# DIY USB A - B cable



## WALL-E

I didn't see any similar thread to this it would be very useful to have ours projects well documented step by step, why pay so much for "know-how"?
 This thread is dedicated for those interested in building their own cables.
  
 This will start with my latest project - USB A - B cable.
 I needed USB cable which meet the USB 2.0 spec over longer runs, as we know the maximum cable length is 5m I'll be back to this later.
 I always wondered why not use Ethernet cable as they are special designed to transmit digital data such as a USB cable through the current loop and it is also adapted for transporting the information at a much greater distance than the USB. So I chose the cable category (Fa) cat7 actually Cat7+is improved version of 7a, made by Swedish Supra Cables.
  
 Supra Cat7+ spec.
  

  
 The USB 2.0 standard defines a High Speed transfer rate of 480Mb/s.The transmission is done from a transmitter to a receiver through differential data line, to limit data reflection, the following must match:
 - Transmitter output impedance
 - Line characteristic impedance
 - Receiver input impedance
 The USB 2.0 standard defines a cable with 90Ω ± 10-15% differential impedance.The cable may have no more than 30 ns signal propagation delay on entire length.Cable is 4 wire.The data wires are 28 AWG twisted pair, the power wires are 20 to 28 AWG.The cable shielding must cover at least 65% overall.
  
 The Supra cat7+ have everything what I need to build my own USB cable. Excellent screening characteristics 100% coverage(individual and overall screen) for minimal interference, low delay skew, bandwidth 1300Mhz, low capacitance and efficient noise rejection maintain signal integrity in the long run interconnects, PE- insulated wires with the exact 100 Ohm impedance design in wide range.
  
 Note : This is a simple tutorial.
  

  
 As you see, the Ethernet cable consists of four pairs of conductors, each of the conductor pairs has its own shielding, in addition to the outer shielding, we will need only three pairs, one twisted pair for 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 we will do with the Pin 1 +5vdc, the remaining pair needs to be cut off.
  


  
 USB Connectors Pinout
 1. +5 VCC
 2. Data-
 3. Data+
 4. GND
  





  
 The braid is to be terminated (crimped) to the plug metal shells at both ends, as close to 360° as possible, to prevents EMI/RFI interference.
  
                                    
   ^ TEST BEFORE YOU PLUG ANYTHING IN ^
  


  
 Done! Here you go 2.5m high quality USB A - B cable at low cost.
 Hope this was helpful.
  
 reference - some useful links:
 http://www.usbmadesimple.co.uk/ums_6.htm
 http://www.interfacebus.com/USB-Interface-Description.html
 http://www.gbs-elektronik.de/fileadmin/download/manuals/TN_Choosing_USB_Cable.pdf
 http://sdpha2.ucsd.edu/Lab_Equip_Manuals/usb_20.pdf
 http://www.cypherinstruments.co.uk/applications/AN004.pdf
  
  
 P.S. About over longer cable runs: I tested so far 12 meters cable! (before I split it into shorter lengths) connected to my Burson Conductor DAC with MacBook pro, iMac and my very old Toshiba laptop streaming music up to 24/192kHz without any glitches or even single dropouts and finally tested the cable with the HP printer and it worked without hassle.
 It shouldn't work! It gave me a lot to think about.The cable quality does matter and parameters such as characteristic impedance is the goal, rather than esoteric materials.


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## tomb

Interesting.  Just an FYI, but the limiting factor on USB length is voltage drop.  USB is also designed to carry _power_.  A typical copper conductor at 28ga will drop one full volt at 500ma and 15 feet - a half volt at 250ma.


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## WALL-E

No doubt especially when the USB receiver is bus powered It should be taken into attention and use ticker wire for power lines. My one have enough "copper" in power lines each pair contains of 22awg connected in parallel, effectively reduces the voltage drop to min IMO.


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## tomb

Quote: 





wall-e said:


> No doubt especially when the USB receiver is bus powered It should be taken into attention and use ticker wire for power lines. My one have enough "copper" in power lines each pair contains of 22awg connected in parallel, effectively reduces the voltage drop to min IMO.


 
  Of course - 22ga - especially run in parallel - is exponentially better at limiting voltage drop over single 28ga.  Since the power wires are the limiting factor in USB cable distance, it would've been appropriate to mention that you upsized them to 22ga and ran them in parallel when making your claims about improved length over the USB standard. No offense, but I guess all I'm trying to say is that "cable *quality*" really had nothing to do with it.


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## WALL-E

USB over long distances Cont'd.
   
  I did not mention this in the main thread the main reason why I started to look for best suited for this purpose cable was the distance between iMac and my DAC, 6m in a straight line I haven't had much luck with USB over longer cable runs I've tested generic USB2 cables bundled with printer, camera etc. I have lying around in my apartment, simply it doesn't work for me, much longer than that (1.5m + 3m) and I've had issues with devices not being recognized. To be honest Burson Conductor DAC USB does work without power from USB, like most modern DAC nowadays have the USB receivers an independent from 5V DC power from computer USB, what he need to work is just D+/D- line and GND.
   
  Power wires are the limiting factor in USB cable distance doesn't change the fact that cable quality has an impact too. The issue with the cable length is related to signal quality, right cable will (do) probably push it over the 5m limit. After I had success making a USB cable longer more than twice the max limit I cut it off to the length of 8.75m, this is my primary set-up now. iMac(audirvana)>>Supra Cat7+ 8.75m USB A to B>>Burson Conductor>>navigate with Remote App on iPad.
   
  I did a cable test which allowed me to extract the another limiting factor on USB length. I've used the fourth pair of conductors (normally not connected) and soldered to the existing one D+/D- data line, ran them in parallel. This cause the impedance (mismatch) drop by half. The USB 2.0 specification defines a 90-ohm nominal characteristic impedance. If every component in the chain (transmitter - line - receiver) is designed with a 90-Ohm impedance, there won’t be any reflection and there won’t be signal energy loss due to reflection in theory.
  so what happened?......by doing this, the exact characteristic of cable impedance has been disrupted increasing signal reflection as a result the devices not being recognized on Toshiba laptop and with the Mac not working at all. The same way I've tested my 2.5m USB cable shown in this tutorial, this time was better the device has been recognized, but not working properly intermittent dropouts and disconnecting.

 Summarizing characteristic impedance about 90 ohms as uniform as possible, right ga of power wires the quality of the connector and cable assembly shielding, quality of the cable shielding both EMI/RFI should be kept as small as possible all of does matter in terms of usb length.


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## Kamakahah

Thanks for the tutorial. I'll try this soon.


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## ben_r_

Awesome thread, but did I miss somewhere where you got your USB connectors from?! Links to parts and supplies would be useful for those looking to do this themselves.


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## WALL-E

Quote: 





ben_r_ said:


> Awesome thread, but did I miss somewhere where you got your USB connectors from?! Links to parts and supplies would be useful for those looking to do this themselves.


 
  Thanks, I ordered them from DHC link below,
  http://www.doublehelixcables.com/store/index.php?main_page=product_info&cPath=4&products_id=68


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## ben_r_

wall-e said:


> Thanks, I ordered them from DHC link below,
> http://www.doublehelixcables.com/store/index.php?main_page=product_info&cPath=4&products_id=68



Thanks!


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## stino

Hi, where did you source the Supra Cat7+ cable?


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## WALL-E

stino said:


> Hi, where did you source the Supra Cat7+ cable?


 
 I bought it off ebay http://www.ebay.ie/itm/Supra-CAT7-Network-Cable-Unterminated-per-Metre-/301154615865?pt=UK_Computing_NetworkingCables_RL&hash=item461e36c239
 if you looking for a USB connectors too, you can get them from Parts Connexion,10$ for a set.


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## stino

Great, thanks! I have some connectors already. Next time I order with PC I'll check them out.


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## axeltow

tomb said:


> Of course - 22ga - especially run in parallel - is exponentially better at limiting voltage drop over single 28ga.  Since the power wires are the limiting factor in USB cable distance, it would've been appropriate to mention that you upsized them to 22ga and ran them in parallel when making your claims about improved length over the USB standard. No offense, but I guess all I'm trying to say is that "cable *quality*" really had nothing to do with it.


 
  
 Hi guys, just wanted to bump this thread.
  
 I have a desktop mic that has a terrible buzzing sound. When i put the diy usb cable i got from a dac i purchased some time ago the buzzing goes away. Hence, I wanna make me a good shielded USB A to B cable but I have the following questions.
  
 What cable should I get if I do not want to use a Cat7 ethernet?
 What to do you mean run 22ga in parallel? Are you talking about a coaxial cable? Then what do you use for D+/- ? How do run it in parallel?
 The custom I have has actually two cables going into both connectors and a third slim silver one. From what I remember these were coaxials but I have no idea how they are soldered.
  
 What I really want to know is what cable should I purchase exactly 
  
 Thank a bunch


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## WALL-E

axeltow said:


> Hi guys, just wanted to bump this thread.
> 
> I have a desktop mic that has a terrible buzzing sound. When i put the diy usb cable i got from a dac i purchased some time ago the buzzing goes away. Hence, I wanna make me a good shielded USB A to B cable but I have the following questions.


 
 I'm not sure if I understood you correctly but for me it looks like ground loops problem rather than faulty usb cable but I can be wrong.


axeltow said:


> What cable should I get if I do not want to use a Cat7 ethernet?
> What to do you mean run 22ga in parallel? Are you talking about a coaxial cable? Then what do you use for D+/- ? How do run it in parallel?
> The custom I have has actually two cables going into both connectors and a third slim silver one. From what I remember these were coaxials but I have no idea how they are soldered.
> 
> What I really want to know is what cable should I purchase exactly


 
 I choosed Ethernet cable for one reason, length, length....., much over 5 meters and low cost of course. It has all parameters to make it possible on distance above 5 meters, like constant impedance over a wide range, wide bandwidth and very low attenuation.
 I don't know how long cable u will need if shorter then 1.5 meter I would not recommended Ethernet cables, not they are bad but they are stiff.
 Go for flexible 90 ohm data cables like this one http://wire-cable-tubing.wireandcable.com/item/coaxial-wire-cables/90-ohm-usb-aerospace-cables/w-3627-26
  
 No I talked about cat7+ and spare pair of conductors which I combined together to reduce the resistance in power line.


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## axeltow

OK, this was what I thought. Now it makes sense to me. Thanks a lot!
  
 Btw, I see you have combined orange,white and green, white for the ground and power. So coloring doesn't matter? I have some ethernet cable lying around so I will give it a shot. Around 2 meters is what I need but I can go with less as well.
  
 Ground loops you say? On the cable? I have all my equipment into a power strip which is connected to a surge protector which then goes into a grounded socket. When I actually discovered the cable was fixing the issue, I was on a laptop not connected in a different room.....I made all sorts of experiments


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## WALL-E

axeltow said:


> OK, this was what I thought. Now it makes sense to me. Thanks a lot!
> 
> Btw, I see you have combined orange,white and green, white for the ground and power. So coloring doesn't matter? I have some ethernet cable lying around so I will give it a shot. Around 2 meters is what I need but I can go with less as well.


 
  Yep that's right, look they are the same twisted in pairs. Within pair of twisted cables color doesn't matter, on condition, if you use for example (white&orange) for power combined together (in order to reduce resistance and voltage drop) soldered to the pin 1 of the type A connectot  u have to do this the same on the other end with type B connector pin 1(white&orange) this analogy also applies to GND pin 4 (white& green). Data  D+/D- in my case is blue an white.
  


axeltow said:


> Ground loops you say? On the cable? I have all my equipment into a power strip which is connected to a surge protector which then goes into a grounded socket. When I actually discovered the cable was fixing the issue, I was on a laptop not connected in a different room.....I made all sorts of experiments


 
 I thought rather the ground loop it can make somewhere between laptop and other equipment and the short 10cm usb is just a link but I can be wrong, anyway is worth to try and run the laptop on battery and see what happen.


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