Filter USB power?

I have a set of LTB headphones. These headphones are designed for use with a PC. They have an amplifier that is powered from the USB cable. Unfortunately for me, my DFI mainboard seems to have really dirty power on the USB ports, which causes buzzing and clicking. A fair number of folks have this problem with the headphones and the official fix is to "use a powered USB hub" instead of connecting directly to the PC's USB port.

I'm hoping that I can clean the power up by simply adding a couple capacitors to the amplifier (or even USB ports on the mainboard).

Since this isn't noise at any specific frequency, I'm not sure how I can choose the most effective values for the capacitors.

I'm also wondering if a ferrite ring would help here?

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Normally, the USB power lines already have inline ferrites and bypass capaitors that are designed to filter the power lines. The USB specification calls out for allowable voltage drops, transients, etc but perhaps it allows more than your application can tollerate.

I am a little confused, though. You make it sound like the headphones are receiving power from the USB, but that they don't get the data from the USB port. If this is the case, this may be part of the problem. If the data is coming from the USB port, it would be digitally transmitted and this should go along way towards prevent noise contamination.

You may be able to place a small valued capacitor across the +5 and GND lines from the USB port. This would shunt AC components to ground. It is hard to say what a good value would be as it depends on the rest of the circuit that is hooked up and its input impedance. I would suggest that you can experiment, trying different values ranging from 47uF to .01uF and see what happens.

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I guess they try to save money wherever they can. I've got the USB cable wrapped around a ferrite ring a few times and most of the noise is now gone.

That's correct. They just take the analogue audio from the soundcard and pull power from the USB port to power the amplifier.

True... I considering going that way, but I wanted the headphones to be portable - no drivers needed.

The ferrite ring seems to have done the trick. If I notice any change I'll pop the amp open and add some low value caps.

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