Building a Hypex UcD700-based power amp

Usually when I have compared power amps, the differences have been so small that I've been forced to concentrate hard to be able to characterise them. This was not the case in comparing the 'Node-Hypex UCD700', the Node Audio Mosfet and NAP250. The differences were large, obvious and interesting.

We started with the 250, as this is an amp that we've both heard on many occasions, usually in my Impulse H6 based system. In this system, it sounds detailed, exciting and something I've happily been able to live with for many years. Plugging it into this system wasn't what I'd call a huge disappointment, but it certainly didn't sound desperately happy. Its hard to explain exactly why. It sounded a bit soft, but to my ears was quite detailed and not a million miles away from what I was expecting. But what it didn't have was any real sense of music to it. It was just a bit boring really - not unpleasant but not really making enough of an impression to make me want to listen for very long. Now my 250 is pretty old, and I remember it sounding stunning in my old Sara based system, so I'm not inclined to condemn the 250 as a Sara driver - I suspect mine needs some fettling, though note it stills sounds good driving the very easy load of my H6s. One thing I did notice was that pretty much every piece we played through the 250 sounded much the same - good but not that good. I remember my friend commenting that Wings sounded a bit like a poor tribute band and I can see what he meant. Dull and lacking in sparkle is how I'd summarise.

On to the reason for my visit, the newly completed and still running in UCD700 amps. These are absolutely huge. Believe me, you get no real sense of the size of these from the photos. They are also a 2 man lift, so on domestic acceptability grounds I'd mark these as "null points". My wife, on first seeing them did the pursed lip thing followed by "Where are you planning to put them, then.."

Anyway, first track which I think was Ben Sidrans "Bop city" and bloody hell these are incredibly fierce and in your face. It is immediately obvious that whatever you may think of them, I can't imagine anyone not having a strong opinion of some sort. We played loads of tracks, with the sound seeming to change over the course of the night - mains, running in or hearing damage I'm not sure. So the following summary relates mostly to the sound that I was hearing at the end of a couple of hours worth of listening.

First off, I'd have to say that on the most important measure, these are far and away the best power amps I've heard. What they do is simply compel you to listen to the music, and get you thinking "I wonder how Joan Armatrading/Willy Deville/Goldfrapp/Art Pepper/Ben Sidran etc would sound. They had my feet tapping in a way that they haven't tapped for a long time. I don't know why they do this, but they just convey the drive and urgency of the music in a really compelling and convincing way.

Thinking about some of the elements of the sound that really leap out, firstly they are exceptionally detailed. I've listened to "Total Control" by the Motels hundreds of times, but the Hypex delivers the sheer desperation in the singer's voice in a way that I've never heard before. As a bad (that's bad as in not very good by the way) saxophone player, I'm fairly sensitive to the tone of a tenor, and again this amp delivers a sax sound with edge, and breath and bits of spit dribbling around in the mouthpiece - it's startlingly realistic on the right material. And I've never before noticed that Art Pepper is really having to work on his breathing on "Art Pepper meets the rhythm section". So on the clarity and detail of the sound I'd have to give the Hypex top marks.

Next, control and coherence. Hmmmm, I'm in a bit of a tricky position here. The UCD700 is absolutely in control of things. In fact it's so in control of things that it's a sound that I'll take a while to get used to, and to accept as correct. This is particularly easy to explain with respect to how it handles volume. No matter what volume its played at, it sounds pretty much the same. With other systems I've had, there's always been an optimum volume for listening, that is a volume at which the music suddenly comes alive and starts to sound right. This doesn't happen with the 700 - in fact its quite hard to detect increases in volume at all.

All that happens is that at some point your ears start to hurt and you realise that you can't hear yourself talking at all. I'm sure that this is how an amplifier should behave, but its very odd when you've spent years using distortion as a cue for the perception of loudness. Anyway, this control doesn't just extend to loudness - it's in every aspect of control that you can think of, whether starting and stopping on time, debloating bass, absolutely everything. The Saras just sounded like they had absolutely no say in things at all - they were going to do exactly what they were told, or explode trying. In fact, I've just realised that this is probably the only time I've heard Saras where the sound of the whole system was not actually dominated by the speakers themselves. With the UCD700, it was the sound of individual records which came through rather than the speakers.

Which brings us neatly onto the sound of individual records, which was frankly incredibly variable. Some recordings (e.g., Graceland, Supernature) sounded frankly horrible. Really horrible, like having a pressure washer forcefully fed into your ears while being kicked. The 700s delivered a sound of such penetrating driving clarity that it was hard to listen for too long. Maybe this will soften up a bit as they run in, or maybe this is just how these albums were recorded. But on the right material, by which I mean either good acoustic stuff such as live jazz, or competently recorded more modern pieces like the Brand New Heavies' "Shelter" or Stevie Ray Vaughan's "Couldn't stand the weather", then the sound was refined, detailed and just astonishingly involving and fun. It's a bit difficult to know what to make of this - do you buy an amp that makes everything sound the same but inoffensive, or go for something like the UCD700 which I think is probably telling it like it is but which can disappoint on some recordings. I think the latter.

Just to check that we weren't getting carried away, we tried a final control of the Node Audio Mosfet monoblocks, currently in the process of being rebuilt by the 'factory'. I can summarise this very simply. These to my ears sounded like a better version of my old 250, but were obviously the same family of sound. Yes, they were tighter, more detailed and nicer to listen to than the 250. They weren't categorically different to the 250, just delivered much more and better of the same type of stuff. The Node-Hypex UCD700s on the other hand deliver a sound that is so radically different from other power amps that I've heard that I'm excited by it in a way that I haven't been for years. I'm still not 100% sure about it, but I'd go back to what I said at the start, which is that it simply sucks you in to wanting to play more and more records - which at the end of the day is all that counts.
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