I think we have hashed and rehashed this many, many times over. If there are sonic differences in normal use, it is due to input/buffer stages. They do behave slightly differently at the extremes - the nc400 is more suitable to extremely low impedance loads, while the nc500 can produce more power into a "normal" load.
Hey Julf, do you think you could point me towards a discussion regarding the latter part of your statement if you know where one might be off hand? I too am looking at the NC400 vs NC500 and have what I would consider 3 ohm speakers. I just want to see what is limiting both the NC400 and NC500 at the lower impedance. I am more than happy to read, I just can't find the discussion which I am sure has taken place somewhere in this 1000+ page thread.
Thing is, nobody that we know on this Forum has actually taken both and thrashed them out A vs B (except for Bavmike, a USA OEM who says nc500 is better with his Class A Buffer) ...Certainly no ABX testing as Julf would insist. It's mostly theory 
I'm in West London
Ps. Have had these nc500 ON solidly for 5 days now...
I am starting to think there may be a little something regarding Burn-in and being ON for a period of time because the midrange seems a little warmer and interesting now, not so recessed as initially thought i.e. Vocals seemed to be behind my speakers, almost in the distance...and I was not that impressed, being honest.
Treble still sounds much the same though, can be etchy with my current Source, but at least now I prefer these nCore to my TAG McLaren amplifiers as the image seems wider and more life-like too, notably when I crank them up (thank Goodness for that)!!!
I'm in West London
Ps. Have had these nc500 ON solidly for 5 days now...
I am starting to think there may be a little something regarding Burn-in and being ON for a period of time because the midrange seems a little warmer and interesting now, not so recessed as initially thought i.e. Vocals seemed to be behind my speakers, almost in the distance...and I was not that impressed, being honest.
Treble still sounds much the same though, can be etchy with my current Source, but at least now I prefer these nCore to my TAG McLaren amplifiers as the image seems wider and more life-like too, notably when I crank them up (thank Goodness for that)!!!
No way I am going to wade through this whole thread again
Both specify pretty much the same minimum load impedance (1 ohm) and output current limit 25/26 A, but the crucial difference can be seen in the power specs.
With an 8 ohm load, the nc500 produces 400 W and the nc400 only 200 W, reflecting the higher voltage swing of the nc500. At 4 ohm, the difference is pretty similar, 700 W vs. 400 W, but at 2 ohm the nc400 actually produces slightly more power than the nc500 - 580 W vs. 550 W.
As you can see, the nc500 produces more power into 4 ohm than into 2 ohm, but the nc400 does the opposite, it produces much more power into 2 ohm than into 4 ohm.
Thus the nc500 is more powerful into higher impedance loads, but the nc400 seems to cope somewhat better with extremely low-impedance loads.
People selling 500's will probably point out that the difference isn't very significant with normal loads.
Thanks for the insight, I have done some reading in the 1000 plus plus thread but as you said there is no direct comparison since there is a whole range of op amps to be used in the NC500 which might have great(?) impact on the sound and the NC400 has the hypex own op amp design included in the module.
ABX with NC500 with hypex own op amp (LM4562) vs NC400 would be interesting though...
I am about to upgrade my amps and hypex is tempting. My system is Pioneer LX-86, Parasound P5/A23 combo for stereo and B&W 804S, HTM3 center and CCM664 for surround sound. Pioneer is running class D amps allready but a less epencive one (former LX-series had B&O ICEpower in them).
3xNC400 is 2000 euro and NC500 is from 2250 euro to fully upgraded about 2850 euro.
I am leaning towards NC400 as they better value me thinks...but I would love to get my hands on some NC500 boards incl LM4562 and just make them my self...
ABX with NC500 with hypex own op amp (LM4562) vs NC400 would be interesting though...
I am about to upgrade my amps and hypex is tempting. My system is Pioneer LX-86, Parasound P5/A23 combo for stereo and B&W 804S, HTM3 center and CCM664 for surround sound. Pioneer is running class D amps allready but a less epencive one (former LX-series had B&O ICEpower in them).
3xNC400 is 2000 euro and NC500 is from 2250 euro to fully upgraded about 2850 euro.
I am leaning towards NC400 as they better value me thinks...but I would love to get my hands on some NC500 boards incl LM4562 and just make them my self...
Hi Balgjerd
B&W 800 S series were amongst the brightest speakers I have owned (been through a lot of kit)
In case you are stuck with your Source, having OpAmp or Buffer options may be useful, in my opinion... nCore amplifiers do not mask anything and the rumour of Tubey/Valve-like treble is not so in my limited experience !
It would be interesting to see the 1ohm specs of nc400 and nc500
B&W 800 S series were amongst the brightest speakers I have owned (been through a lot of kit)
In case you are stuck with your Source, having OpAmp or Buffer options may be useful, in my opinion... nCore amplifiers do not mask anything and the rumour of Tubey/Valve-like treble is not so in my limited experience !
It would be interesting to see the 1ohm specs of nc400 and nc500
Only if that is how you want to interpret it. I was genuinely interested in what parameters you wanted to see measured at 1 ohm (as I think the behaviour is pretty well predictable from the specs hypex have already published).
So again I have to ask (and it is not in order to be obnoxious) which specific numbers you are interested in?
That is why I was asking - because in many ways it is the least informative parameter. Let's look at the numbers with a calculator in hand.
The nice thing is that if we assume a resistive load (as manufacturer's specs tend to do), if we know the power and the resistance/impedance, ohm's law tells us both the voltage and the current.
First the nc400. 200 W @ 8 ohm implies 40 V and 5 A, 400 W @ 4 ohm is 40 V and 10 A, and 580 W @ 2 ohm is 34 V and 17 A,.
The same numbers for the nc500 are 400 W @ 8 ohm implying 56V and 7 A, 700 W @ 4 ohm -> 53 V and 13 A, and 550 W @ 2 ohm -> 33 V and 16.5 A.
What do these numbers tell us? As you can see, the output voltage starts to sag at 2 ohms with both amps, but the sag is much more pronounced with the nc500. I think we can see the design trade-offs here.
Remember the current protection kicks in at 25 or 26 A. With a 1 ohm load, that would be 625 or 675 W. Based on the numbers above, I would put my bets on the nc400 getting closer to that value than the nc500.
That was the case with the older generation of class D topology, with a relatively high-impedance choke in series with the output, and not part of the feedback loop.
As the numbers above show, it is a trade-off, clearly the nc500 gives higher power at "normal" speaker impedances, while the nc400 is better at extremely low impedance loads.We might find the nc500 and nc400 being very similar at 1ohm, so the advantage is a boosted 8/4ohm
In terms of absolute power I assume the limiting factor is the power supply, but in terms of maximum current it is probably the safe operation of the switching transistors and choke.
If you would replace the power supply with a humongous power plant capable of supplying hundreds of amps without any voltage drops, and went on to play at full power into a 1 ohm load, I expect the magic smoke would escape at some point.
That is not so easy to specify.
Power transisitors have un upper limit w.r.t. total dissipation, voltage and current, but current demand depends on signal (which is not steady state as we are presumed to listen to music), and heat dissipation plays an important role too.
Easier to specify with class A amplifiers who have high and constant idle current not depending on signal.
For class D amplifiers it is good to have protection for maximum current.
Happy to implement any design that would add further improvement. Ill give him a PM.
Meanwhile been busy all weekend working on the Nord One Pre Amp. This is just a prototype have to sort the display Plexiglas and the infrared sensor. I used a scrap front panel just to try it all out. The Aluminium Knobs are on the way. Next is to add a DAC. So we have a fully balanced output to the Amp and one fully balanced Input plus four RCA inputs a Remote and Home Theatre function.
Meanwhile been busy all weekend working on the Nord One Pre Amp. This is just a prototype have to sort the display Plexiglas and the infrared sensor. I used a scrap front panel just to try it all out. The Aluminium Knobs are on the way. Next is to add a DAC. So we have a fully balanced output to the Amp and one fully balanced Input plus four RCA inputs a Remote and Home Theatre function.