Don't Get Zapped Page 5
While it might be better known for power conditioning, Richard Gray's Power Company offers many products that feature surge protection. Concerned that having passive and active surge components wired in a series can restrict the current needed by many high-powered amplifiers, RGPC uses what it calls "dual-stage" suppression that can deal with both major spikes and smaller, consistent surges.
Although the company employs MOVs, it relies mainly on a massive, 20-pound inductor to absorb surges and spikes. But RGPC products are wired in parallel with the AC line, not in the signal path between the AC outlets and the components, so the inductor places a very low resistive load in parallel with the line. This means the power is sent straight to the components, while the surge is handled via an alternate path. The inductor protects the MOV by absorbing spikes and surges before they get to a high-enough level to activate the MOV. Should the surge exceed the inductor's capability, the MOV doesn't sacrifice itself; instead, it directs the surge voltage to a fast-acting internal fuse.
Furman's Series Multi-Stage Protection Plus (SMP+) addresses some of the shortcomings of traditional MOV-based protectors by employing a variety of circuits to clamp, absorb, and dissipate transient voltages without having the device sacrifice itself. The company claims that MOVs used in a properly designed circuit will not fail.
Furman's SMP+ circuitry takes pages from both shunt- and series-mode playbooks and adds its own twist. Along with a high-voltage MOV and a high-amperage thermo-fuse varistor, SMP+ uses a tuned circuit that includes series inductors, a bridge rectifier (which converts AC to DC power), and high-voltage capacitors. This parallel circuit amounts to a critically damped low-pass filter that can absorb enough excess voltage so that the MOV is never stressed. Transient voltages are shunted to the capacitor rather than ground, avoiding ground contamination. Also, the system works in conjunction with Furman's Extreme Voltage Shutdown (EVS) circuitry, which protects against excess voltage or sustained over-voltages caused by faulty wiring by shutting down the power before it ever reaches the outlet.
Each of these approaches to surge suppression has its fans and critics, but all of the products mentioned do provide significant protection. Although MOVs continue to be most commonly used, a growing number of products combine two or more types of protection. Enthusiasts can debate the merits of the various approaches, but almost everyone agrees that if you've made a significant investment in your gear, you should certainly protect it.