I once bought early Hypex class D amplifiers and found them to sound colored in the mid range. Not anymore, they say, and lent me a set of Hypex NC400’s to try. The NC400’s come in kit form. Not that you have to mount components on the PCB but more like an assembly job: you have to screw in two fully assembled PCB’s, the amp module and the power supply, connect some cables to it and screw, solder and clamp them to the connectors on the rear. You find a video on Youtube showing the assembly when you click on the link in the top right corner.

The assembly is easy and soon you have two very nice looking mono power amps. They each measure 28 by 20.5 by 8 centimeters and are made of sturdy black anodized aluminum. The front only contains a blue-white LED to indicate the power is switched on. This LED can be dimmed or switched off all together, something all equipment should have when using blue LED’s. Once built, the rear has one balanced input on XLR, a set of proper speaker binding posts, an IEC power input with fuse holder and a power switch. Some tech As usual you can skip the tech by jumping to the timecode in the top left corner.

OK, let’s first talk about class D and the misunderstanding that class D is about digital amplifiers. Class D amplifiers are a special kind of analogue amplifiers that use pulse width modulation or pulse density modulation techniques. The first works by switching on a voltage on for a variable time. The longer the voltage is on, the more positive the output becomes. Pulse width works almost identical by switching on more or less short voltage pulses. These are very efficient techniques since there is hardly any current flowing so there is no heath building up. It is a very common technology nowadays and for instance switching power supplies are based on the same principle. To explain it in a metaphor: if you want to drive a nail into the wall, you could do that by applying a very high force that pushes the nail into the wall. But you would need a very powerful device that needs to be secured firmly.

You could also use short pulses of kinetic energy, as thee ones stored in a hammer when you slam it on the nail. Come to think of it, a combustion engine, like the one in your car, does the same. In a four cylinder engine there is a short combustion every half revolution. The mass of the flywheel evens out those short bursts into a constant rotating force. It’s about the same with class D: the short pulses are dampened by the electronic equivalent of the flywheel: a low pass filter. One of the problems that occur when designing a class D amp is that this output filter is normally influenced by the electrical properties of the speaker which are far from constant. It is one of the problems design genius Bruno Putzeys has solved. And there are many others that makes the NC400’s what they are, including a clever switching power supply that proves that switching power supplies can sound very good when designed well. I didn’t fully measure the NC400’s since measuring class D requires special filters that I don’t have. Those things I could check, gave no reason to doubt the other specs by Hypex.

The amps can produce up to 200 watts in 8Ω, 400 watts in 4Ω and 580 watts in 2Ω. Often amplifiers die when connected to a 2Ω load! I am always interested in the current an amp can provide: the NC 400 is protected at 24 amps! All and all: you’re not likely going to find a speaker that can’t be driven by the NC400’s. Another remarkable fact: the switching power supply can be connected to any mains voltage up to even 264 volts – which isn’t likely to happen – and automatically switches to the correct setting for optimal efficiency. Typical working voltages are of course 230 and 110 volts but even 180 and 90 volts they should run properly. I used the Arcam AVR600 in absolute analogue mode and the Marantz Pearl KI as pre-amps, the Chord Hugo, driven by the Sonore microRendu and Roon as player and the Audiophysics Scorpios as speakers.

The first day the sound was uninspired, badly timed, glassy, unmusical and really terrible. Not in the way the old UcD400’s were, but just like many amps sounds when playing for the first time. It took a few days to have it bloom a bit, improving bit by bit every day. Only after two full weeks there was no further improvement. The Scorpio speakers aren’t difficult to drive. They are normally driven by a 2 x 13 watt modified Audio Note Soro SE tube amp. It’s therefore no surprise that the low end, taken care of by two times two opposite from each other mounted 18 centimeter woofers, became more controlled using the Hypex amps. The mids and highs were less refined than those from the Audio Note, which is no surprise given the roughly 6,000 price, including mods. Comparing it to the Marantz KI Pearl Lite that, as an integrated amp was € 1,200, again brought the impressive low end control of the Hypex to the attention while I would rate the mids and highs at a slightly higher quality, although more forward. That places the NC400’s somewhere between my Set 2 and Set 1, somewhat closer to Set 2. By offering these amps unassembled the price could be kept low: € 650 excluding VAT which means about € 770 including VAT in many European countries.

That really is a very attractive price for a pair of 200 watt in 8 Ω amplifiers of this quality. The assembling only takes a few hours or less but make no mistake since you’re not allowed to open them again, according to the label on the back. OK, that was cheap too. To be serious: the NC400’s have proven to me that class D amps can really sound musically and have high end aspirations. Whether that goes for all class D amps, I can’t say yet. But if you want to stay informed, follow my Facebook or Google+ page or my Twitter account. Or take a subscription to this channel. You can also post questions there but please view my Questions video first. See the link in the top right corner. You’ll find more information below this video in YouTube. If you liked this video, please give it a thumbs up and tell your friends on the web about it.