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A "cylindrical object" attached to a USB cable. What is this?

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Found this on Phile-Web, thought it may prove interesting. The Ferrite cores need to be carefully selected to trim noise but not introduce smear in the signal. 


[Series] Gadget TIPS

A "cylindrical object" attached to a USB cable. What is this?

Maritime Shinobi
August 25, 2020
Ever wondered what a tubular object you sometimes see near the plug of a USB cable? It is a "ferrite core", a magnetic material whose main component is iron oxide, which is attached as a measure against noise, and is simply an electromagnet.

Even so, I wonder why some people think that the cables for connecting peripherals to computers and smartphones have noise countermeasures... The reason is "common mode noise".
"DH-AB2F20BK" of ELECOM. The manufacturer explains that it is suitable for connecting to a recording HDD

Common mode noise is a noise component of the same phase on two signal lines, and is differentially transmitted through a USB cable (using two signal lines to transmit signals that are 180 degrees out of phase with each other) It also occurs with cables that do. The generated noise flows through the two conductors in the USB cable in the same direction, and when it travels back through the metal chassis, floor, etc., the cable acts as a loop antenna and generates large electromagnetic noise.

The ferrite core attached to the cable plays a role in suppressing the common mode noise. If common mode noise is radiated, it may affect the operation of surrounding equipment, especially equipment that handles radio waves. However, if a ferrite core is attached, the magnetic flux will be in the same direction, so noise can be reduced.

The ferrite core absorbs the electromagnetic noise generated by the cable as energy. Especially when using devices with built-in radio wave receivers, specifically devices with TV or radio tuners or communication devices such as mobile phones, it is expected to suppress the emission of electromagnetic noise.

If a ferrite core is attached to the USB cable attached to the product, there is a possibility that it will have such specifications after considering the influence on the surroundings, even if there is an aspect of EMC standard measures, so it is easy to use the ferrite core. It should not be replaced with a USB cable without core.

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Most of the USB cables I use for DACs have ferrite cores. Pretty much only exception are the blue USB3 cables I use for Holo Audio devices (and sometimes for iFi too). Since these have different type of cable and connectors.


Typically also noise sensitive devices come with such cables. Like for example scanners, digital cameras and video digitizers. Also quite a lot of pro audio equipment comes with such.


Signalyst - Developer of HQPlayer

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21 minutes ago, Abtr said:

Do you put those on yourself? If so, where did you get them? Thanks.

Yes, they just clip on. Search Amazon for "ferrite rings", lots of options. I bought a package with assorted sizes and one 13mm package for larger power cords.

“The best sounding audio product is the one that exhibits the least audible flaws.”

 Dr. Floyd Toole

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