[LAU] USB cable with ferrite core

[Schatzman, James]

1) Perhaps it is not so much the issue of whether the cable has a ferrite RFI suppressor but the quality of the cable that is important. I recommend that you use a quality USB 2.0 spec'd cable. Better yet, use a USB 3.0 cable.

2) Unfortunately, USB is inherently noisy. Using a ferrite to reduce common-mode currents in the cable is, in principle, a good idea. However, there are potential issues.
 Either or both the sound card and your computer's USB port may not properly isolate the signal and power grounds, and there may then be noise issues if the two grounds are not electrically the same. When you install a common mode choke (the ferrite), you are effectively isolating the two grounds. This should be fine, but if either sound card or USB port are not properly engineered, there could be a problem. You could try running a wire (16 gauge or larger) from the chassis of the sound card to the chassis of the computer. Do not put a ferrite around this ground wire.

3) Another potential issue is the sound card power supply. Unfortunately, almost all power packs sold these days in the U.S. are Chinese switching power supplies which produce TREMENDOUS RFI. You could try a linear power supply instead, although they are getting harder and harder to find.

Jim

________________________________________
From: Linux-audio-user [linux-audio-user-bounces at lists.linuxaudio.org] on behalf of Ralf Mardorf [ralf.mardorf at alice-dsl.net]
Sent: Wednesday, December 28, 2016 3:11 PM
To: LAU
Subject: [LAU] USB cable with ferrite core

Hi,

if I connect an active USB hub and an USB audio card by a 1.5 m USB
cable, there are no xruns. If I connect the devices using a 0.5 m cable
with a ferrite core [1] there's one audible xrun after the other.
Technically a ferrite core affects the quality of a digital
signal, but I wonder if it could be that much, that it could cause
xruns. Maybe just the cable or the jacks are bad. Does anybody know
more about USB cables with ferrite core and possible impact on the USB
signal or other reasons that make a differences for USB cables or USB
jacks?

[1]
https://www.reichelt.de/USB-Kabel/DELOCK-82057/3/index.html?ACTION=3&GROUPID=6099&ARTICLE=144663&OFFSET=16&SID=96WGQzM6wQATIAAC1mEnc6b2149a65e87e5dd30debfec249184e8&LANGUAGE=EN

Btw. the iPad now could connect to the PreSonus and shows all I/Os, but
neither MIDI nor audio I/Os work, IOW I noticed the above when I tested
the PreSonus in combination with the USB hub using Linux.

I'll return the PreSonus and try to find another card for usage with
Linux as well as with iOS.

Regards,
Ralf
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