Stefan Brüns wrote:
On Samstag, 23. Januar 2021 18:52:50 CET Per Jessen
Per Jessen wrote:
I have hooked up a headset to my Nanopi Neo Air,
but the microphone
quality is severely impacted by electrical hum. I have tested it
and determined it is due to a power supply with no ground, i.e. the
typical 5VDC 2A with a two-prong Europlug. Using one of those
small power supplies in metal cabinets, with a ground wire, and the
hum is gone.
The latter is not really an option, so what do people do instead?
I have discussed it on EE stackexchange, and there is no doubt it is
a ground loop (Brummschleife) issue
There is no doubt this explanation is utterly wrong. You can't have a
ground loop without (multiple!) ground connections.
I don't even have a single one :-)
* connect an oscilloscope ground to the ARM board, the hum goes away.
* touch the metal part of the microphone with my finger, the hum roughly
* use a small 5vdc SMPS with mains ground, no hum.
There are other possible explanations:
- badly shielded cables
I have tried using a shielded balanced pair cable to the microphone, but
the microphone capsule is sat in an old analog telephone receiver with
an unshielded spiral cable anyway ...
- conducted noise from some other part of the
equipment, e.g. monitor,
external amplifiers (AV Receiver), ...
No monitors, no amplifiers - only the ARM board, the microphone, the
wifi aerial and the powersupply.
- bad (unsufficient) power supply
I have tried four different ones - Goobay 2A, another one bought
specifically for a Raspi (2.1A), a large Ikea multi-charger 3400mA and
even an Iqos charger. Same problem with all of them. Use one with
ground, and the problem disappears.
You should try disconnecting all external equipment
save the headset
and then verify the noise persists.
That is what I have :-) I record a sample with 'arecord', then copy it
to another box to listen to it.
Per Jessen, Zürich (2.6°C)