Originally Posted by slim.a
have you compared the following (A vs. B) :
A/ Laptop running battery power + Teralink without external power
B/ Laptop running AC + Teralink with external battery ?
Are you basing your comments on theory or real A/B experience with your teralink-X ?
I use a desktop PC, I have tried running the Teralink off usb power and then switching to external power. I can notice a big diffence here.
Yes you are right there is no galvanic isolation, I was commenting on two things.
1) the person enquiring abourt running the teralink off battery, and
2) Your response, to that question, where I was just pointing out the that running off usb power is not the same as running the teralink directly off the battery.
You see, the 5V rail in the computer has many other ICs operating off this same rail, so there will be all manner of switching noise on this rail, and also on the ground rail. How bad this is exactly, i have not measured, but I suppose it would be safe to assume that the battery will have much less of this switching noise than the laptop.
Also, SMPS generates quite a large amount of EMI, so although the DC output of these power supplies might be quite smooth and stable, the proximity of the power supply to your computer and DAC may be affected by this EMI.
The external wall wart SMPS does not have metal shielding around it whereas the Desktop PC power supply is shielded by a metal case and then grounded. It would vary from power supply to power supply, but it would be resonable to assume that shielded is better than non-shielded.
Anyone else want to add thier oppinion, or some facts??