I foresee two types of responses to this thread: "Yes we know that already", and "omg you must be mad". This thread is to tell the latter it can be done, as myself was apprehensive to actually doing it.
I needed something to check whether my PSUs have gotten noisy or not. One task is to confirm whether the PSU for my ONT modem is indeed dead, second one is to check whether I should replace my 10yo ATX PSU or not.
Long story short, the tools required are: Pretty much nothing except for external attenuation, which I simply used resistors in a 10:1 ratio as these power supplies are 12V. I first tried with a DC blocking capacitor, but decided to skip it later and reach lower bass (?) because 1) The DC blocking capacitor in the sound card is also doing the same job, and even without the DC capacitor, the voltage reaching the soundcard is 1.2V so it's safe anyway. When power on, the initial spike on some of the PSU just reaches 0dBFS for maybe one sample, so we are still pretty much safe.
Being a sound card, it does not tell you the actual voltages, although ARTA has the feature to calibrate your sound card. What I'm thinking of doing however is to measure a few reference voltages e.g. 1V, save it as a wav file, and then compare everything in Audacity.
For now I don't have the reference 1V yet but comparing the broken PSU (top) with other PSUs at no load it is clear that it is borked.
I needed something to check whether my PSUs have gotten noisy or not. One task is to confirm whether the PSU for my ONT modem is indeed dead, second one is to check whether I should replace my 10yo ATX PSU or not.
Long story short, the tools required are: Pretty much nothing except for external attenuation, which I simply used resistors in a 10:1 ratio as these power supplies are 12V. I first tried with a DC blocking capacitor, but decided to skip it later and reach lower bass (?) because 1) The DC blocking capacitor in the sound card is also doing the same job, and even without the DC capacitor, the voltage reaching the soundcard is 1.2V so it's safe anyway. When power on, the initial spike on some of the PSU just reaches 0dBFS for maybe one sample, so we are still pretty much safe.
Being a sound card, it does not tell you the actual voltages, although ARTA has the feature to calibrate your sound card. What I'm thinking of doing however is to measure a few reference voltages e.g. 1V, save it as a wav file, and then compare everything in Audacity.
For now I don't have the reference 1V yet but comparing the broken PSU (top) with other PSUs at no load it is clear that it is borked.
......And lead to someone looking at USB decrappifiers. 
tek310A