[Duncan]

Simple question I hope, my cursory look around Google didn’t give me answers to shout about…

I have a battery powered amp, and if I charge it through a mains charger (whether single or multi port, branded or not, and with or without a mains filter) I get an annoying (what I assume to be ground) hum - but if I charge it through a cheap Anker battery pack, no such noise.

I can’t believe it is dirty mains supply, I did think it was something poorly designed in the amp charging section, but I’ve killed that idea with it being quiet being charged by battery.

thanks.

 

[71 dB]

What happens, if you detach the amp from all sound sources while charging with mains charger (i.e. only the charger and headphones connected) ?

If the hum goes away it is about a ground loop.
If the hum remains it must be badly filtered AC ripple from the charger.

 

[bigshot]

Odds are, it's a grounding issue.

 

[Duncan]

I’ve switched from an unshielded cable to shielded, and plugged in or not, using an (actually multiple) AC USB charger(s), the noise remains, but not on a battery powered charger, odd!

 

[bigshot]

Ground loops are hard to track down. Take a grounded wire and touch it to the chassis of your amp and see if it goes away.

 

[71 dB]

Shielding doesn't protect against ground loops. It protects against interferences.