Power or Line Conditioners
Lots of people are getting sold expensive power conditioners in recent years. They are a very profitable product for many retailers. I have found that many of them can be very effective in reducing line noise. The rest of the story, however, is that this noise is almost never a problem that affects the performance of your system. In many cases, users report improvements when installing them. Some of these improvements are real, and some are due to expectation bias or placebo effect. When an improvement actually does occur, it is often due to bringing all of the grounds in the system to the same potential when the signal lines are connected at the surge suppressor. The fact is, in most of these cases, that a much less expensive unit, or just improving the grounding in the system would have achieved the same effect. The dangerous part is that if the system is not grounded at the entry points to the home properly, surge suppression is less effective and the system may be at risk in the case of a severe lightning strike, power disruption, or surge.
The bottom line is, don't assume you need sophisticated filtering. Do the basics first and see what you can get for free (grounding), since this is important regardless of the purchase. Try a less expensive solution if problems remain, and only use expensive line conditioners if you must, or if you just want the cool lights and meters. There is nothing wrong with buying something because you think it is neat or it makes you feel better, but everyone should understand that most line conditioning is not going to improve your pix.
So why do I say that filtering noise is of little or no benefit? Well, modern electronics, with the exception of audio amplifiers, almost always use SMPSs (Switched Mode Power Supply). These supplies take incoming a.c. and rectify it and filter it like a conventional power supply. Then the d.c. is switched on and off through a transformer designed for this purpose at a rate of typically 50 -150 kHz. This creates a nasty looking pulse waveform that has to be rectified and filtered again to provide the d.c. that the various circuits need. After that, it is typically further filtered and regulated again. The noise on the a.c. line typically never survives the primary side filtering, and is even less likely to pass through the switching transformer. Even if it does, it is at such a low level compared to the switching pulse itself that it is insignificant. The rectifier and filter in the secondary will have to reduce this nasty switching pulse that is hundreds or thousands of times more energy to d.c. and filter its remnants. The noise from the a.c. line is simply not a factor. The rectifiers in the secondary of the SMPS are usually very fast recovery diodes, followed by capacitors and inductors to clean the line. It usually is then regulated again to provide the voltage that each circuit needs, and filtered some more. With SMPSs, there are also usually large inductors on the a.c. input to keep that noisy power supply from feeding back in to the power system and affecting other equipment.
So what about the line noise? How do we know that it can't somehow survive the conversion in the PS? All logic, theory, analysis, and reasoning is based on assumptions, and decades of experience has taught me to never rely solely on what "should" happen because you will probably have missed an assumption, or something that was believed to be insignificant turns out to be a real matter. So I look. I have lots of equipment in the shop, and some generates a good bit of noise, so I can often see noise on my bench a.c. lines with a scope. I also have a power line filter to provide clean power for testing. I can clearly see that it reduces noise over a very wide range of frequencies that could be visible in video. Looking at the a.c. before and after inserting the filter there is clearly a difference. But when I try to follow that noise into an actual power supply to a circuit, it just is not there and there is no difference with and without the line filter. There is one case where this is not true and I can see effects of power in actual video. That is when there is a ground loop, which with the complexity of the distribution system and various equipment in the shop can be easy to create. This is easily remedied by simply making sure that everything gets a ground with no more than a few ohms resistance to the a.c. system ground, or that all of the signal grounds are tied together. This is where I believe that most people's perception of improvements in their images with line filters come from. Tying the system ground together can be done without an expensive line conditioner, however. Even a cheap surge suppressor can do the same thing.
It would be a simple matter to measure noise ratios, dropout, or other possible effects of liine noise on video. None of the claims for improvements by line filtering systems come with the data to back them up. I know that I have looked for it, and I just cannot find the effect at all, beyond ground related problems that I mentioned above. It IS TRUE that line filters work to reduce line noise. It does not appear to be true that this noise has any visible effect, however.
