A very compact USB sound card with either two line inputs or two line outputs
- USB-C connector (USB 1.1 standard)
- Can be set to Line Out or Line In with solder jumpers
- The front plate can be flipped for Input or Output labeling
- Bus powered
- With PCB front plates no mechanical work is neccessary (except for some countersinking)
The main chip of the audio interface is a PCM2904 from Texas Instruments. It has an in- and output capability of 16bit at 48kHz, enough for most applications. A high-quality OPA2523 op amp is used as a low-pass filter to get rid of high frequency noise. It's basically a copy of the PCM2902 eval board from TI.
On the underside, there are six SMT solder jumpers. Four of them determine the direction of the input/output LPF, so configuring the device as a Line In or a Line out device. In case of a Line out configuration, the two inputs can be tied to GND to avoid any noise.
The PCB and the front plates are designed to fit inside ultra small Hammond 1455D601 metal case. But if you want to save ~15€, you can download the 3D CAD files for the case and print it for yourself: https://www.hammfg.com/part/1455D601
Although a nice anodized aluminum case is pretty nifty!
It would be really nice to be able to change the direction mid-operation, but that would require some analog switches. Maybe I'll create another version somewhere in the future