, some of the effects are due to the system, in particular the highly articulate bitstream Micromega Stage 2 CDP (review to come). To give you some idea: the Motown does not in this system sound like it is played by a quality tube amp driving the JBL 4343 (that actually would be lovely) but my smaller system still displays that almost relentless groove of Motown to perfection. If the system were a curry, it would be Thai Green Curry, not even Thai Red Curry, and definitely not Indian Vindaloo (which I love BTW)! A food comment: my mother, a devout budhist, for the last 3 decades of her life, was vegetarian, and I could also eat very little meat. I always say, there are only 2 ways to go for vegetarian: Chinese or Indian (including South Asia)! Well, not entirely, I do like a Quinoa Salad. Come to think of it, Middle Eastern Mezze are great too! Ah, I am hungry!

More on excess baggage. Welcome to the tube world! Start from the basic preamp or amp, there really is no fixed rule on the value of the coupling capacitors. Too small, and the sound would lack heft; too large, and the sound would get sluggish. There is a cost to everything. Take tube rolling, Mullard (in general) is the best example of excess baggage. While some like the sweetness, others like me and audiopro feel things just become blurry and slow. With choice, judgement becomes important. Again, those who view tubes as tone controls may not warm to the Yamamoto, which is antithesis to preamps that are more colored and heavy handed, from the likes of "classic" Conrad-Johnson, ANUK and Jadis, to cite just a few.

Tube Rolling Tube rolling has an effect on the sound, but the fundamental character is unchanged. Telefunken I got some strong ones. The sound at first seems a little more detailed than the US tubes, but one finds out that is because while it seems to have a little more air on top it is a little lean from midbass down, so I prefer the US tubes for the better tonality from midbass down. This I must say happen to me often. For daily listening I use mostly modern components and my systems, though tubed, are neutral in character. What I am saying is, it is not always wise to use Telefunken in modern gears - it depends. When using vintage gears, however, Telefunken's often can be beneficial. RCA Mine have round getters. They are almost as airy and resolving as the Tele's. They seem to be particularly punchy. Sylvania These have D-getters. Sound is even warmer and just a little less in resolution. Western Electric 403A My samples are from the 50's. Boy, this tube sounds substantially different from the others. It made me re-listen to all the tracks. This tube definitely is more midrange-centric. There is less treble air, making Van Morrison's undulating guitar strumming stand out less. But the modulation of voices gains significantly. audiopro would easily pick it out when the singer shifts from using a part of the body to another. Marvin Gaye's singing becomes more soaring, indeed majestic. The back-up singers become more real. So do the cymbals and piano, because of gain in texture. I think I'll use mostly the 403A, but change to RCA and Sylvania once in a while.

vs other Preamps As I just came off the Schiit Valhalla 2 (here), you may want to know what's the difference. Well, it's subtle yet substantial. The OTL Schiit has much less gain and is more literal in comparison; the Yamamoto comes across as significantly more refined and nuanced, indeed possessing a je ne sais quoi quality that delights me! I did not do a comparison with the Shindo Monbrisson, but I know the Shindo is more gutsy, ballsy and bassy (but not in a heavy handed manner, in contrast to the other preamps named earlier).

Triode vs Pentode In SE amps I am positive the pentodes, even if run as triodes, and good as they can be, do not approach the direct heated triodes (particularly in presence). But in the first stage(s) of amplification, I am not so sure; here some of my favorites use pentode/beam, witness Western Electric, Wavac and Yamamoto. There is a large crowd following the all-triode dogma, but I believe that is too narrow, as a mix can yield miraculous results.

Caveat In this preamp, the lack of a balance control is a minus. The reason is more pertinent than usual. Perhaps because of the simple circuit, gain difference between the 2 tubes can be easily heard as a shift from center. Two tubes that have similar readings on the tube tester can have different gains in circuit. This is much more dramatic than most preamps using double triodes. So, aside from having matched tubes, pay attention to the center focus. It is impressive that the 2 stock Tele's that came with it maintained the traction despite the weakening, but my sympathies lie elsewhere.