Originally Posted by jamato8
I do not see how adding the optical in would increase size very much at all. I did this for my Monica II, which was not designed for an optical in but kept all within the constraints of an altoid tin. The current use is very little and it works fine. The optical in requires very little space but you have to have a dac that can use optical.
To fit an optical connector, a switch to select the digital input, and components for a SPDIF receiver, the length of the Pico would have to be increased by about 20%. But what's more significant is the DAC circuit in the Pico uses about 100mA of current, and the headphone amp 25mA, if all of this ran off the battery w/ the optical input it would only last 4.4 hours! There are low power DAC chips out there, like what is found in MP3 players, those would give a good battery life but I am trying to do something special here and sound quality is most important...otherwise why bother? To keep the 20 hour play time using optical the battery would need to be physically 4 times larger. It would also be difficult to add an optical input and preserve the USB performance, the Pico is unique because it does not convert USB to SPDIF and then to I2S as most if not all multiple-input DACs do. It goes straight to I2S there is no SPDIF conversion