This is a very confusing area of product and Ive been involved with a few manufacturers who build things like this. What I have learned is that the description "power conditioners" is used for a very wide mix of different products that do different things. The manufacturer info is so poor it's hard for us as consumers to work though what does vs what does it NOT do. But do your research and I think it pays off. So the different devices that are called power conditioners:
Transformer based power conditioners: These are the real power conditioners and they need a massive transformer to do their job. What they do is isolate inside power from outside power and the quality of there transformer and the size matter. This is mainly used to build a wall between inside and outside, preventing noise from getting into internal AC lines even if it's present on outside lines. This what studios and other [especially medical] folks use to get the AC circuits quiet. This is also the type of conditioner that makes gear sound better, video look better etc. The only time they appear not to work is when you have noise being injected into your lines by internal sources, such a motors or digital/switching power supplies or dimmers inside on the same power/circuits as the audio devices. Because they are transformers, they have a limit to how much power they can supply and you buy them based on how much power you need. This is also a bit confusing as you need to know what the actual power draw from the gear you are hooking up to it is. That can be a challenge to determine from gear manufacturers spec sheets and we often we are left to guess. This is where dealing with an experienced power conditioner company helps as they can advise you. You can sometimes spot a transformer based conditioner by weight. If the conditioner is a small one rack unit and costs less that $1000 and weights 3 lbs its likely not a transformer based conditioner. There are some small cube like Tripp Lite conditioners like this and have small power draws available (600W) for one piece of gear like one power amp or a TV.
Power Regenerators: Their purpose is to completely separate inside from outside power as fresh power is regenerated inside the unit. IF you start over with new power there is no noise. This idea does work but it not common in industrial application which is a clue. They are not fool proof and can also be a problem as I know of one manufacturer of recording consoles that had several consoles power supplies blow up on this type of system. I don't know much about the good vs bad situations on these regenerators so do your own research. They are controversial, I am aware of some who love them and some who hate them.
Voltage Regulators: These are devices that just make sure the voltage stays stable under low or high conditions. This is not a transformer, not a line conditioner but additional parts built into the AC line to create this voltage regulation feature. Its can be used with a transformer, a surge system or stand alone. Today, many units have MOV's built in to the power supply that prevent the unit from operating in an over (too high) voltage condition.
UPS: Uninterruptible power supplies: this a device that can supply power to its outlets via an internal battery for some period of time if the incoming power fails. They may or may not have any other features like Surge protection, Line Regulation or RF filtering etc. They are not conditioners.
Surge protection: Depending on how likely you are to suffer from lightening storms this may be very important feature. Some of the surge protection is so small or slow it doesn't really protect anything, some of it is very good. Alone these surge devices don't condition anything or improve anything. They can prevent damage from spikes which can happen in storms or from other gear on the same circuit failing and putting a big spike on the line. If I lived in a area with lightening I'd want one as I remember a TV blowing up at my grandparents farmhouse in so Illinois during an electrical storm (and they had lightening rods).
RF/EMI filters: these are devices inside the unit that filter out frequencies that are associated with RFI or EMI that are riding on the AC. Just like EQ, its reduces the level of some of these RFI and EMI noises. It's a real thing and happens often in places like New York or if you live near a radio tower or other strong RF source. Im not sure if you've experienced your cell phone making noise into your computer but this is RF noise. RF and EMI can also happen in the middle of nowhere where the power quality is poor, like being a long way away from the originating power source on an old system (old electrical grid). I would guess noise is present in electrical lines on some of these rural farms. EMI/RF suppression It's also a bit of crap shoot as the just like EQ on audio, the RF/EMI may not filter out the exact frequencies that are causing you the problem. These are usually added to transformer based line conditioners on some of the outlets but not all. Digital switching supplies are notorious for putting noise on the line and even if you separate inside from outside if you have a lot of digital supplies on the inside the noise can get passed around among devices on those same lines. I am unaware of a 100% fool proof EMI/RF solution.
It's still possible to have RF get into gear with one of these RF/EMI filters on the AC when the RF/EMI is so strong it injects itself directly into the audio boards of the unit. To prevent this you need shielding and this can be difficult to accomplish. It its basically build an RF shield around the affected unit using copper tape or other method and then draining away this RF from the audio lines. Manufacturers who have to repair or build and test RF units use a cage called Faraday cage to isolate the space inside from all RF so they can work in an interference free zone.
We see problems of RF in pro studios sometimes with gear that works perfectly 99% of the locations on earth and then gets into one location in a high RF area and there is a problem with a radio station or other noise being heard in the audio of a particular piece of gear. EMI is often something that appears from a large motor on the line like an old refrigerator. This does not mean the gear is defective. Manufacturers don't automatically build extensive RF/EMI filtering or shielded supplies or shield audio boards as it's expensive and applies to such a small number of cases it wouldn't be a benefit to all customers.
So if I follow some of the posts earlier in this thread I find all kinds of different devices that are called line conditioners that are actually voltage regulators, RF filters, surge protectors or other variants with no uniformity as to what is being called a power conditioner.
The only ones I have seen/heard actually work to reduce noise, improve sound/video and isolate inside from outside are the transformer type and these are too large to be a power strip. Furman does make one high end rack unit like this, Tripp Lite makes a number of them, Equitech is what the studios use, etc. I see none of these exotic high end brands that are sold in audiophile land (that promise improved audio) show up in studios where low noise is a critical feature of the reason you work in a studio to start with. One would think if there was consensus, or something that universally worked, you'd see it everywhere. The only real consensus I see is the transformer type conditioner. So, Buyer Beware.
The caveat to all this is that one can hear differences in AC cables, connectors etc and I have not seen any consensus on the explanation for this other than marketing speak. George Cardas explained it once to me and his was the only explanation I ever heard that made sense. He was from the power industry, where they are moving high voltage across states on those giant lines that stretch on for miles.
Brad
