Amir says in the review for the Audiophonics HPA-S400ET/Purifi 'If you have a pro interface that goes up to 10 volts out, you can utilize the low gain mode'.
What's the point of DACs having higher voltages then? If it's not to make amps sound better what is it for or to put it another way is there any case in which it would be beneficial to have a higher voltage?
The point of DACs having higher voltages is twofold:
- To make a preamplifier irrelevant and to allow full/loud playback volume with power amps that don't provide the 27-29dB of gain that a lot of traditional Class A/B stereo amps provide (or the 29dB of gain that's the THX standard for home theater and such). Even at high gain, most Class D amps, including the Audiophonics unit, provide abut 25-26dB of gain. And at medium/factory-default gain, the Audiophonics provides about 20dB of gain (as do many other Class D amps). This lower gain translates into small differences in max perceived playback volume, but they are differences nonetheless.
- To take advantage of the lower noise floor of the DAC compared to most amps, especially when the DAC is outputting at high voltage, as the noise tends to stay relatively constant, which means that the noise floor of the DAC goes down relative to the voltage of the signal it's outputting goes up. But the Audiophonics amp, as tested by Amir, has extremely low noise of its own, and in some respects it even beats the Purifi EVAL board, which some folks here have suggested means that the Audiophonics buffer and/or circuit layout are implemened in a very clean, low noise manner.
So putting those two points together, there is certainly nothing wrong with maximizing the output of the DAC and running the Audiophonics in low-gain mode, where it provides only about 12-13dB of gain. But this amp is so good that you don't
need to restrict yourself to DACs that can output 10V. Also keep in mind that for reasons of standardization and consistency, Amir generally tests devices (like DACs) at 4V output. A well-designed DAC capable of outputting 10V will probably have equal or better noise performance at 10V than 4V, but this is not certain. Some devices - for example the MiniDSP SHD - actually clip if their output is set to full gain (I believe the SHD clips at -6.5, which for that unit is over 4V but not much over), Others are more knowledgeable than I am about how various DACs achieve up to 10V output, but if they are doing so by adding extra amplification, then they are basically preamps, and in that case there's no guarantee that their extra amplification performs better than the input buffer in the Audiophonics amp.
Any DAC that has excellent measured performance and balanced outputs (enabling 4V output) can pair with the Audiophonics amp set to medium/default gain, and the sonic result will have a noise floor totally indistinguishable (by human hearing) from a 10V DAC output paired with the Audiophonics in low-gain mode. So that opens up your DAC options, enabling you to consider options that might cost less, or have different/better usability, and so on. But of course the RME units are always an excellent choice - they're just not always necessarily the most economical choice,