@jaybe thanks for the mention.
This question has been discussed in a number of prior threads, of course. My perception has been that among those who have reported directly performing preamp/no preamp comparisons a significant (but not overwhelming) majority prefer having a preamp in the chain.
I would expect the reasons for that to vary among many possible factors. I don’t doubt that in many cases the reason for preferring a preamp is what George referred to, namely that colorations and inaccuracies in the preamp are subjectively pleasing, and/or are complementary to those of the source component, and/or mask colorations of the source component. But I would expect other factors to be at play in many cases, depending on the specific equipment. Such as better sonics from the source component when its volume control is set at max than when it is attenuating the signal; differences in ground loop effects (which can affect low level high frequency noise and consequently “background blackness,” in addition to potentially causing hum), differences in impedance relationships; differences in sensitivity to cable effects, especially if a long run to the power amp(s) is necessary; and perhaps in some cases what Paul McGowan of PS Audio stated a few years ago in one of his blog posts:
My adamant stance against inserting a preamp between a high quality DAC like DirectStream and the power amplifier should be no surprise to readers of this blog. As well, my subsequent turn around embracing the exact opposite should lift no eyebrows either. But why would inserting an extra piece of gear in the signal path sound better than a more direct approach? How could this make sense?
... For a long time I found that DACs with no-loss digital volume controls sounded better, cleaner, livelier, directly into the power amplifier. Whenever I inserted a preamplifier it sounded different–but not better. That is until I tried a different preamp. My first revelation happened with the stunning Aesthetix Calypso preamplifier. Placed between the DAC and power amplifier, music took on a life and dimensionality that took all of 10 seconds to find it was better–not just different.
... I had written earlier that it’s likely I am asking the wrong question. How could adding more to the signal path make the system sound better, not worse? It turns out the logic is correct: it cannot. So why does sometimes adding a preamp between a DAC and power amp help the system sound better?
Because it’s helping the DAC not sound worse. And that bit of logic is key to answering the question....
... Imagine we have a DAC with an identical output circuit to that of a preamplifier. How would this respond driving a power amplifier directly? Theoretically as well as a preamp and, perhaps, better because we haven’t another component in the mix. But here’s something you may not have thought about.
DACs are significantly more sensitive to power supply changes and noises than preamps. When an output stage struggles to drive a complex load, it is the power supply feeding its output stage that sees these changes. If this occurs in a preamp, it has little effect. But that same situation, when applied to a DAC, has very different results indeed. Small changes in power supplies have big impacts on sound quality–especially jitter.
So this is one reason, and there are more, some preamps can help a DAC.
Generally speaking, IMO the burden of proof should always be on adding anything to the signal path that is not an obvious necessity. But while adding a preamp in the kind of situation the OP describes is not an obvious necessity, due to the variety of factors that may be involved the only way to know for sure in a specific system is to try it both ways.
Regards,
--Al
