Power Conditioner AC Power Conditioner for Home Theater

What a power conditioner is

"Power conditioner" has no standard definition. Headfonics notes that the label covers everything from pulse protectors and automatic voltage regulators to uninterruptible supplies that synthesize a sine wave, and advises checking the specification first. Wikipedia lists the common functions: surge protection, noise suppression rated in decibels, isolation of each outlet from the others to cut cross-talk, and in some units minimal voltage regulation. The useful question is which of those functions a given model actually has, and what number backs each one.

How the functions work, with real specs

Furman's published specifications show what a high-end home-theater unit claims. The Elite-20 PF lists series multi-stage surge protection with 188 V peak clamping at a 6,000 V / 3,000 A input, EMI/RFI attenuation above 40 dB from 5 kHz to 100 kHz and above 80 dB from 100 kHz to 1 GHz, an extreme voltage shutdown above 137 VAC, and a combined output of 16 to 20 A with 4.5 A of reserve on the four power-amp outlets. The SPR-20 adds regulation: a 120 VAC output held to about +/- 1.0 V typical across a 113 to 126 VAC input, a shutdown at 135 +/- 5 VAC, and 19 A continuous at 114 VAC.

Put in percentages, the SPR-20's regulation window spans 94% to 105% of a 120 V nominal supply (113/120 and 126/120). Wikipedia defines a swell as 10 to 80% above nominal and a sag as 10 to 90% below, with undervoltage meaning below 90% for more than a minute, which is 108 V on a 120 V circuit. The spec promises regulation only inside the 113 to 126 V window, so a long brownout at 105 V is outside it.

Series designs carry the whole load. The Tri-Service Electrical Working Group notes that series surge protectors must carry the circuit's full load current, that losing one means losing power to everything downstream, and that they are used mostly on individual loads and usually add filtering. Note too that 188 V is below 330 V, the lowest UL 1449 voltage protection rating, so it is a manufacturer clamping figure rather than a UL VPR; see surge protection ratings.

What the measurements show

Filtering is measurable at the mains and often invisible at the speakers. An Audio Science Review forum thread on a conditioner reports members agreeing that such filters usually do something measurable to the power line, but that at the audio outputs it usually makes no difference, and that ASR's method is to measure what the conditioner does to the audio signal. The same thread notes that the Trifield line meter used in YouTube demos reads noise from 10 kHz to 10 MHz, a band that is largely above hearing.

Where a device is sensitive, the effect can be real. Murata, a component maker, reports that adding its power-line filters to a Class D amplifier improved conducted higher harmonics of the switching frequency by over 20 dB and improved THD+N. That is a filter inside the design path, not a strip at the wall, and it shows the benefit tracks the equipment, not the brand. For a modern AVR with a regulated switch-mode or linear supply, the strip's contribution is smaller. Headfonics frames the test fairly: compare noise at the analog output with and without the conditioner, and if there is no visible difference, use it as extra surge protection.

Current is the cost. A Denon AVR-X3900H is listed at 660 W power consumption, about 5.5 A at 120 V (660 / 120), well inside a 15 A circuit, but a series conditioner is another stage that must pass the amplifier's peak current. Furman lists 4.5 A of reserve on the Elite-20 PF's amp outlets for that reason.

Power conditioner vs surge protector vs UPS

A plain surge protector clamps spikes and does little else. A conditioner adds filtering and, on some models, regulation and shutdown. A UPS adds a battery. The Tri-Service group says to require a UL 1449 listing, and that response time and joule ratings are secondary: response time matters little because let-through voltage is what counts, and the joule rating is not an important performance attribute for a listed device. So a conditioner is not clearly a better surge protector than a listed strip with a 330 V or 400 V VPR. What the money buys is the filtering, outlet isolation, and the shutdown feature.

Who benefits

Buy one for a defined problem: a hum that goes away when a conditioner with an isolation transformer is inserted (Headfonics notes an isolation transformer can break ground loops; see ground loop hum), a region with documented over-voltage events that trip an extreme-voltage shutdown, or equipment worth protecting with a series stage. Do not buy one expecting a sharper picture or tighter bass; the ASR forum position is that the audio output does not change. For most rooms, a UL 1449 listed surge strip covers the failure that actually destroys gear; surge protection ratings covers the Type 1, 2, and 3 placement options. See the AVR buying guide and the power draw tool.

Common confusions

A power conditioner is not a power amplifier source or a "clean power" generator. Unless it synthesizes its own output, the AC that exits is the AC that entered, minus some noise. Headfonics adds that a conditioner does not guarantee a sine wave at its outlets. Also, a high EMI number is not a high audio benefit: the specified 80 dB is attenuation of line noise in one test configuration, not an improvement at the speaker terminals.