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Can I filter noise from power supply?

I have 5VDC wall wort power supply, which is a switching supply, and it has a typical barrel connector. But I rigged up a small one-inch square pc board with a USB socket and a barrel socket mounted on it. So, I can use the power supply as a USB power source for charging my MP3 player and other things.

But, when I used this power supply to play music, rather than just charge the player, it was clear there's a good bit of noise in the supply which doesn't show up when batteries are used.

I can't regulate the supply because I need the full 5V, but I wondered if I can add things to the little circuit board that would reduce the noise - such as a series inductor, or a large capacitor to ground, or both. Will those things work, or do they screw things up?

Pics of this setup are here:

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By the way, for future reference, a dumb USB power supply should have its data pins shorted together.

Reply to
Peabody
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What you say may work, it would help to know more about the noise but that's a little more advanced.

Tom

Reply to
Tom Biasi

Was the equipent the mp3 player was connected to grounded / earthed ? That'll be the problem. Most low power SMPS wall warts have a Y capacitor between primary and secondary sides that gives rises to a leakage current at mains frequency and harmonics thereof. That current will run to ground along your audio cable and add a nice buzz ( worse still if the audio equipment has poor / old fashioned attention to internal grounding ).

Graham

Reply to
Eeyore

Filtering is the power supply's job. Why do you want to build what should already exist in the supply? Simpler and probably just as much are power supplies from electronic supply houses such as newark.com, mouser.com, digikey.com, jamesco.com, alliedelec.com, etc. Either buy a 5 volt wall wart that says the filtering already exists, or buy the inductors and capacitors from the same sources to construct a filter.

Anyone with minimal electrical knowledge can build this filter. Simply create a chain of capacitors between the plus and minus wires; with coils (inductors) between each shunt capacitor. Inductors are in series. Capacitors connect in parallel. Every "parallel capacitor and series inductor" chained together means even better noise immunity.

Need more information? Any basic power supply primer will show this filter.

Reply to
westom

You can add more as required for the task. Dead easy.

Graham

Reply to
Eeyore

Try another wall-wart (even if it's an old analog type). They're cheap, widely available, and your immediate friends and family probably have dozens in the garage for things that broke years ago.

Pickup or ground loop problems can account for this behavior, too; can you hear a difference with the ground disconnected at the wall-wart, or with the plug reversed in the socket? Can you find a USB cable with those ferrite-bead clamp filters on it, and see if that helps?

Reply to
whit3rd

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