DF96 suggests exactly the opposite- buy a ready-made inexpensive USB cable and be done with it. The connections and impedances will be correct for the application. It may be less "fun" than randomly soldering and cutting, but it has the virtue of working correctly.
As a side note, if you indeed do understand nothing of basic electronics, you have to be a bit selective about whom to listen to. There are plenty of "gurus" and "guru-wannabes" out there who can sound knowledgeable to someone without a solid background in fundamental engineering. From what you've written here, you may have been led a bit astray by not particularly competent people with something to sell.
Only the guys who work with this stuff professionally in fields more critical than hobbyist audio.
When you are using a desktop PC with an IEC mains earth, there is a potentially
degrading earth loop due to screen and 0 volts ( black wire) being often internally connected in the USB device. I get best results by disconnecting the red +5V wire at the USB-A plug at the PC end of the USB cable, and not connecting the shield from the incoming cable's USB socket to the shield of the USB device's USB socket..
This works very well, at least with audio stored on USB memory sticks.
I also fit a 47 ohms .5W resistor in the 0 volts line between sockets, although I haven't tried short circuiting that since breaking the screen lead between sockets on the USB power supply, which uses a JLH ripple eater for ultra clean _5V power from a normal 1A + 5V linear PSU.
Alex
degrading earth loop due to screen and 0 volts ( black wire) being often internally connected in the USB device. I get best results by disconnecting the red +5V wire at the USB-A plug at the PC end of the USB cable, and not connecting the shield from the incoming cable's USB socket to the shield of the USB device's USB socket..
This works very well, at least with audio stored on USB memory sticks.
I also fit a 47 ohms .5W resistor in the 0 volts line between sockets, although I haven't tried short circuiting that since breaking the screen lead between sockets on the USB power supply, which uses a JLH ripple eater for ultra clean _5V power from a normal 1A + 5V linear PSU.
Alex
It may not be that simple if using another cable to the DAC. You may need to connect the earth from the linear PSU to the screen of the outgoing socket.
I presume that you wouldn't be using the same mains socket for this gear, as the PC uses ?
I use the present method also for playing high quality .wav files stored on USB memory, into the USB socket of an Oppo 103 which also benefits from an external low noise +5V USB PSU due to it's use of SMPS PSU.
Alex
In the case of a USB memory stick plugged into an adjacent socket in the PSU case, it isn't needed, and avoids that earth loop problem. As usual, you are talking theoretically without trying these things that have been verified by others too.
I have already stated in my 2nd reply that if the output socket has another USB cable to an external device plugged in, that you may need the earth from the Linear PSU connected to this socket. I should have said will need.
Most people try to keep mains supply sockets for DACs and the PC itself separate.
That is not my logic. My logic is that a USB cable made from the correct characteristic impedance (as required in the USB spec, and presumably supplied in any shop bought cable) must be superior to anything less than this, however cheap or expensive it may be.rojo said:
I assume you don't know what a cable characteristic impedance is? You don't know how to calculate it or measure it, or what effect getting it wrong has?
Fair comment Sy..
Placebo effect can be come into play.
I feel the discussion has descended into something it was never intended to be.
I was only sharing my impressions of a cable I made up that someone may find useful if using Dacmagic . For me the cable works and i'm quite happy with it.
Of course I have no facts and figures to back me up but just proffering the idea to interested parties to try and maybe subjectively evaluate.
Perceived wisdom and cold scientific facts surely only go so far...and then what?
Placebo effect can be come into play.I feel the discussion has descended into something it was never intended to be.
I was only sharing my impressions of a cable I made up that someone may find useful if using Dacmagic . For me the cable works and i'm quite happy with it.
Of course I have no facts and figures to back me up but just proffering the idea to interested parties to try and maybe subjectively evaluate.
Perceived wisdom and cold scientific facts surely only go so far...and then what?
Screens are put on cables for a reason, usually RF shielding theses days, but as usual I must bow down to Audiofoolery, no things I work on including USB are only tested for EMC immunity etc. often to standards way above that required for commercial gear, so as I said the shield is there for a reason (probably shielding) if you have a ground loop problem sort it.
Then we abandon physics and enter the world of Audiophile design, where you don't need to know anything, just bodge and play
IIUC the suggested modification was motivated by sorting out the loop problem, IMO dangerous to the equipment. What other ways would you suggest? I find this a rather important question.
You could start off by reading up on Henry Ott and Tony Waldron. Then you could draw out a schematic of all your interconnections and look at possible routes for the low current signal to travel down as it likes the path of least resistance, then you can sort the problem. Either by galvanic isolation between your equipment or proving a low resistance route via the interconnects for the low frequency signal that is likely to cause the hum. It is hard to give a generic answer.
What I don't do is touch my protective earth connections, nor do I condone any other method of protective earth connection other than wire to bare metal.
Tony Waldrons EMC rants and raves are quite a good read, as is some of the stuff on the EMC site of Keith Armstrong (compliance club).
One cause is having a relatively high resistance screen on your shielded IC between two pieces of equipment compared to the protective earth loop, if you have gone to great lengths to create star of star grounding you will often get duplicate current paths and thus a loop formed where some resistance will cause this excess current to be superimposed as a voltage on your signal causing that lovely mains hum.
That said the screen on USB and other bits of wire is again there for a reason, if you want to screen against RF you need to do it properly otherwise you are wasting your time, and screens connected at one end don't work for RF.
But anything I say will pale into insignificance as we are discussing making a USB cable where even a tiny understanding of LVDS, impedance matching etc. is missing...
For my own system I use wireless to stream from the PC (music server) to my Logitech squeezeboxes' so I don't have that connection to worry about.
What I don't do is touch my protective earth connections, nor do I condone any other method of protective earth connection other than wire to bare metal.
Tony Waldrons EMC rants and raves are quite a good read, as is some of the stuff on the EMC site of Keith Armstrong (compliance club).
One cause is having a relatively high resistance screen on your shielded IC between two pieces of equipment compared to the protective earth loop, if you have gone to great lengths to create star of star grounding you will often get duplicate current paths and thus a loop formed where some resistance will cause this excess current to be superimposed as a voltage on your signal causing that lovely mains hum.
That said the screen on USB and other bits of wire is again there for a reason, if you want to screen against RF you need to do it properly otherwise you are wasting your time, and screens connected at one end don't work for RF.
But anything I say will pale into insignificance as we are discussing making a USB cable where even a tiny understanding of LVDS, impedance matching etc. is missing...
For my own system I use wireless to stream from the PC (music server) to my Logitech squeezeboxes' so I don't have that connection to worry about.
marce, thanks a lot for your extensive answer. I really would like to explore this issue, not for the tweakers, but for those who experience a ground loop problem in their setup - like rojo does with his lights on/off
Well, this is USB, rather expensive to isolate.
E.g. adding a thick wire to complement the ground wire of the USB cable?
Yes, and I would not even cut the USB grounding wire for above stated reasons of different voltage potential.
Tony Waldrons EMC rants and raves are quite a good read, as is some of the stuff on the EMC site of Keith Armstrong (compliance club).
Again, could a thick ground wire paralel to the shield help?
I thought a star ground topology was the desired outcome...
Point to be learned.
Well, that is a different story
Thanks a lot for your expertise, ground loops are ugly beasts many people fight.
Well, this is USB, rather expensive to isolate.
E.g. adding a thick wire to complement the ground wire of the USB cable?
Yes, and I would not even cut the USB grounding wire for above stated reasons of different voltage potential.
Tony Waldrons EMC rants and raves are quite a good read, as is some of the stuff on the EMC site of Keith Armstrong (compliance club).
Again, could a thick ground wire paralel to the shield help?
I thought a star ground topology was the desired outcome...
Point to be learned.
Well, that is a different story
Thanks a lot for your expertise, ground loops are ugly beasts many people fight.
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