From the labeling and max output specs, I would be guessing that there's an LDO inside (or maybe even a plain 78xx/LM317) to bring analog supply voltage to about +7..7.5 V.
Where the DC/DC for phantom power supply would be connecting is anyone's guess. What makes you think that ripple is a problem?
Hi thanks a lot indeed for your both very kind and helpful reply.
Let me make an introduction.
My main and almost only interest are usb audio interfaces.
For me low distortion and low noise are everything.
I am also a little annoyed by some many listening opinions i have read.
So i decided to try to finally measure something myself with my pc.
I have found this Arta software that i understand it is good quality.
The only measurement that i have been able to perform until now is the noise measurement.
So i am measuring everything i have at hand.
Another aspect that i do not like are usb powered interfaces.
So i bought one with external dc adapter. i should receive it very soon.
I will test it with the stock power supply, a cheap smps.
I do not know how much the noise will be.
So my idea to test it with a better power supply, linear or smps.
For sure i will test it with anything i have already at home just to see for any benefits in terms of lower noise.
Of course a really cheap and nasty SMPS may have excess ripple, but IMHO the main reason for SMPS nastiness is common-mode noise.
Most of that should be drained over the USB shield here, so unless you've got a ground loop running over that (i.e. unbalanced connections) you'll probably be fine.
Otherwise you could still try a plug-pack type supply of decent quality, but nobody will guarantee you that this quietens down the ground sufficiently
Thanks a lot indeed for the very interesting advice.
I guess the only way to check these possible issues is with measurements.
I will measure in every possible way to find the solution that with the same interface will give me the lowest noise.
From what i have read galvanic isolation from the pc could be beneficial because the power in the usb bus is dirty. Actually when i see something usb powered i am a little puzzled ... 5V/0.5A dirty do not leave much to play with. Much better 12V/2A with some uV of ripple.
But i understand there is no substitute for a direct measurement.
I am very curious to see how low i will go ... with a very cheap interface.
Thanks a lot again, gino