iFi PowerStation テクニカルノート Part.2 電源ノイズ。これこそが真の災いのもと。


Part 2: Mains noise. A real bane.
Power supply noise is the bane of every audio system. There are always multiple sources of noise and they come from two main sources – inside and outside.

External noise is all around



This chart shows that noise is anywhere and everywhere and some of it inevitably ends up in the mains that supplies the audio system. We can do little about most of these as they come from sources found in everyday life such as radios or mobile phones.

As these are wireless in nature, they are very difficult to deal with at the source, so we need to address the symptom.



The next chart shows the ‘local’ noise sources found in and around an audio system.


Local noise comes from hi-fi components
These sources of noise are found in hi-fi systems and come from three main sources:

  1. AC mains power supplies
  2. Switch-Mode Power Supplies
  3. Digital circuitry.



  1. AC電源
  2. スイッチング電源
  3. デジタル回路

(From left to right:)

The first set of noise sources (10k > 10MHz) relate to AC supply rectifiers and their harmonics caused by Linear Power Supplies (LPS). Yes, they make a noise!
The second set of noise sources (67k > 200 MHz) is caused by Switch-Mode Power Supplies (SMPS). By comparison, these harmonics run in the higher frequencies.
The third set of noise sources (8 MHz > 500 MHz) is caused by digital circuitry, clocks and their harmonics. And this type of noise exists in the most upper frequencies.
You can see from the chart that the concentration of noise is from 30kHz upwards (the lower the dB, the less influential is the noise).




It is worth noting that, as much as LPS designs get a good reputation and SMPS designs get a bad reputation, the reality is somewhere in between. And the situation is dynamic.

LPS designs are on the whole good and, on average, are quieter than poorly designed SMPS power supplies (which tend to be more for charging mobile phones and are not optimised for noise). This is why LPS is often perceived as superior to SMPS.




Hybrid and electric cars used to be shunned, yet they are now all the rage. We believe the same is happening for SMPS. These are now more environmentally-friendly and consume far less power. Whereas all SMPS used to be ‘noisy’, we are one of the few companies who have broken down the SMPS into its constituent parts and fundamentally re-designed it for audiophile use ie super low- noise. The iPower is the ‘Model 3’ of SMPS power supplies.


Nevertheless, not everyone has an iPower at their disposal. It is therefore important to be able to effectively deal with normal SMPS noise which can be quite severe.
The next section explains which aspects of the PowerStation target the different groups of noise and how this compares with the common approach.

Part 3 shows how active beats passive everytime.



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