Hum problem in DAC - weird behavior - need help

[ENSen]

Interesting, I do not remember how I connected the ground (I built it four years ago). I have to check.

Many thanks

 

[ENSen]

Ahh, yes.

And indeed it was a grounding issue.
I forgot about the Vref ground of the SEN. With a buffalo DAC Vref should be Vavcc/2. The ground reference for Vref is best taken from the Buffalo Vavcc main ground right after the smoothing capacitors (at the PlacidHD or whatever someone is using). NOT from the local ground next to the Vavcc output at the buffalo. Rooting a wire to the main ground creates a larger loop are (or wire length) of the hookup wire, but this does not matter. It took me a while to figure this out, but with this little change I have a completely noise- and hum-free setup.

This solved my hum problem as well! Now I can also use the SEN single ended output without problems. Many thanks.