Originally Posted by fubar3
What about slew rate? There seems to be some hype or emphasis on that factor. The LM49610 can do 2000v/m-sec which is 600 times faster the NJM4556. What difference would it make to a headphone enthusiast?
Slew rates in the range of thousands of Volts per second are mostly a marketing feature for driving dynamic headphones. The slew rate required for a sine wave at frequency 'f' and voltage 'Vp-p' (peak to peak) is ℼ * f * Vp-p V/s. Therefore, the NJM4556 in the O2 allows for a maximum frequency of about 47.7 kHz at its 20 Vp-p output before slew limiting occurs. Of course, in practice the distortion usually starts to rise already before the limit is reached, but for typical CD quality music containing frequencies up to 22050 Hz, the O2 has enough "headroom" as far as slewing is concerned (it is also useful for not perfect reconstruction of the signal by the DAC filters, but modern oversampling DACs with a decent analog filter stage are not too bad in this aspect).
In the case of buffers that are intended to be used in a feedback loop, like the LME49600, the very high speed is useful to minimize the loss of phase margin due to the addition of an extra stage (i.e. the open loop frequency response of the op amp hopefully rolls off to 0 dB before the buffer starts to introduce a significant phase shift).