This is a review and detailed measurements of the Nord Three SE 1ET400A Dual Mono Stereo Amp with the optional Sonic Imagery 990Enh gain stage. With that option, the cost is £1,979.00 excluding VAT. This translates into US $2,554. The unit was purchased new and drop shipped to me by a kind member. I had previously measured the reference design from Purifi so will be good to see how this version rates with a different input stage.The Nord dual monoblock comes in a very attractive enclosure (most of which is not visible in this image):Efficiency of class D amplifiers and switchmode power supply enables such slim case to be used. There are two rows of heatsinks on the sides but they are decorative for the most part. I will do a teardown separately. For now, the amplifiers dissipate heat into the bottom of the chassis and dual power supplies have their own heatsinks inside the box.The back panel shows seriously beefy and nice feeling speaker connectors:When I received the unit, it immediately shut down. The reason was a blown fuse. I replaced it with a spare that comes in the IEC holder. That worked for all but my last test which is the strenuous power vs frequency. I have let Colin know that I think the fuse amperage needs to be increased given our low operating voltage in US. Note that with music you are not going to hit this easily so it is more of an issue of lab/stress testing. I don't have a higher amp fuse to try with it until a batch arrives on Monday. The fuse is the smaller 5x25mm which I only have a few of in low amperage (usually are used in multimeters and such).: turns out the fuse that was sent for was for 240 volt countries. A "slo-blow" 10 amp replacement fuse was sent and worked fine.Other than this, the amplifier was solid in its performance never shutting down or complaining. The enclosure didn't even get warmer than room temperature. Inclusion of two power supplies here relieves my worry of a the power supply being the weak link, not the amplifier.As usual we start with our dashboard of 5 watts into 4 Ohm at 1 kHz:This is right on the money as far as THD+N and hence SINAD:Which is great news of course.Noise performance also matched the Purifi reference design:We have a very low distortion and very low noise floor. This is all that you would want to ask an amplifier. That, and power so let's see how it does there:Dual power supplies don't give you more power as we are essentially matching the reference design with one power supply.I was surprised to see a rise in distortion with one channel worse than the other. Is this the Sonic Imagery 990Enh gain stage in play or were we given better evaluation samples at announcement? We won't know until we test another amp that uses Purifi gain stage.Same issue exists at 8 ohm although not as exaggerated:This makes me think the issue may be in the amplifier.Note that this is not an audible concern so don't jump off the cliff please.We see an exaggerated version of the same in intermodulation distortion relative to input level:Frequency response is flat and similar to reference design:Sweeps of power versus frequency gives us varying curves (ideal = all curves on top of each other):We see that at 20 Hz where we need most power, we have least amount of it. This is typical of amplifiers since 20 Hz tone changes slowly not giving a chance for power supply capacitors to recharge between cycles.Finally here is the 19+20 kHz at the same 5 watt power of Purifi reference design:The pair around the main tone are identical to reference design. Noise floor is a hair higher but that is probably run to run variation.The Nord Three SE 1ET400A Dual Mono Stereo Amp is an attractive build of the Purifi class D amplifier technology. The dual mono configuration raises the price fair but but my belief is that it will last a lot longer than the single power supply version. Measured performance is just a bit worse than Purifi reference design as power increases beyond 25 watts or so. Not an audible difference but would be good to figure out where this is coming from. I can't detect any improvement from Sonic Imagery discrete 990enh opamps. So personally I would go with the stock gain stage and save enough money for a night out alone.I am happy to recommend the Nord Three SE 1ET400A Dual Mono Stereo Amplifier. It builds on state-of-the-art Purifi amplifier modules and delivers it in nice packaging.--------As always, questions, comments, corrections, etc. are welcome.The Pink Panthers are making up their Christmas list and I can tell you it is going to be a long, long list. The have become sophisticated enough to create their lists on Amazon! One has been daring enough ot put in Caviar for heaven's sake! I am going to need money and lots of it. So pleaseusing : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/