Yes sometimes you get rubbish on usb supplies. There is no answer other than
use a very good usp powered hub thingy. I had this with a sound box getting
whining and ticking from the computer usb. Just a simple usb psu did no good
as the supply was not isolated, just beefed up a bit. I ended up with a
several way usb with power supply, but the annoying thing for you is it it
is the usb device which is generating the crap, so really that needs to be
the device powered by the main unit and the good isolated hub powering the
audio stuff. Another thing I've noticed is that if I start hearing the start
of a whine again I remove all plugs give a squirt of cleaner on the plug end
then work them in and out and its gone for some more months, leading me to
think that the contacts are not plated or maybe very poorly.
Brian

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The Sofa of Brian Gaff...

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"Andy Burns" wrote in message
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I have a portable speaker, with a rechargeable battery, it takes in power
via a uUSB, it also offers power out via a USB type A.

I can play audio to it over bluetooth, or into a 3.5mm aux socket, the
bluetooth quality isn't the best (no AptX) and neither is the range.

I have a chromecast audio, this also takes in power via a uUSB and has a
3.5mm aux output[*].

If I plug the chromecast aux into the speaker aux, and power it from an
external USB charger, and stream music while the speaker is running on
battery, all is good.

If the speaker is powered from one USB charger, and the chromecast is
powered from another USB charger, all is good.

I've got two 13A sockets nearby the speaker, but need three devices
plugged in.

However if I power the chromecast from the speaker's USB power out, even
when the speaker is running on battery, I get all sorts of horrid
"motorboating" and clicks like on an 1980's international phone call.

If I power both the speaker and the chromecast from a single USB charger
with multiple outlets, or using a uUSB "Y" splitter cable, I get the same
interference.

I presume the chromecast is spitting out interference on its power input,
which the speaker objects to as it's relative to the audio ground?

I looked to see if there's such a thing as a USB isolator, they do seem to
exist, but are north of £50 which seems excessive,
If I pared-down a USB cable, so it only has the power +/- pins, no data
pins and no shield, is that likely to help? or do USB sockets generally
link the -pin to the shroud?



[*] Cunningly the same 3.5mm aux socket is also an S/PDIF optical output,
which I suspect would help with isolation, if I fed it into a DAC (I have
a spare) but then it doesn't help overall because the DAC would require
yet another power source that I don't have a socket for, and would add to
the spaghetti.