Re: Filter for switch mode power supplies
Posted: June 1st, 2021, 11:12 am
Someone asked me to compare the switcher/filter combo with a linear supply. I did the test of my lab grade linear power supply feeding the NUC directly. Before listening, I ran some scope traces of the power at the input of the NUC both straight from the supply and also with the filter in place. You can see that the unfiltered voltage is actually quite good with no major spikes but rather what appears to be random noise reaching about 50 mv at some places. It did not look as good as the switch mode supply with the filter but a whole lot better than the raw switcher. The supply itself had lower noise than shown when connected to the NUC but it appears the linear is not as good at filtering the noise from the input of the NUC as the filter. I also took measurements with the linear and the filter and it looked virtually identical to the filtered switcher.
I listened to the lab power supply without the filter and then the switcher/filter combo with the same test tracks I used before. To make a long story short, the linear supply unfiltered sounded basically the same as the switcher filtered. If I were splitting hairs, I would say the filtered switcher was slightly better at some points having a little more air and separation, but the differences were so small I would not want to try a blind test. It would probably take a lot more music trials and additional listeners to see if there was truly a difference. I did not try the linear with the filter because even unfiltered the results were so close if not identical that it was not worth the effort. In either case they were both significantly superior to the raw switcher. My take away is that as long as whatever supply is being used has enough voltage and current capability to run the NUC, the filter levels the playing field as far as sound is concerned. Certainly, the filter is a cost effective (if you are a DIYer) way to improve the sound of the NUC. I'm sure there are much better servers available that cost much more than the NUC that may have superior power supplies, making an external filter unnecessary. However, this combo represents great value. Charlie has a custom built server that Jim raves about. Jim says he will try to borrow it so we can compare to the NUC/filter combo. It will be interesting if it happens.
I listened to the lab power supply without the filter and then the switcher/filter combo with the same test tracks I used before. To make a long story short, the linear supply unfiltered sounded basically the same as the switcher filtered. If I were splitting hairs, I would say the filtered switcher was slightly better at some points having a little more air and separation, but the differences were so small I would not want to try a blind test. It would probably take a lot more music trials and additional listeners to see if there was truly a difference. I did not try the linear with the filter because even unfiltered the results were so close if not identical that it was not worth the effort. In either case they were both significantly superior to the raw switcher. My take away is that as long as whatever supply is being used has enough voltage and current capability to run the NUC, the filter levels the playing field as far as sound is concerned. Certainly, the filter is a cost effective (if you are a DIYer) way to improve the sound of the NUC. I'm sure there are much better servers available that cost much more than the NUC that may have superior power supplies, making an external filter unnecessary. However, this combo represents great value. Charlie has a custom built server that Jim raves about. Jim says he will try to borrow it so we can compare to the NUC/filter combo. It will be interesting if it happens.