DIY solid core audio USB cable with linear power injection

Disclaimer: 

Please note, this is an information thread only. 

I accept no liability for damage caused by the implementation of this cable design, incorrect termination and/or use of this cable design. It works for me and my HiFi friends and has done so for many years. If you are going to copy this design, you do so at your own risk. I can only suggest be careful with your terminations and double / triple check continuity to ensure you don't damage your HiFi computer equipment. 

This blog in a few short steps will show an overview of how to make a linear powered DIY solid core USB lead.... We will be breaking out the power (5vdc +) and ground (gnd) connections, from the type B USB connector end to enable a linear power supply connection.

Why bother you may ask? Well if the quality of the 5vdc USB power source can be improved, we can yield quite noticeable improvements in USB sound quality and USB device rendering performance. 

On implementation the most obvious benefit will be a subjective increase in detail and reduction in grain through the midrange and high frequency spectrum. Additional benefits in fidelity / transparency / overall spectrum detail / soundstage may also be noticeable, depending on the transparency capability of your audio system & ultimately your ear.

HOW? 
We need to remove the dirty '5vdc feed' produced by your PC (on pins 1 & 4 of the type A USB end) and replace it with a more linear 5vdc supply from the source of your choosing. I personally use this power supply (Teradak linear power supply 0-9vdc adjustable... please note the unit now comes with a USB 5vdc output, making DIY super easy). 

Not keen on starting a cable design from scratch? Too Difficult? Maybe try this simplified design........ CLICK THIS LINK.... The blogpost explains how to 'easily' modify a standard USB cable to accommodate linear power injection. 

So lets get started.

STEP 1.... SELECT YOUR CONDUCTOR TYPE 

Firstly select your signal conductor metal of choice. In this DIY build, I am using solid core silver (22 awg). Possible alternatives, would be UTP copper twisted pairs for instance (especially if you would like a decent level of emi/noise rejection in your design.. 

My advice is try a few different types of core conductors and/or combinations to achieve a sound that suits your system. 

STEP 2.... MAKE SURE YOU HAVE THE FOLLOWING
You are going to need the following items to make your DIY solid core, linear power USB lead..... 
1 x Type A terminating USB connector
1 x Type B terminating USB connector
1 x LED (I used 2.1v rated LED)
1 x Resistor to suit your LED rating 
1 x Some heat shrink / solder for terminations
1 x PVC / Teflon tubing / Heat shrink for Jacketing
1 x Soldering iron 
Some signal wire
1 x DC plug. 
1 x Your Time 

Note: the Teralink power supply I used came with a basic copper DC power lead, which I de-soldered the connectors from. If you are making your own DC lead from scratch, the DC sizing is as follows, 5.5mm outside / 2.1mm inside.

If you are unsure on what resistor and LED values/combination to use... Simply use an LED calculator similar to this (LED resistor calculator). Personally I used a single 100ohm resistor, and the following LED from Radioparts rated at 2.1 forward voltage / Forward current 30mA.... I hope this helps. 

http://www.radioparts.com.au/ProdView.aspx?popup=1&Category=SXLL44&Product=27940025&ProdDesc=LT521+GRE-LED+DIF-5MM+1.5MCD

Alternatively, I have read a single 1/2w 220ohm resistor (replacing the LED and single resistor) would do the same trick. Termination would be between 5vdc+ and Ground. 

STEP 3.... SOLDER YOUR WIRE 
This cable will require direct solder of signal cores between the type A and B USB connections, however as we will be powering the SPDIF device from linear power, connections 1 & 4 from the type B connection will be connected to a DC plug/or your alternate power source - not the USB type A connector (on the other end of the cable). 

Click here for a wikipedia - usb type & pinout guide

FURTHER PINOUT INFORMATION 
To help you locate the correct USB pins for termination. 

USB PINOUT KEY 

Pin 1  +5vdc 
Pin 2   Data - 
Pin 3   Data +
Pin 4   Ground  

So this is what you should have; 

Connector Type B (The square looking connector) 
Spdif converter end 
1 Power + which will connect the the centre of the dc connector 
(solid CAT 5 core, the power cable used has little effect on the signal quality) 
2 Data -  > Connection to Type A pin 2 (solid silver in this build) 
3 Data + > Connection to Type A pin 3 (solid silver in this build) 
4 GND which will connect the the sleeve of the dc connector
(solid CAT 5 core, the power cable used has little effect on the signal quality) 
5. Connector shell > terminate to Type A connector shell - 
This termination may be required for some PC's. For instance my MATX PC worked fine without the connectors grounded, however my i5 laptop required both Type A and Type B USB connectors to be grounded for the USB signal to initiate.....  

Note, CAT 5 cores were used for power.... These feeds don't require silver. 
Copper does a fine job carry the low voltage 5vdc feed.\

Connector Type A (The flat looking connector) 
Spdif converter end 

1 Resistor leg (No polarity here, so choose a leg >Terminates to > LED + (anode) 
2 Data -  >Terminates to> Connection to Type A pin 2 
3 Data + >Terminates to> Connection to Type A pin 3
4 LED leg - (cathode) Terminates directly to USB pin on connector  
5. Connector shell > terminate to Type B connector shell
Refer to my comment above in red. 

STILL UNSURE ABOUT WHICH PIN IS WHICH 
Just incase you are a little unsure about the pin placement on the usb connectors. I have cut up an old DIY usb lead (not this build), to help detail which pin is which on each of the type A and B connectors. I hope this clarifies. 

To prevent any confusion, the type A and B connectors below are orientated as per the pin detail above. 

In these pics, the key is: 
Pin 1  +5vdc      GREEN 
Pin 2   Data -     BLUE/WHITE
Pin 3   Data +    BLUE
Pin 4   Ground    GREEN/WHITE

Note: I have curled the blue/white conductor to help identify the core colours easier.

RESISTOR HELP 
The resistor and LED are used to trick your computer into thinking it is powering the usb device (your spdif converter)...... Many computers will not allow data signal to pass until a power draw is measured and active. 

If you are having trouble figuring out which end is the cathode and anode of your LED refer to the pic below. In short, the long LED leg is anode, and the shorter LED leg is the cathode (Flat side of the LED). Note, the resistor does not have polarity, so this is not important when terminating as above. 

LED POLARITY 

Link to wikipedia led polarity

STEP 4.... COVER IT UP!! 

I am going for sound quality, so my cable jackets and coverings are pretty basic. In general I tend to utilise a combination of polyester sleeving and/or heat shrink to dress my cables. 

You may notice my silver DIY cable design does not employ braided shielding, this will undoubtedly upset a few technophiles. Please note; I don't advocate for an absence of shielding in a USB design, and the ability to run a non shielded cable will be highly system dependent. These photos are for illustration purposes. 

Alternatively a copper twisted pair design (as below) retains the UTP twist offering decent EMI rejection. You will see an example of this below, I have foil wrapped the signal wires for added shielding. 

Either design subjectively provides improvements in sound quality when compared to traditional standard (non linear powered) USB cables. I would however suggest when DIYing a USB cable to keep it as short as possible, to reduce possible interference issues. My cables are typically no longer than 300mm, shorter is even better. 

CHECKING TERMINATIONS
At this point, double and triple check your connection terminations are pin to pin!!....You don't wont to blow up any USB controllers, etc in your PC or audio device.

Do this with a multimeter. Pin to Pin testing, will ensure there are no incorrect terminations or shorts to the body of your Type A or B connectors. Remember to test Pin to connector shell - just to make sure. 

Testing from Type B USB connector 
Pin 1 - Should continuity test to power positive connector
Pin 2 - Should continuity test to USB Type A pin 2 
Pin 3 - Should continuity test to USB Type A pin 3 
Pin 4 - Should continuity test to power ground connector 
Connector - Should continuity test between Type A and Type B connectors if implemented 

Once your cable has been thoroughly tested with a multi-meter and you are satisfied with your terminations, plug the cable in. 

If you have a working LED when you plug in your cable (when your PC is on) your LED "trick load" is working as it should. Your PC should now also see the device! provided your 5vdc power supply has been activated. 

WRAPPING UP 

I believe this DIY linear USB cable mod provides a great alternative to pricier battery powered interfaces which although offer similar improvements in sound quality are significantly more expensive to purchase. In my opinion (and of some HiFi friends), a well made linear powered DIY USB cable (Cooper or Silver) will be one of the most significant investments in sound quality you can make for your usb spdif/aux device.

I am confident this DIY linear power cable design will be 'the USB cable' by which your future and current USB cable designs/purchases will be measured . So for now, until I find or build something better, my DIY solid core silver/copper linear powered USB lead will continue as my reference cable. 

Can I suggest to any technophile doubters out there, who question this design to please try before commenting? you might be surprised, injecting clean linear power and using solid cores for signal transmission may have some validity?! ;) 

Thanks for reading..... I hope you enjoy your new USB cable...