Surge Suppressor Basics

Protection of audio equipment from AC power anomalies using surge suppressors has been widely discussed and, because of its importance, is worth reviewing….

Surge/transient suppression is basically accomplished by the use of parallel-mode or series-mode devices. Parallel-mode suppressors use metal-oxide varistors (MOVs) that are effectively in parallel with the incoming AC supply and the connected equipment. They are considered “sacrificial” because they are willing to give their lives to save your equipment. In doing so, however, they usually become damaged and are no longer capable of protecting equipment.

Series-mode suppressors came on the scene and their claim to fame was superior surge protection with very low “let-thru” voltage and the ability to withstand numerous 6,000V/3,000A “hits” with NO damage or degradation. The device that provides this protection is a reactor (inductor) in series with the AC line supply that opposes changes in incoming current or voltage. Unfortunately, the reactor also results in a higher source impedance and connected equipment (power amps, in particular) can become current-starved during demanding musical passages. The audible result is reduced dynamics and bass impact. To counteract this, some companies use capacitor “banks” to satisfy dynamic current demands. Such capability does not come cheap and to use one example, the Audioquest Niagra 3000 has a retail price of $3,000.

The approach used by most audiophiles is to simply run all source components through the series-mode suppressor and to plug the power amp (or integrated amp) directly into the wall outlet. This works well since the power consumption of most source components is very low with a near-constant current draw.This setup, of course, leaves the power amp unprotected.

The solution to that problem, as mentioned, can get expensive. It may well be, however, that the current demand of some amps are low enough that plugging them into the series-mode suppressor has no (or minimal) effect on sound quality. The only way to determine that is to try it. For some, a slight degradation in sound is a worthwhile tradeoff for the protection offered.

I use furman Elite 20 PFI, that uses similar scheme. Big inductor in series followed by big capacitor (parallel). They claim it can provide 55A peak current. Most of linear power supplies draw current in short pulses of big amplitude and this arrangement stores required energy. It slows down (flattens) overvoltage spikes, but also filters out (flattens) load current pulses, making them appear to mains, more like resistive load, hence PFi in name (Power Factor). In addition it has circuit breaker and non-sacrificial protection (possibly SCR), that is triggered not only in overvoltage, but also in undervoltage condition. It resets itself when voltage comes back to normal. I paid $600 for used one, but 15A version (Elite 15 PFi) is likey less.

@kijanki - Furman makes quality stuff and the Elite is a good example with many happy owners.