Design Retrospective

Overall I am pretty satisfied with how this project turned out. The audio quality is superb (at least compared to my previous set up) and the device fits nicely within the channel strip, as opposed to having clunky interface boxes. There are a few things I would want to improve for the next iteration.

First would be to come up with a better overall mechanical design. Depending on the holding force of jacks on the mixer, it can be a little tricky to unplug it from a mixer. I would probably want to figure out some kind of external (3D printed?) case to screw the plugs to. I would also probably add mounting holes to the PCB to offer some additional stability/strain relief.

Second, would be to see if I could squeeze in an external ROM. The PCM2706 does not require an external ROM, however, if you want to use custom USB descriptor strings, you would have to set those up on the ROM. This would be useful for when you have multiple devices connected to the same computer and you wanted each to have a unique name. As it stands right now, I don't have a need for multiple cards on a single computer, so I had left it out of this first iteration.

One question I had from someone in the Hacker Channel has the reasoning behind the selection of the PCM2706 as the DAC for this project. The selection was based upon the goals of this project, keep it small and keep it cheap. The PCM2706, as far as I have been able to tell, if the cheapest single chip solution I could find. The typical USB DAC design pattern these days is a two chip solution, one to go from USB to I2S and another to go from I2S to audio. This ends up being a problem for two reasons: first, two chips is more board area which makes it larger and second, two chips would be more expensive than one. The PCM2706 is an older design (2003 I think), and it is limited to 16-bit/48kHz sample depth/rate, however, for playback that is a non-issue. If I were to do it again, I think I would still use the PCM2706, for reasons of cost and simplicity. If I were to make another design for recording, I would probably go the two chip route for a higher sample rate as there are some advantages for higher sample rates for recording.

Video Demonstration