Thank you everyone who have provided your valuable comments so far.
The intent of the isolator is to:
1. Break any ground loop to reduce noise.
2. Provide ample, quiet power.
The isolator will not guarantee an audible improvement in all situations.
However, in situations where a USB DAC is struggling, it can provide
a dramatic improvement.
It can be run from a battery, however it was never designed to be
power efficient. A 7.2 vdc battery would work if the bridge rectifier
is not used, a 9.6 to 12 volt battery would be needed if the bridge
rectifier is left in place. You would want at least a 2 A/H battery
capacity to get reasonable run time.
While adding a DC output jack may seem like a value add, I feel
it may cause confusion with some user and could result in equipment
damage. For those who wish to hack, 5 vdc is conveniently available
from the test points on the board. This also bypasses the 500mA
The two LED's are used to set the output voltage and give the
design very low noise compared to other LM317 designs.
It should be possible to use one as a power indicator, but
this has not been tested and the extra lead length may lead
to unpredictable results. Again, a power LED could be added
at the test points if two LED's inside the case are not enough.