RFI Management – Noise In The Machine


We have of course, also talked about Radio Frequency Interference (RFI) as being another major culprit in the destruction of good performance. But again we need to get our thinking into the right form. One of the first myths to dispel, we think, is the idea that the mains is simply about getting our AC power out of the wall and into our hi-fi. Well that does happen of course, otherwise our hi-fi wouldn’t work, but there is a lot more going on than that. Once we plug those leads into our system we have also provided a very efficient network to feed electrical noise (and that vibration!) in and around our system.

So let us look again at our system schematic, only this time consider where the RF noise is. Where the noise is doing the damage of course, is when it gets inside our boxes of electronics. And remember, that whilst we naturally think of the power going into our system on the live and returning back down the neutral, thats only one signal at 50Hz (or 60Hz). At much higher frequencies, the live, neutral and earth are all picking up rubbish (from computers, mobile phones etc) and transporting it around. One more thing to consider, the noise flows both ways – your boxes are noise generators in their own right and they output noise onto their mains cables, often polluting other parts of the system.

A system with a lot of internal noise generators (CD players, DACs, amps with switch mode power supplies, or class D amps etc.) can be much more difficult to manage in RF terms than an inherently quiet system (such as vinyl front ends and analogue amps etc. (but that doesn’t mean they can’t suffer more from other issues!)).

Vertex AQ Systematic Approach – RFI Management
Fig 4 – system noise diagram – click to enlarge

So in figure 4 we have changed the emphasis of our schematic and now it represents what’s happening with RFI in and around the system. At the moment in our system, we are doing nothing about the RF noise, therefore we are showing it at a high level throughout the system.