riverlethe, I know the feeling, trust me.
I usually don't trust people when tell me that changing op-amps will change the sound, but sometimes A/B tests and also scope's measurements tells the contrary.
I've also read nwavguy's entire blog myself for several times (even the comments sections) and I totally understand how O2 works and what a great job nwavguy did. Also, if you look at my previous posts about what I've did to my O2 you'll realize that I did a couple of more improvements in the past, not only op-amp rolling (of course, who looks for real O2 upgrades will need to check AGDR's work from diyaudio forum).
I was only using my PicoScope to check for any possible oscillations and to measure voltage output for several audio signals taken from audiocheck.net (at least 10 wave forms at around -3dB each, between 20-20.000Hz, dummy load resistive & capacitive was used). Output signal is completely flat and no strange FFT harmonics could be seen no matter of the op-amp used (well, with some op-amps I could see an increase in THD but only when output voltage gets close to 7V RMS, but that's another story).
Two things I need to point out here:
- most op-amps have been created for "general use" and only few of them are really created "for audio use"
- V5 is completely solid-state with perfectly matched transistors and 0.5% film resistors and has been created with VAS and LPF stages in mind
- VoltageAmplificationStage and LowPassFilter are the stages where the sound
could and will get changed inside an amplifier; adding I/V stage for a DAC as well. Output buffers might also the influence sound as well, but usually LM4562/LME49720 if
correctly decoupled should be OK for most audiophiles, even in A/B tests, though some people found real differences when rolling output buffers (I'm not the one of them yet).
In O2 sound is created inside the first op-amp, because the output buffer is acting like a blind audio repeater. We all know the limitations of NJM4556, still sound is not changed there, actually the sound could be changed in the voltage amplification stage, so NJM2068 is the op-amp from where the sound actually comes from. So, replacing this one with a real solid-state device like V5-dual from BURSON might be a real upgrade for some of us, especially for mod-ers and DIY-ers.