IV stages are a bit of a different case, here I would champion the use of a very fast current feedback opamp designed for video mostly, as the glitch energy of delta sigma type dacs in particular is at very high speed, but you cant just drop current FB chips in place of voltage FB.
I'll try some video op-amps soon, after XX hours of listening the LT1028, OPA827 and MUSES are the current favorites in my DAC I/V stage. It's difficult to know which one is the most revealing, and if I was blind evaluating the MUSES I suspect I'd completely overlook it.
I think you are misunderstanding the term line out. line out simply means line level voltage output, just a reference level voltage so that engineers know they arent going to blow or clip the input of their amps or mixers as they know what to expect. it has nothing to do with whether there is a circuit in the output and an IV convertor is simply there to give that standard level from a current output. this could be a simple resistor, a discrete jfet IV, or transformers along with many other types.
the above quoted specs I wouldnt take anything from the above, the 3 dacs have just taken the ideal datasheet performance from the dac chip, nothing to do with its performance in the application.
the below is a table for the line level single ended standard. in reality dacs are all over the place, the sabres balanced out for instance is about 3vrms @ 3.9ma which is about double the +6db SE standard, so pretty hot voltage, but lower than normal current.
Some current out dacs will handle passive resistive IV well, depending on their voltage compliance and current, others will not handle it well at all, with the sabre the THD+N is not great with passive IV, but some still prefer the sound. I personally dont like passive IV all that much; its a bit musical for my taste, top end lacking sparkle, easy to listen to, but for me dynamics are compromised, at least with the dacs i've tried it with.
|Use||Nominal level||Nominal level, VRMS||Peak Amplitude, VPK|
|ARD, Germany||+6 dBu||1.550 (approximate)||2.192 (approximate)|
|USA professional audio||+4 dBu||1.228 (approximate)||1.737 (approximate)|
|Consumer audio||−10 dBV||0.316||0.447|
the voltage out dacs, like the one you mention and wolfstons, should be buffered, not connected directly, they should not be loaded with capacitive cables etc and usually have an internal opamp anyway. so if you just have a well designed transparent IV stage that you leave constant during the tests, then this is just as valid as a baseline.
I generally prefer current out dacs as I like maintaining control of the IV stage, but i'm quite intrigued by the AK4399, so have picked up a couple of chips and a suitable proto board
I don't think the PCM5102 has an internal op-amp like the ES9023, or it wouldn't be called voltage-out, or am I missing something?
While your repy was helpful, thanks, my wave of thought is on a purist perspective. For example in my Teclast T51 the 'line-out' has OPA2604, I don't want that horrible chip there colouring the sound in my experiments, I need a 'pure' line-out, even if only in theory. As you can see in my JVC FX500 modification I like removing filters from the signal, digital and acoustic.
In short I'm considering the Musiland Dragon, TeraDak 2.6 and Colorfly CK4 right now, I just don't have the technical experience to know if these are the right choices for my 'line-out' experiments and listening!
The toasted OPA627 was in my DAC. The 9V batteries in 2x, 4x, 6x are connected to a DIY portable amplifier.