The reason I kept
NOS DACs out of it is that many NOS DACs measure horribly - I would expect this to result in oft-audible differences. ....<snip> I'm not a NOS fan
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Regarding DAC chips, they can be implemented in different ways - the aformentioned NOS approach, for example. However, the overwhelming majority of DACs are implemented in a way that does much the same thing as other DACs. I might have multiple chips, one per channel, to improve SNR or I can resample to various different frequencies. However, these differences in approach generally result in small differences which are unlikely to be audible - with the exception of the minority approach such as eliminating oversampling.
So I can say the majority of vaguely modern DAC chips, implemented in vaguely conventional ways, sound the same. My original statement was perhaps a little too sweeping, but not by that much.
Opamps is a bit of a horny one for me personally. Tangent's opamp sound signature analysis has several aspects of it which makes it inapplicable to opamps as used in DACs:
1. The cmoy is a design which drives a difficult load (a headphone) directly with an opamp. This means that factors that would normally be dealt with with MOSFET buffers and the like in better amps can affect the opamp itself - for example, many cheap cmoys have uneven frequency responses.
2. Opamps, even in the simplest of circuits, are not neccessarily drag-n-drop. The "opamp rolling" which many people participate in always makes me feel slightly uneasy, because dropping in one opamp which has vaguely similar specs and hoping that the circuit won't mind is not neccessarily a good idea. However, I find it extremely unlikely that Tangent didn't take this into account - indeed, he speaks of oscillation and the like in his article.
3. In the end, it was a sighted test, whilst it is also unclear whether the volumes were matched. Anyone who has done blind testing knows how monstrously obvious differences can suddenly disappear.
However, in the end we are not looking at the measurements of the opamp - we are looking at the measurements of the whole. If the designer has used some weird and wonderful opamp and still managed to turn out a measurably exemplary product, bully for him!
As to your closing points, no-one is suggesting that every DAC and amp under the sun sounds exactly the same. The title of the other thread was more a provocative point to get people posting. However,
there is no reason why a Benchmark should sound different to a DACmagic, nor that to the $6000 dollar dcs Puccini - as they all measure very well. Hell, you could probably go considerably cheaper than the DACmagic. If your point was that not every conceivable DAC and amp will sound the same, consider yourself vindicated
Regarding differences as expected/not expected, it's difficult to draw anything from this as to their nature. Perhaps you were subconciously hoping for this cheaper DAC to turn out better than it's peers. Alternatively, there were real differences that would also be easily measurable as significant - it seems unlikely, but not having the measurements of any of those products in hand, I cannot instantly dismiss it. However, were there significant differences in the measurements from what was expected (0.5% THD for example) then I could safely say that rather than one of the DACs being special, the others were merely inferior to what you would expect. Again, it's difficult to draw any conclusions from your specific example.