Im interested in op amp rolling for my amp since its not expensive to try out and I was surprised to find a lot of variation between them, the amp has a very simple circuit so my results could be more siginificant than with other amps. Using hd600s and 400is to test them Ive compared the NE5532, NJM4556 and LM4562 so far. LM is the best overall, it sounds the most balanced, very natural/smooth/clean, doesnt exaggerate anything but can sound lacking in impact. strangely its probably the most boring sounding one when paired with 400i but the best sounding with hd600 NJM has a more analytical, detailed sound but it sounds a bit thin and isnt as smooth... This is also used in o2 amp and it sounds like this op amp defines the analytical sound of that amp, I will have to try the LM in the o2. NE was the most coloured sounding, seemed to hide a lot of details but had a fairly musical, mid-focused sound, could sound uncontrolled in very intense tracks... however there was loud pops and click when powering on and off the amp with the particular IC I had, seemed to work ok otherwise but I ordered a replacement to be sure I heard its real sound. I am curious to see if there is more room to improve with other op amps? So far I read the OPA2134 as an upgrade to the LM but its quite expensive, has anyone experience with this op amp or do you know any op amps that you consider an upgrade from the LM4562?