Stefan Brüns wrote:
On Samstag, 23. Januar 2021 18:52:50 CET Per Jessen wrote:
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 doubles. * 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)