So it's time for an update on life so far with the NJC pair.
Well it didn't get off to a good start. I didn't notice it at first but shortly after writing the review above I found that the amplifier has a fault where it works fine for about an hour then the right earphone suddenly cuts out and goes silent. If I switched it off for half an hour then try it again it continued to work fine for about an hour before cutting out again.
So I contacted Nick at NJC to ask his advice. He was surprised to hear from me as all their products have been extremely reliable so far but he was very friendly and helpful nonetheless. Even though I'd bought the amplifier second hand and it was past it's 3 year warranty (by just 2 months) he suggested that I post it to him and he'd take a look at it. When he received it he spent two days continuously running it under load and taking measurements but as far as his tests were showing everything in the amplifier section was still functioning perfectly.
After hearing this it occurred to me is that when one ear cut out it was very hot in my room which receives a lot of direct sunlight and can sometimes get uncomfortably warm in the summer. As the issue only happened after it was running for over an hour but went away again once it was switched off it might possibly be a temperature related problem? Maybe something is expanding and contracting causing a bad connection somewhere?
I mentioned this to Nick who then placed the entire amplifier in a process that heats it to an ambient temperature of 53C. They usually only perform this on prototypes since this temperature is beyond anything found in a normal environment but it does highlight any thermal related issues. However, the amplifier continued to function perfectly with not a single problem over a two hour period.
The only thing left that it could be was a damaged headphone socket. IMO this is far more likely to have been damaged by the previous owner being heavy handed when plugging his headphones in rather than it being a fault of NJC. The socket they use is of the highest quality available and the rest of the amplifier itself is in mint condition apart from a tiny sign of wear at the headphone socket. So Nick very kindly replaced the headphone socket free of charge and posted it back to me.
Wow! I mean really. Wow! (I remind you it was bought second hand, it was past it's 3 year warranty and the fault was most probably due to damage caused by misuse rather than a fault with the actual amplifier itself).
That's really great customer service backed up by good communication letting me know at every stage what was happening. In fact the service I received from NJC is the best that I've ever come across in my entire life. If anyone is ever considering buying something from NJC do so with upmost confidence. They' re excellent to deal with.
Oh and how does it sound now? Well I've had it back for two days and it's been playing continuously for several hours on both days without any issue. It's fixed and it sounds brilliant!
I haven't done a direct back to back comparison to my O2 amp so this may be my imagination here. But I'd swear that the NJC controls the bass better on my HD700s than the O2 does. Either way, the NJC sounds perfect in every respect and I'm over the moon with it.
Thank you very much Nick for your help.