USB power supply.

[Dave Plowman (News)]

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.

[Adrian Caspersz]

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).

[Michael Chare]

8 outlets is quite a lot. I have 5 and 6 port ones which are convenient for going on holiday and have figure of 8 mains input sockets which I use with an appropriate cable.

[alan_m]

Are all the outlets the same power rating? If not try one output that can supply a higher current or, if possible, try your Toslink adapter on its own in the 10 output power supply.

Does the total load of your USB devices exceed the total power available from your USB power supply brick? For instance in may be rated for a total of 50W which equates to 10 USB outputs at 1Amp. If you were using all 10 outputs and a couple required, say, 2 Amps, then the other outlets may only be able to supply 0.75 Amps or maybe when reaching overload the regulation of the power starts failing

[Brian Reay]

Depending on the loads, you could be simply over loading it and it can?t regulate properly.

Unless by your ?Happens with only it plugged in? comment you mean you still hear it with, say, just your amplifier and speakers and no USB devices. That suggests a the beast has an inherent noise problem. Price doesn?t always equate to quality in terms of noise performance BTW- plasma TVs were very expensive but very electrically noisy.

What make is it? I find Anker ones are generally pretty good. I don?t know if they do an 8 way one but certainly a 4 way.

[Brian Gaff]

Yes psu noise in analogue circuits is something I find I get on usb powered devices. It seems to be on the earth as well. Some devices are more prone than others. It seems to be a factor of many tings particularly computer usb sockets. Brian

[Brian Gaff]

No that will not happen. In many cases its tings like the behringer audio pc interface that seem most prone. Short of getting inside and adding decoupling, if that were possible, I ended up with a powered usb hum, and found one particular socket was best. Of course then I wired in the TV and found the video cable from the pc made it have what sounded like a 100hz buzz all the time. sulk. Brian

[Dave Plowman (News)]

The device is quite a posh one, and shows on its screen how much current each outlet is taking. But I did say I'd tried it with only the Toslink unit plugged into it with the same result.

[Dave Plowman (News)]

It would be some poor device with a large number of outlets which couldn't supply the maximum USB can handle to only one of them

Not quite sure what you mean. The noise comes from the combination of the Toslink adaptor and that power supply. Even with the optical cable unplugged. Change the PS and the noise goes.

I'll look later.

[Lee]

I'd hazard a guess here, that this device was intended to "charge" things rather than provide "clean" DC for audio stuff...

[Dave Plowman (News)]

Did wonder. Although the description didn't say that.

[Dave Liquorice]

Poor filtering on the output(s) of the new SMPSU and/or poor power rail noise immunity of the adapter. Running te USB power cable through a ferrite coore might be enough. Failing that an inline LC filter, two ferrite cored tordial coils in each leg with a 0.1 uF capacitor across the in and out. Coils need to made from fairly hefty copper wire to avoid significan't volt drop. It does take much R at 1 A to drop the complete tolerance range of USB (5.25 V to 4.75 V).

Pragmatic solution: use that PSU.