I think that what one gains by using an active preamp is dynamic headroom and the potential for "better" loading. Much of this can be negated and bypassed if the output of the DAC or CD player is rated for the same appr voltage that a preamp would produce i.e. way above 2 volts AND the impedances between the DAC and input of the amp are taken into account.
Even though most amps would be roaring with 2 volts fed into them from a normal line level output on a steady state basis, that does not mean that the simultaneous peaks that may last microseconds would be reproduced at full amplitude. That is, if the output of the one box player or dac is limited to 2 volts as a max output level. In other words, the dynamic status of music "may" require higher output than what a standard line level output may be able to provide on a short term basis. Adding an additional gain stage between the DAC and amp and the associated headroom that comes with further amplification ( the active preamp ) may be why things sound more dynamic. The fact that this also alters the impedance that the source sees and adds a "buffer" in terms of the signal that is modulated back to the source from the amp may also come into play. I say this as i've read more than a few statements to the effect of things sounding "cleaner", "more focused", "more resolving", "increased body and weight" etc.. with a preamp hooked up.
Keep in mind that all of this is just an educated guess. I arrived at these conclusions from playing around with a DAC that can provide 4.5 volts rms. This DAC has standard line outs to feed a preamp along with another set of outputs that are fed from a stepped attenuator for direct feed to an amp. I could hear no difference in performance when switching from "direct drive" with the DAC & built in stepped attenuators feeding directly into the amp and when i went to the dac using the outputs that bypassed the stepped attenuators into the preamp and amp. This tells me that the dac had no problems driving the amp and there were no problems with loading. It also tells me that the preamp is extremely faithful to the source and did not contribute or detract from what it was being fed. Both situations made me happy to say the least. I kept the preamp hooked up as the added versatility of multiple inputs was a necessity for me in that system. Sean
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