I've had a pair of Nord NC500 MB monoblocks for about 7 weeks now and thought it may help to share my experience.
I had been using a Benchmark DAC2 and Bryston 4B SST driving PMC OB1i speakers. This is all pretty good, mainstream stuff, but I felt that the Bryston was a tad 'hard' and analytical. I auditioned the Atsah equivalent at The HiFi hanger and frankly was amazed. Admittedly they were using better speakers than mine by the musical insight was a revelation. They played me a variety of tracks and every one sounded better than I could hope to get at home. Even allowing for his excellent panel speakers there was obviously something about those amps that was well worth investigating. As they were reluctant to let me audition the Atsah amps at home I gave the Nords a try - and they were cheaper which always helps.
Doing a comparison against the Atsah amps is pretty well impossible as I listened in different rooms to different speakers and to different music. I will say however that both the Nord and the Atsah were instantly impressive and excellent value. At home, the £1,400 Nords were taking on the £5,000 Bryston and and still sounding good.
Having read the reviews on the Burson web-site I had the Nords delivered with Burson op-amps. and compared the Nords carefully against the Bryston for a week or more. After that time I was convinced that the Nords were more musical than the Bryston BUT less detailed, less dynamic and frankly the Nords made a mess of complex orchestra crescendos whereas the Bryston just got on and played every detail that you would expect to hear. A clear win for the Bryston and I talked to IQ about returning the amps.
'Hang on a minute', they said, 'please try the Sparkos op-amps before you send it back'. So I did.
Fitting the new op-amps is dead easy and takes about 5 minutes per amp working slowly and carefully.
With the Sparkos op-amps on place, there was no need for warming up or running in, it was instantly better in every regard. The Nords sounded even more musical, the missing detail returned in a very relaxed and easy manner and suddenly the complex orchestra work was sounding like real music, not just hifi. Rather like I found with the Atsah amps, the Nords now sound musical right across the board regardless of what music you play. They don't scream 'DETAIL' at you but instead sound like real music which doesn't have to make an effort - because it just 'is'.
A few weeks on and every time I put on some music I am instantly transported into the music instead of listening to the hifi. That is what it should all be about in my opinion. I don't want hifi, I want music - and that is what I have got from the Nords.
The Bryston amp is still a little more dynamic than the Nords but I much prefer these amps to the Bryston. That makes the Nords pretty good value for money. In fact I sold the Bryston for more than the Nords cost so I got a free upgrade and some spare money to buy some more music.
One interesting point. IQ tell me that some people much prefer the Burston to the Sparkos op-amps. Maybe this is a matter of taste or maybe it is related to the interaction with the rest of your equipment? Whatever the answer, if you try these at home and don't like them, for goodness sake do try the other op-amp option.
Lastly, the standard of construction is good but not really world class. Compared with the Bryston, for example, the construction is almost crude but the Nords are plenty robust enough and have the advantage that they can be tucked away out of sight so long as you set up some sort of remote power supply. I made up a couple of relay driven sockets so that they would both turn on automatically with the pre-amp. Well worth it if you are a lazy sod like me.