USB wall outlets a source of noise in AC lines?

I've got a couple of these on the same mains circuit as my audio gear. I'm wondering if they generate any noise on the lines, since I guess they're just small switch-mode power supplies. If so, would they make the noise all the time, or only when something is plugged in?

Can't say as I'm hearing any noise or sound quality impact, but would appreciate any suggestions or thoughts.
4197d8ef 0ecf 47d9 9002 6a5320603594john_g
I can hear when dimmer switched lights are on. I have dedicated mains runs from the breakers. If you can, try reduce all pollution. I’d get rid if them.
A dedicated line just to my system would be great, but isn’t practical in this dwelling without tearing up a bunch of drywall. Fortunately the house was built in 2005 and has a 20-amp, 12 AWG dedicated circuit just for outlets in the listening room, and I can ensure that nothing else is plugged into them. And just yesterday I made sure that circuit was fed from the top breaker in the panel, which is supposed to have benefits as well.

So I just removed the USB outlets and things sound good, possibly better. Took one of them apart and found it contains, as you might expect, several capacitors, a small transformer, and a couple of PC boards. So far as I can tell the internal workings are not "switched on" by insertion of a USB plug. I'd post pictures but I don't know how to do it on this board.

So, who knows? A cheap tweak, anyway.
Hi John, the question is whether you can hear it. :)

Furman with LiFT and SMP provide some of the most cost effective line noise reduction, especially on sale. :)


A dedicated line is not needed and does not solve RF problems, esp. when you realize that most noise problems are caused by grounding issues and/or are generated by your components, not outside the line run.

Get rid of all fluorescent lights, and move the USB outlets and LEDs as faraway as possible.  Make sure you have everything properly grounded, and get move your router away from the HiFi.

For a DAC, consider that it may want a low inductance cable run from the wall wart (not all do); you can DIY for ten bucks.

An isolation transformer is the size of an amp and can be had on eBay or elsewhere (I think they are being sold off my hospitals).  You might need an electrician to wire it in.  I would not bother unless I was sure I needed one...

Current thinking among (some) digital engineers is that noise is not just altering the DR of your music but is causing jitter.  I will bet we see some improved DAC designs in the future.