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.

Andy Burns wrote:

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.

I had to try ...

I can see the chromecast spitting red light down the fibre (which it
turns on/off when it's streaming/silent) the DAC is powered by USB, but
only silence comes out of its phono outputs, seems I had mis-remembered
that the DAC has S/PDIF output rather than input :-(

Anyway, it proved that it would be *way* too much spaghetti, even if it
had worked ...

On Monday, 6 January 2020 14:49:48 UTC, Andy Burns wrote:

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?

USB negative power is usually connected to the cable shield.

You could isolate the USB power with something like this:
Farnell: 2747515
REC5A-0505SW/H2 Isolated Board Mount DC/DC Converter, Medical, 1 Output, 5 W, 5 V, 1 A
It is almost certainly overkill and you can probably find something
similar for a lower price.
John

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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"Andy Burns" wrote in message
...
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.

Brian Gaff wrote:

I ended up with a
several way usb with power supply

I tried a good 60 watt USB charger (1x USB type C, 4x USB type A and 1x
USB quickcharge port) it was as bad as the cheapy two port 2A charger.

Was trying to avoid clutter ... have decided on a method that has more
clutter, but it is hidden!

wrote:

USB negative power is usually connected to the cable shield.

You could isolate the USB power with something like this:
Farnell: 2747515

I think I'll just move the speaker to the other side of the room, where
a 4-way mains power strip and multiple USB chargers can be hidden on top
of some cupboards ...

Pamela wrote:

If you get interference with a splitter then wouldn't one (or both) of
Chromecast and speaker be failing to pass on the true ground potential
from the USB input internally to their respective audio connection?

As opposed to the Chromcast injecting spurious interference back through the
USB power input.

Well, the interference only happens when speaker and chromecast are
sharing a USB power source (cheapy 2x output charger, more expensive 5x
output charger, or single output charger with splitter cable)

If one is on battery, or they're both on individual chargers, it's fine.