But heating a single pin and removing it is far easier than all 3 or 4 at once, no matter how tight its stuffed in there.
Whilst our new input buffer board is close to Hypex's Design its no longer on the drawing board, its about a week away from being delivered to customers ears. At a reasonable price, gives them choices to experiment with different OP Amps and requested in response from DiyAudio members. Not to mention sounding very, race through my record collection lovely! 
Considering this thread is now over 900 pages, and includes DACs and motorcycles, just replying with the actual gain number could have been helpful...
I saw the discussion of the 4.5x gain of the NC400 input buffer but not the gain of the stock NC500 input buffer. I will go through it again...
Whilst our new input buffer board is close to Hypex's Design its no longer on the drawing board, its about a week away from being delivered to customers ears. At a reasonable price, gives them choices to experiment with different OP Amps and requested in response from DiyAudio members. Not to mention sounding very, race through my record collection lovely!
There's a whole community here that can help you develop your product further (as they have done already)...
Thought I would give some input, my new buffers will be amongst the first to be received from Nord - Boggit.
Whilst I would like to let you all know how they sound asap I think it will be a while because it looks like from what I have read that the Bursons require some burn in.
It seems I have two options play music night and day which the wife will love or put them in the oven. Does anyone know what gas mark to use.
Seriously though it seems that comments regarding the Sparkos came without burn in so would they also improve with time or do they sound good straight out of the box.
Whilst I would like to let you all know how they sound asap I think it will be a while because it looks like from what I have read that the Bursons require some burn in.
It seems I have two options play music night and day which the wife will love or put them in the oven. Does anyone know what gas mark to use.
Seriously though it seems that comments regarding the Sparkos came without burn in so would they also improve with time or do they sound good straight out of the box.
Well so much valuable information was discussed since I unveiled the first photos of the NC500's to this forum, I'm not going to copy and paste the last 200 pages or so over again. Best to just take the time and read what's been written if the goal is to learn.
ok I think I finally found the answer. Sorting through all the dribble takes a very long time.
BTW, you did not post a corrected noise measurement of the stock NC500 buffer that I could see. Only one with modifications done.
I also find it interesting that you can hear a difference in noise floor between -126dB and -140dB.
Have you conducted linearity tests of your input buffer versus stock? (That is, distortion while driving a load.) These would be most informative. Given you have access to AP measurement gear it would be great to see such results.
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Well I for one am intrigued about the differences between input buffer configurations. I'd like to hear more user listening experiences and see more measurements.
And I don't think it would be difficult to implement various designs, including Class A. But...I'm not an OEM and so don't have access to the amp modules nor the exact layout required for a custom input buffer module to interface with the NC500 amp module...
You've got it - I tried removing the first VR without sacrificing it first, heating from both sides. It seemed like no amount of heat was enough and I was worried about damaging surrounding components.
For the second VR I cut the pins and all went well, but the damage was already done...
I did read up as much as possible and practiced on some old junk boards, but sod's law and nerves guarantee you'll only make a mistake (or series of bad decisions) when it matters!
Anyway, I have a new stock input board arriving shortly from the gentleman at IQ, and I hope that the amp will come back to full reliability.
No I don't have a comprehensive datasheet for the input buffer. That's to be left up for the OEM's to provide with their finished products. I just had some quick testing done, and the first test it must have been picking up noise. The next test the noise was muted so would better represent the stock board.
And your right, there's no audible noise from the stock boards. Ears up to sensitive tweeters and you hear nothing. The subjective differences in sound are due to the opamps themselves. Anyways I'm done with the stock boards, that was just experimenting I did a few months back.
You can't isolate the op amp from the circuit and say it's due to the op amps. That op amp in that configuration, maybe.
But how do you propose these differences manifest themselves in the sound output? I would suggest the very first thing to check having done a (proper) noise analysis is to examine the linearity of the output versus input for a given load. Surely you have already done this for your own circuit typology given you went to the trouble to examine noise.
Ti33er had previously mentioned the OPA2134. It is interesting to compare the distortion analysis of this op amp in shunt feedback mode versus series feedback mode with various loads. Self provides such analysis in Small Signal Audio Design. The distortion profiles are very different. Perhaps one of these is perceived as better sounding than the others...
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