All of which means that while tube failure might be an inevitability, the S-400 makes it about as mundane an experience as it’s possible to be, a stark contrast to the drama and fireworks (I use the word advisedly) that can accompany tubes failing in other company’s amplifiers. No loud bangs, no smell of burning components attached to the valve base, no smoke, no fire and no expensive and inconvenient trip back to the manufacturer for repair – which is just as well given how difficult the S-400 is to shift! In addition, the amplifier also monitors its internal operating temperature, the incoming AC voltage and the operation of its own power supply, to ensure that it doesn’t suffer associated damage. It even reminds you when it comes time to swap out your tubes. This amplifier is auto-biasing, self-checking and self-diagnostic. Combine that with a fully regulated, unconditionally stable, global feedback free circuit and you have an amplifier that doesn’t just deliver great power and great sound, it does it reliably and in an utterly fuss-free manner too. These days, other auto-biasing tube amps are starting to appear, as are tube timers and other niceties. But just remember that the S-400 II is over 10-years old. Operationally, it was WAY ahead of its time and, in many ways, it still is.
Which brings us to the numbers. The S-400 puts out 300 Watts into an 8Ω load. The Mode button on the front panel allows you to switch it to triode operation, in which case it outputs 150 Watts – although why anybody would do this escapes me. If you want a triode amp, buy one that actually uses Triode tubes. Why does the amp offer a triode mode? Because the market expects it: go figure… The output transformer is optimised for a 5Ω load that covers loads between 4 and 8Ω with stability down to 2Ω. There is no high impedance tap provided. Incidentally, the third front panel button is a mute, which is handy. The same size and shape as the flagship Siegfried mono-bloc, the S-400 actually weighs more than its big brother, down to that second output transformer. 113kg/250lbs to be exact, making this about as much amplifier as I’m prepared to deal with on my own – and then only as a result of considerable experience, specialist tools and a few tricky techniques I’ve developed over the years. Fortunately, the height of the amp and the hand-holds that are provided once you remove the top cover do ease the challenge somewhat. However, if you find yourself looking at an S-400 that needs moving, do yourself a favour – get help, at least with the heavy lifting!
That aside, the Making Tubes User Friendly claim certainly holds water. I have not come across any other high-powered tube amp combination that is as elegant and versatile in use, as reliable and fail-safe in operation. All of which is great. But what really sold me these amps was the way they sound – and the fact that they sound that way almost irrespective of partnering speakers.
Sound per pound…
There is clearly no direct correlation between the weight of a product and the way it sounds (at least at the upper end of the scale). However, taking technology into account, it can be suggestive. In the case of the S-400, it adds up to a lot of transformer and a really, really big power supply. Unless you missed it earlier, this is a fully regulated design. It’s also fully balanced up to the output stage, which is push-pull in any case. That puts it in a pretty small group – a group that get’s smaller still if you confine it to tube amps. The S-400 and its mono-bloc twins, the Siegfrieds, really are amps apart. They are also amps that, along with the TL-7.5 and 6.5 line-stages have been, in one combination or another, constant companions on my audio journey for the last decade. In that time, they have been the centrepiece or context for many an instructive experience. I have followed the evolution of these products and used them as the backdrop to assessing others. In that time, the TL-7.5 and S-400 have formed the benchmark against which VTL’s MB-450, the (seriously under-rated) MB185 and Siegfried mono-blocs have been measured, along with the one-box TL-6.5 and TL-5.5 line-stages and the TP-6.5 phono-stage. They have been used with a host of different speakers, most notably the Wilsons (Alexx, Sasha 2, DAW and WatchDog and Thor’s Hammer subs). They have been a core part of one of the most enjoyable and engaging systems I’ve had at home: the TL-7.5 and a pair of S-400s was used to run the Sasha 2s with the WatchDogs, to considerable musical effect. And therein lies a tale.
