[GrandNagus50]

I actually now have two usb dongle DACs, an older Audioengine D3 and also a Dragonfly Red, which I got for use with my iphone (the D3 requires too much power for the phone). I can and do use either of them with my laptop. I have a Cavalli Liquid Carbon amp and I do not have a "regular sized" DAC matched with it, so I just use either dongle as the DAC. It seems to work, but I wonder about the volume level settings. The dongles include both DAC and amp circuitry, so what about the amp part? Where do I optimally set the volume for the DAC? Does it matter? I have read that I should set the DAC at full volume. True, or not? ? I wonder if there is some acoustic scientific basis for dealing with this admittedly small issue, or is it just trial and error?

Doug Greenberg, Berkeley, CA

 

[ClieOS]

Ideally, you should set the volume so that the output voltage at the dongle's amp stage has a gain of 1:1 (*which means the amp stage acts like a buffer for the DAC stage) when you double amp (*while also make sure this voltage won't cause clipping on the input stage of the second amp). That way the dongle will probably be outputting the signal at its best SNR and therefore the second amp will have the cleanest input to begin with. However, (1) determining whether the dongle's amp stage gain is at 1:1 is not easy for most people and (2) most competent DAC makers do tend to design their dongle amp stage to reach / closest to 1:1 gain at very high volume (often around 90% or max volume), so the 'common' recommendation for double amping tends to suggest the user to set their dongle volume to very high or max setting. However, this is not an universal rule and sometime you will find degraded SQ when you set the volume that high. The best way for average user to determine what volume to use is to do a loop-in measurement using software like RMAA over different volume setting till you find the one that gives you the best SNR.