OK, lets get our technologies in order. A surge protector is not a power conditioner. A power conditioner is a device that takes fluctuating and dirty power and outputs clean stable power. This is usually done by charging a large battery and inverting the DC to sine wave AC. Here are the specs for a typical commercial power conditioner:
* Voltage Regulation: +/- 3%
* Load Regulation: Typically better than +/- 3%
* Overload Capability: 125% for 10 min
* Surge Capability: 150% of rated output
* Input Operating Range: +10 to -40% (typical)
* Input Current THD: < 5%
* K-Factor: 30 or better
* Operating Temperature: 0°C to 40°C
* Common Mode Noise Attenuation: 120dB
* Transverse Mode (Line) Noise Attenuation: 70dB
* Spike Attenuation: 3000:1
* Crest Factor: 3.5:1
I have little or no experience using any power conditioning products for A/V. However, I've been employed in the industrial UPS field for 25 plus years as a designer, tech, field engineer and training instructor. So I'll offer some thoughts based on my non audio experiences.
There are line regulators that can maintain a constant voltage over a wide range input. The most common type is a ferroresonant transformer (ferro) and it is a passive device. These offer excellent isolation from surges and transients. Another type is referred to as a magnetic amp or magamp and has little in common with Bob Carver's concept. These use active circuitry to maintain voltage. Neither the ferro or magamp employ an inverter. The technology for a ferro is at least 75 years old.
There are inverters available and when coupled with a battery become a UPS. The better inverters at the low power requiremetns of A/V use pulse width modulation techniques to construct a good sine wave. They can be affected by the non linear power supplies found in most equipment resulting in distorted waveforms that could increase hum and buzz. Most UPS's sold at big box stores etc are offline types that only switch to the inverter when power fails or goes out of spec. The 12 volt DC inverters intended for camping put out a "modified sine wave" which looks more like a square wave. These work great for small TV's at tailgate parties but they're not for use in A/V.
The specs from the inverter at the top of the page indicate that it is a power factor corrected (PFC) inverter with input current THD < 5% and should be able to tolerate nonlinear loads with a crest factor up to 3.5:1. What this means is that it doesn't chop up the incoming line and won't flat top the waveform under heavy load. This one seems to me to be better than most, based on specs, and is likely expensive.
The one spec none of the manufacturers like to print is transient response which I think is as important as anything. Transient response is the deviation in output voltage due to changes in input voltage and/or load hits. I don't recall seeing any scope images of the output voltage from any of the manufacturers. Even if they did supply them I'd be skeptical of the test conditions.
From a reliability standpoint you can't beat the ferroresonat xfmr due to it's simplicity. If I was going to use anything it would probably be a ferro. I use $100 offline UPS's on each of the computers in the house and they work fine for that application. FWIW my house is fed by underground distribution to the stepdown transformer about 75 feet from my back door. Line voltage runs about 124. The switchyard is about 500 yards away.
For those people who are using some kind of line conditioning, I'd like to see oscilloscope waveforms of input and output voltages under real load. CATUION: This type of testing is not for the amateur using a scope for the first time. Grounded scope probes connected to line voltages produce burnt hands, loss of vision, ringing in the ears, electrical shock and equipment damage. A bruised ego is very possible as the scope waveforms may be disappointing.
