Ivan TT
500+ Head-Fier
In defence of OPA1622 on a circuit board (cheap ebay version), it works just fine in practice, even if in theory there are some valid concerns about using it on DIP8 PCB.
Ground is derived from splitting rails using resistors indeed, but it does not manifest in increased DC offset (I observe sub-1mV DC offsets in my fully DC-coupled setups), and John mentioned something like 3-6dB noise increase in noise above 10kHz if using this arrangement, which is negligible (and probably would still be below many opamp's noise anyway).
Ebay board houses 2 power bypass caps (not sure if John's had those), which helps.
I ususally replace resistors with extra set of caps (actually, I replace resistors and stock caps using 0805 0.1 and 22uF caps) and then provide connection to ground via extra wire, if using OPA1622 as a permanent solution. I also customary configure them as voltage followers, as they work as buffers just fine (and it requires only 2 bridges on DIP8 PCB board).
But also OPA1622 is perfect for driving HP directly, as it has high capacitive load ability, high current output, short protection and lowish output impedance, so even on a PCB board it is perfect replacement for any DIP8 socketed opamp driving headphones well worth consideration.
Downsides of OPA1622 that I noticed: low-level pop when powering up (even when using delayed power on using enable pin), it is also quite susceptible to EMI.
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if you actually need reasonable amounts of current but not too high the NJM/JRC4556 is perfectly acceptable but it isn't my first choice in situations where some kind of buffer helps with performance but you don't need lots of current.
