[Voyage-linux] Cubieboard 2 and MPD, (and NO external DAC)

[superpat]

Hi,

As promised I tried 'scoping my Cubieboard 2 running MPD today. This is the
frst time I have tried to 'scope a SOC board.

No matter how and where I grounded my 'scope probes, I was unable to measure
the noise on the analogue output stereo connector, because the whole area of
the Cubieboard was swamped with bursts of HF switching noise, generated by
the Cubieboard itself.  The noise was present when the Cubieboard was
running, but the MPD app was not started.

I even tried floating the 'scope and using two probes in differential mode,
one to the ground plane, the other to audio signal, but I was still swamped
by the HF clock noise of the A20, I think being picked up in the high
impedance 'scope leads.

I have NO idea how to achieve meaning full measurements of the noise floor
for the ADC and audio output stages!

All I can say it is a bl**dy wonder that MPD works as well as it does in
that sea of noise, Power supply noise is minor compared with the SOC
electrical noise.

I will try to find the proper method of 'scoping SOC  boards, the literature
must be out there somewhere.

cheers

Patrick



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