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Nord One Up SE NC500DM Mk II By Alex Colburn A little over two and a half years ago Colin North of Nord Acoustics launched the Nord One Up NC500DM dual mono stereo power amplifier and One Up NC500MB monoblock version. Nord’s NC500 family of amplifiers are based on the Hypex Ncore class D technology and capable of delivering 400W into an 8 Ohm load. One of the keys to the amplifier’s excellent performance was the Nord designed input buffer incorporating Sparkos discrete regulators on the power supply and a variety of user selected dual discrete class A op amps from Sonic Imagery, Sparkos or Burson rather than the Hypex designed monolithic amplifier. Discrete op amps are used extensively in professional audio due to their superior performance in terms of sound quality, noise and output current. On the face of it, using a class A amplifier to drive a class D output stage seems counterintuitive but the combination works very well. At the time of its launch, George 47 did an excellent review of the original amplifier that is available here: https://www.hifiwigwam.com/nord-one-up-500-dm-st-dual-mono-stereo-amplifier-review/ More recently, Colin has launched a new family of One Up NC500 amplifiers under the Mk II guise. The new range features a completely re-designed buffer board designated Rev. D. You don’t need to buy a new amplifier the get the latest spec, all older amplifiers can be upgraded either as a DIY installation or a return to base if required. The new board moves away from the original dual op amp design and utilises a pair of single discrete op amps based on a design originally developed back in the 80’s by Deane Jensen of Jensen Transformers for professional audio use and utilising a much larger pin footprint than the standard dual-in-line devices. Moving away from the dual op amp topology has some technical benefits, cross-talk inherent to the dual devices is eliminated and the single devices have considerably higher class A output drive capability. The heat sinking of the Sparkos discrete regulators has been beefed up to cope with the increased current demand. In addition to the use of audio grade polystyrene capacitors throughout, the new topology has allowed fine-tuning of the supporting circuitry and improved noise and RFI counter measures. Nord offer two op amp options for the Rev. D board, the Sparkos SS2590 which is a naked PCB device and the Sonic Imagery 990ENH which is fully encapsulated. Differences between op amp options on the Rev. D board are apparently less than found with the Rev. C board offerings according to Colin but some may prefer one over the other. As a fan of the Sonic Imagery 994ENH op amp in my Rev. C boards, I opted for the Sonic Imagery 990ENH in my Rev. D boards. Nord Rev D buffer board In light of the excellent performance of the original Mk I amplifier with Rev. C buffer, my expectations for the Mk II were relatively modest but I ended up being proved completely wrong on that point! Before undertaking any critical listening, I allowed the amplifier to run up to a stable operating temperature over a little more than an hour. Starting the audition with my usual collection of well-loved favorites, it quickly became apparent that the Mk II amplifier was giving me a significantly more expansive and precise soundstage. Both artists and instruments are presented in a rock solid 3-dimensional image. I’ve used the optical analogy because it’s like viewing a larger, sharper image. The audition continued largely playing tracks I knew imaged well as I wanted to explore how good it could get. After many tracks, I was convinced the Nord Mk II was getting the very best from any spatial and ambience content in a recording in as much as the Glastonbury Tor speakers were capable of reproducing. Moving on, the Mk II retains all the great qualities of the original and adds to that an improvement in dynamics. Faster edges to bass notes add texture, authority and weight to the bass, notes start and stop as they are supposed to. I find a good measure of a system upgrade is when it spurs you on to playing music you previously shied away from and the Nord Mk II certainly did that for me. The net result is to move the recorded performance that bit closer to the live experience. Class D has come of age and is here to stay, all be it with the assistance of some class A magic from Nord! If you are a Nord One owner with the Rev. C buffer boards I can only recommend you upgrade to the Rev. D boards, it’s well worth the cost IMHO. Upgrade prices start from: £658.80 including VAT for a stereo pair. Associated review equipment: Source: Linn Klimax DSM Mk 3 Speakers: Modified Townshend Glastonbury Tor Mk1/Townshend Maximum Supertweeters Interconnects: Nordost Tyr 2 balanced XLR Speaker cables: Nordost Heimdall bi-wired Z-plugs
With the release of the new Linn streamer models some have integrated class D power amps! For some time Linn have held the view that class D was an immature technology and not suitable for use in their amplifiers, so they must clearly think class D has come of age?