Pelliott321 wrote:
I found this on the DIYAudio Forum
https://www.diyaudio.com/forums/analog-line-level/354213-po89zb-inline-dc-filter-smps-wall-warts-preamps-hpa-korg-nutube-etc.htmlfrom the dialogue, this seems to be blessed by Nelson Pass and is a very simple circuit
Attachment:
SMPS_filter_schematic_revA.png
This will work as a filter and will probably be better than nothing but there are a few things I would do differently:
D1 appears to be a varistor used as a clamp. However, it is rated at 68V with a maximum clamping voltage of 145V. If that voltage were reached, everything downline would probably be toast. In reality, I don't see the need for a varistor on the output of most wall wart power supplies.
The chokes used are only 2 uh which in conjunction with the capacitors used will have a turnover frequency much higher than the combination of the 2.5 mh choke I'm using in conjunction with much higher capacitance. This circuit will filter out the highest frequency noise but will not be effective at lower frequencies. How that will affect the sound I don't have a clue. It will depend on the circuit being fed.
All the capacitors used are electrolytics which are not very good at filtering out high frequencies. Remember that the monolithic ceramics I use on the output are doing double duty, not only filtering anything that might get to the output from the power supply side but also reducing any high frequency noise generated by the buck regulators internal to the NUC. You can see how the output of the linear power supply had the noise reduced by the addition of the filter. The linear supply probably could not reduce the noise being generated by the buck regulators.
The high amount of capacitance in my version also serves as a huge current sink so that any current pulsed caused by the bucking regulators will not affect the voltage on the input to the NUC nearly as much as the smaller storage in this circuit. Will it matter? Who knows?
One thing for sure, the circuit I am using is certainly bullet proof and may be overkill, but it is simple and cheap. In reality, this circuit seems to be no simpler or more complicated than the one I am using. Both should be a slam dunk for any DIYer to build.