I have had three NAD amps from the c270 era on fail, all for the same reason: terrible thermal management and cheap construction. A bad combo.
Cheap capacitors are packed far too close to heat sinks and other heat sources. The larger Resistors run shockingly hot. So hot that as the c270 aged, a some power resistors on the amp board got so hot the solder melted. The resistors did not smoke, but burned your skin in half a second and heated the traces, etc.
The pcb boards all show areas of severe heat, even in preamp or buffer areas.
The pcbs are the cheapest I have ever seen and traces lift if you look at them. Add any heat stress and they are close to not repairable.
The circuited are very complicated and there are an incredible number of components like transistors, caps, etc than drift due to premature heat aging or just blow.
Never again.
Had a sunfire 2x300 with the class h topology. Great power and ran cold always. Lots of noise from the power supply in tests though I never heard it in use. At least with lowish sensitivity speakers. But when is developed a fault in that power supply it failed with fireworks. Kaboom. The output stage seemed fine but the power supply and regulation to it failed with smoke and sparks. The build quality and layout was also rather amateurish and cheap. For example the huge transformer had “shielding” just hot glued to the top of the el-transformer. No mechanical connection to the case etc. so not much shelling lol. And the input circuitry and speaker out wiring was quite close to the transformer. Nice. the ac filtering to the transformer was a joke…one cap and resistor on a 10c terminal strip screwed into the chassis a cm away from one of the speaker outputs. The star ground was an 18awg wire running across the screw terminals of the filter caps with every other ground wire wrapped around it plus another one screwed to the chassis. Yeah…wonderful.