On 30/09/2019 15:05, Dave Plowman (News) wrote:
Have a few devices in the AV setup which are USB 5v powered. To try and
keep things as neat as possible, all the mains to that are now IEC, as
that takes up less space than 13 amp.

So decided a USB power supply would be nice. One where the PS was internal
rather than a wall wart, and a main cable I could fit an IEC plug to.
Found one on Ebay with 8 outlets - not cheap either.

One of the things it would power being the a Toslink to phono adaptor -
TV audio into the amp. Which was just fine on its supplied 13 amp wall
wart. With a USB to USB lead.

I now get a noise like a distant burglar alarm on its output with the new
PS. ;-) Changed back to the original PS, OK.

Not a ground loop either. Happens with only it plugged in.


Poor regulation or filtering, and that before any of the same is done in
the device. Maybe there is a ferrite choke you have omitted in your
rewiring?

Do you have a scope so you can look at the power rails?

Or just send it back (which will stop Brian screaming as it is probably
also doing something to his radio as well).

--
Adrian C