Preamble: Ray Samuels was kind enough to give me the chance to do a review of the A-10 Thunderbolt II tube preamp/Electrostatic headphone amp. Of course I was very happy to oblige, as it gave me the opportunity to audition a serious Electrostat set-up, which I had never done. As such, it was actually a difficult review for me in some ways, since I do not own, nor have I ever owned, any electrostatic headphones or amps. I have only heard them at meets. So I have no direct reference point. As such, my comments on the A-10 as a headphone amp are really more comments about it in combination with the HE Audio Jade and Sennheiser HE90 together – there isn’t any way for me to separate them. As a Headphone amp, the A-10 is for electrostats only – no provision is made for dynamic headphones. I was, however, able to test the A-10 more fully as a preamp – in place of and in comparison to my Krell KAV-250p, driving my Sunfire Signature amp (balanced) and my B&W Nautilus 800 Signatures. This allowed me to get a very full measure of the A-10 as a preamp. Unfortunately, the comments I will make as about the A-10 as a preamp will not necessarily apply fully to the headphone amp function, as they use different sets of tubes. The preamp section uses two 6SN7’s for gain. The headphone section uses four 5687’s to drive the electrostatic outputs. Common to both are a pair of 12AX7 driver tubes, and, when using unbalanced inputs, a single 12AX7 used as a phase splitter to derive a balanced signal from the unbalanced source. So, dear reader, you have to view my comments within that context. What I will say about the A-10 driving the two ‘Stat headphones is really a “system” review, and my comments on the A-10 as a pre-amp are really only complete valid in that exact application. Pics: Other comments: The A-10 is beautiful, and extremely well built (as you can hopefully see from the pictures above). It is physically VERY large, with its two full-sized chassis, and of course the top-mounted tubes require some careful placement strategies. But it’s very attractive, and the kind of thing an owner will want to look at and show off. It should be noted, although is probably inconsequential, that you cannot use the A-10 for headphones and as a pre-amp at the same time. There is a switch – you choose one mode or the other. Sound: I’m going to have to seriously investigate a Electrostat set-up. It’s impossible not to be impressed. The speed, the clarity, the imaging – no dynamic headphone is capable of what I have heard from the A-10 driving either the Jade or the HE90. I always resisted ‘stats for the exact reasons this review is tough – they require a special ‘stat capable amp, not a normal headphone amp. But this experience has led me to believe this is a step I really need to take. I don’t think it’s possible to get what I heard from the A-10 and its stat headphone pals with any dynamic headphone rig. Certainly the A-10 is a better sounding amp than I had available to try with the Senn HD800, but I don’t think the A-10 alone, if it were wired for dynamic headphone use, would make the HD800 sound even as good as the HE Audio Jade, much less the Senn HE90. It is the combination of A-10 and Electrostatic headphone that was so very addicting. Detail delivery that is completely absent of an aggressive treble presentation was one of the most amazing traits about this set-up. On “Why I Am” from the latest Dave Matthews Band album, some VERY subtle details I had never heard before were quite evident, and yet the treble was never in your face – in fact it’s unfailingly smooth. As a matter of fact, I found listening to “Big Whiskey and the GrooGrux King” via the Jade and A-10 so enthralling that I actually started to like the album a lot, whereas on my first listen to it, I didn’t care for it all that much. Fascinating. The resolution was absolutely good enough to tell the difference between normal 16/44.1 digital, and the effects of upsampling both to 96K and 192k! This was astonishing. Certainly this is far more resolution than the Music Hall’s own headphone jack revealed via the Sennheiser HD800 or any of my Beyer cans. The A-10, for its part, certainly provides terrific sound for both of the ‘stat headphones I used. It drives both with great prowess – astonishingly deep and powerful bass (especially in the case of the Jade), and a lush yet incredibly delicate midrange, and a treble that is so smooth it really has to be heard to be believed. I’ve really just never heard anything quite like it. I distinctly recall hearing several Stax setups and not caring for some part of their performance, but I had no complaints here at all, except to say that I wish I owned this stuff! I wish I could comment more on the A-10 as a headphone amp, but as mentioned, other than to say it sounds truly great, I cannot make any meaningful comparisons. It was the some of the best headphone sound I have ever had in my home -- that much I can say. I am lucky to have been able to live with this rig for several weeks. It’s not for the fiscally conservative - $1,500 headphones (HE Audio Jade) driven by a $5,500 amp – a very significant investment. But it sure sounds good! As a Preamp: Here is where I was able to make some qualitative assessments about the sound of the A-10. I put the Thunderbolt in my main speaker stereo, in place of my Krell. The Krell is, of course, a solid state amp, although fairly smooth sounding. While it’s about 10 years old, I’ve considered it to be so neutral and extended that I have never thought it should be replaced. It also images very, very well. But the A-10 beat it to a pulp in almost every respect. It was more dynamic. It had tighter, deeper, and more powerful bass. It had a lusher, yet more transparent midband. Treble was smoother, but just as nuanced. It had better image specificity (although the soundstage was not as wide as with the Krell). And on, and on, etc., etc. It’s actually not that much fun to review a piece of gear that destroys the one you own, especially since I can’t really justify spending the $5,500 that the A-10 commands. I should also note that this was using Amperex 12AX7’s and Raytheon 6SN7WGT’s – so a not inexpensive tube complement, either. But the A-10 is simply a much better sounding preamp than the Krell. And that is really saying something – the Krell is a very, very good preamp. One of the most interesting things is that the A-10, a tube amp, was actually QUIETER than the SS Krell. This was a bit of a surprise to be sure. But there it was – a real silent runner. This was a great help when playing high-res SACD’s, DVD-A’s, and vinyl – it helped greatly with detail retrieval. The Krell is a real detail champ, and I didn’t think the A-10 beat it here – but it was just as good. It is fair to point out that when it was new, the Krell was $3K. The A-10 is almost twice that. Some will say that isn’t a fair fight, and maybe it isn’t. But at least it’s a reference point – and the only valid one I really had, in this case. The Picking of Nits As good as the A-10 is, I do have a few nits to pick. As mentioned, the Thunderbolt uses the 6SN7’s for the preamp, and shunts them to ground when it’s used as a headamp. Conversely with the headamp and the 5687’s. But those tubes are *on*, and being “used up” regardless of what mode is being used. So the whole time I was using the A-10 as a headphone amp, I was putting hours on a pair of vintage Raytheon 6SN7WGT’s that were not being used. Seems unfortunate. And I guess there is nothing to be done about it, but the A-10 is HUGE. Dual chassis, on big spike feet. It’s superbly built, and very pretty to look at, but it’s big. I had remove components in order to get it in my speaker hi-fi – it takes up the space of both my Krell preamp and Darkvoice headphone amp combined. In Sum This isn’t the most comprehensive review I have ever written, because the A-10 is a unique product. Without other electrostatic amps to compare it to, I feel I have done a less than complete job with it, and for this, dear reader, I apologize. But rest assured – the A-10 is a terrific sounding amplifier, albeit a very expensive one. If you’re an electrostat owner and lover, though, I cannot imagine that the A-10 wouldn’t excite you. I found it thrilling to listen to. Sorry I’ll have to let it go.