Originally Posted by adnc
I ordered a board and build pupDAC with the parts I had. I'm impressed how good the sound quality is. There is a slight distortion I think I hear when no audio is on the board. on headphone aswell as on chinch. Also this is not hearable everytime. Does anyone else know this problem? Voltage measurements are all fine.
I'm running it on a raspberry pi and the above problem also occurse on my notebook.
I use pupdac to output my mpd music, but I'm only able to use software driven volume. What about hardware volume controll with pupdac is this possible?
The pupDAC is not really designed to directly feed headphones. If the headphones or earbuds are very efficient, then you may get pretty good results.
The sound that you're hearing could be one of two or three things: 1) clipping while trying to power headphones, 2) the raspberry pi, or a grounding issue on the PCB. I have seen a few threads and comments that indicate perhaps the raspberry pi is not quite up to streaming high-quality audio. Further, the pupDAC has more than a trivial current drain relative to USB from a laptop. (Maybe the raspberry pi has even less power capability, but I dont' know.) A few posts back in this thread, I recommended a powered-USB hub unless you are feeding it from a full size desktop that can handle multiple USB power feeds. As for the ground, this can cause some really irritating and intermittent noise issues. It's one of the reasons that all Beezar DACs use dual ground wires/connections on the output connections.* Without an excellent solder joint, t's very easy to get a poor connection on only one single ground wire with the size of PCB pads that are involved.
Lastly, hardware volume control is sort of self-evident: there is no stereo volume pot on the pupDAC PCB. The pupDAC would be about twice as big if a quality stereo volume pot was included - that was not in the design criteria. However, there's nothing to stop you from wiring a pot externally to the pupDAC outputs. I think an amp would be better, though.
* If you're connecting into the 3.5mm stereo output jack, it only has one pin connected to ground. Try to make certain that the ground connection has a good solder joint.
Edited by tomb - 9/30/13 at 6:27pm