USB A to B cable shield connection, how? - diyAudio
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Old 21st April 2013, 11:33 PM   #1
piniu29 is offline piniu29  Ireland
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Default USB A to B cable shield connection, how?

Hello all.
I want to connect my DAC to a iMac in another room through the USB and control the music playback with Remote App on iPad. DAC is operating as an asynchronous USB Audio 2.0 class device, the USB receiver is Tenor TE8802 chipset with dedicated low noise power supply, and the distance between devices will be less then 6m.
After reading a bit about the USB standards I am a bit confused, some say it's better to connect the shielding at the side where the ground plane is the best (Host) and some say that shield should be connected to both sides but not connected to ground in any way?
I think that the cable braid and plug/socket shell must be connected to ground on at least one end, otherwise the shield become as a long antenna to radiated EMI, am I right?
What is the best design practice to do this USB A to B cable properly to reduce EMI/RFI interference?
Any help will be greatly appreciated.
Thank you.


photo of supra cat7+ cable and connectors
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Old 21st April 2013, 11:42 PM   #2
DUG is offline DUG  Canada
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Try one side only...listen to results...check with portable AM radio tuned to empty part of band...try both sides...listen to results...check with portable AM radio tuned to empty part of band.

I would connect both sides...but that is just me.

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Old 22nd April 2013, 12:53 AM   #3
qusp is offline qusp  Australia
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both sides, but just to the shell, as in just crimp the shell piece around the shield. the USB panel sockets shells should be connected to chassis/shield ground and this will connect the shield to chassis ground at both ends. it should not be connected to signal ground, USB ground or power supply ground itself at either end by any means but the disconnect network (which will, or should already be taken care of). its a shield, treat it as one. there is no argument about this matter by anyone who has actually read the standard...

what will you do with the extra pairs in the cat7?
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Old 22nd April 2013, 01:51 AM   #4
qusp is offline qusp  Australia
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Quote:
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its a shield, treat it as one. there is no argument about this matter by anyone who has actually read the standard...
my apologies, didnt catch that you had read the standards. it seems you have come up against the widespread confusion about interface grounding, its unfortunately widespread, I have no idea why, just the same as pin 1 on an XLR cable. it should be connected at both ends, but I suppose you cant rely on everyone to have followed proper protocol. Why people continuously confuse shield/chassis ground with ground I dont know
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Old 22nd April 2013, 02:36 PM   #5
marce is offline marce  United Kingdom
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Connect at both ends as Qusp and DUG have stated, trhat is the ONLY way to shield a cable. A cable connected at one end only does not shield, but makes a nice antenna.
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Old 22nd April 2013, 09:51 PM   #6
piniu29 is offline piniu29  Ireland
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This is why I love this place, thanks for your quick responses!

I did not know this technique with the AM radio tuned to empty part of band to “catching” the radiation, very interesting I must try.


You were right I was wrong by thinking to connect the cable braid and plug/socket shell with the (Pin 4 Ground) at one side and leaving the shield open on other end with the only wire (pin 4) connected!
I will do this correctly by connecting both ends, according to your recommendations with the braid terminated to the plug metal shells, as close to 360° as possible, to avoid EMI but not connected to ground(pin4) in any way.


one twisted pair as the data -, data+, another pair will be combined together to reducing the resistance of wire and connected to the pin 4 GND and the same will do with the Pin 1 +5vdc and one pair I left not connected.


I wonder whether the wire must be connected to 5V + according to the Burson website the USB receiver (Tenor TE8802) of the Burson Conductor DAC has its own dedicated low noise power supply, getting rid off the + 5V line of the USB may reduce the amount of electrical noise comes from the computer. What do you think, leaving as it is or disconnect?
What worries me more is the cable length it has to be about 6 meters to reach the computer in the other room, but the usb 2.0 spec says 5 meters, I hope that the supra cat7+ cable will let me pull to 6 meters?

Last edited by piniu29; 22nd April 2013 at 09:53 PM.
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Old 22nd April 2013, 10:56 PM   #7
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Just so ya know,I haven't had much luck with USB over longer cable runs.(ie: it doesn't work,for me.) IIRC,the spec is 3 meters max. cable length. Much longer than that,and I've had issues with devices not being recognized,and even seemingly power-related issues,I assume from voltage drop.

Has anyone else here had success making a USB cable longer than about 15 feet/3meters?
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Old 23rd April 2013, 02:29 AM   #8
DUG is offline DUG  Canada
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These are all commercial but there must be some cheap ones somewhere that work well.

USB to fiber:

USB Extenders over fibre
USB to Fiber Optic Modems (Media Converters) by S.I. Tech, Inc.
USB Extenders - Icron Technologies Corp.
A200 USB to Fibre-optic Loop Adaptor :: Introduction

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Old 23rd April 2013, 02:42 AM   #9
qusp is offline qusp  Australia
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or...gasp.....wifi
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Old 29th April 2013, 12:09 AM   #10
piniu29 is offline piniu29  Ireland
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Ok guys, just wanna let you know my recent findings. I finally had time to do this USB cable today, but before I will cut my cable(originally purchased a length of 12 meters) to the required length of what it needs I decided to try out the full length of the cable.
And it's working!
I tested so far, 12 meters USB A to B Supra Cat7+ cable connected to my Burson Conductor DAC with MacBook pro 2011, iMac 2011 and my very old Toshiba laptop streaming music from redbook to 24/192kHz without any hassle and finally tested the cable with the HP printer and it works like a charm.
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