m00dawg Posted June 29, 2011 Report Share Posted June 29, 2011 I would describe it as transient noise that comes from the high frequency noise in the DC power output itself. The noise is caused by the high frequency circuity that is acting like an on/off switch flipping the source input on and off rapidly to end up with the output. It's a very efficient process - much more so than linear PSUs. They can also handle a wider range of input voltages because the switching circuits just switch at different rates depending on the input to produce the stable output. The trade-off is that what you really end up with is a bunch of pulses on the DC signal that look like a certain voltage overall (say 12V). Think of it as a somewhat ugly high frequency square-wave of sorts. The problem here is that the high frequency noise this creates cannot be totally filtered out without using capacitors that are built to dampen HF noise (such as tantalum). These can be both expensive, some say dangerous (I tend to disagree), and a bit of a black art. From what I have read, ceramics can reduce HF noise but this comes at a price. So you have to end up using various different types of caps. In the end, capacitors are not perfect and you may need to use quite a few to remove the noise, or may not be able to remove all of it regardless. Linear PSUs do not have this problem as the noise they generate is typically easier to filter out and it's usually HF (though I think if you have HF noise coming from the AC side, you may see some of that on the DC - not entirely sure though). All that said, if you're not hearing the noise, it could be too high pitched for your ears - either because you went to too many concerts without earplugs :) Or because the switching frequency of your DC supply is above the audio range (say 1MHz). In those cases, the noise is likely there but you and your audio equipment can't really pick it up. Some might call that a non-issue but I prefer linear PSUs just because I don't want HF noise of any kind in my audio signal, regardless of whether or not I can hear it. Plus I find them more interesting. TL;DR If you can't hear it, it's probably ok. Quote Link to comment Share on other sites More sharing options...
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