Monday, February 11, 2013

Power Conditioners

This post is part of a series on eliminating noise from audio systems. Click Here to see them all.

A lot of people experiencing noise in their audio think to go for a power conditioner first. Unfortunately it's often money wasted as power conditioners only address a few specific issues. They don't do a thing to fight the biggest cause of hum on the stage or in the studio. Ground loops. We'll cover that in the next post. Right now it's down to what a power conditioner can actually do for you.

Your garden variety rack mount power conditioner is basically just a power strip with rack ears. There's a couple features that are usually better implemented than what you'll find in the more expensive pieces of office equipment. Rack gear might have a voltage meter or a nice set of lights but that's just window dressing. A fuse or more likely a circuit breaker or thermal overload will round out the basic features.

What actually counts is filtering and the ability to deal with power surges. The filtering on most units is a simple low pass filter on the hot and neutral connectors right after they come in to the unit. That's right, simple audio technology to filter harmonics from the power. It's a passive filter with all the limitations that any other passive filter will have. Some are better than others. Compared to other issues you can have though, harmonics in the power can be pretty hard to hear in finished audio unless you have a severe issue.

The only other technology is the surge protection. This is usually just a couple MOVs across the terminals of the outlets. An MOV is a metal oxide varistor. It's a device who's internal resistance increases as the voltage across it increases. When a big surge comes down the line the resistance skyrockets in the MOVs, causing them to absorb the spike and produce heat. Many are single use depending on the severity of the spike so there are a lot of racks out there that are basically unprotected after they do their job once. One feature that office surge protectors have is a circuit that indicates when protection is present. Once the MOVs give up the ghost the light goes off and you know it's time to replace.

Some more advanced units will have over and under voltage protection. This is usually some sort of indication when the power slides out of the ideal range and full shutdown if it drifts further. These days voltage conditions are less of an issue as switch mode power supplies can accept quite a wide range of input voltages and still deliver clean, stable DC to the gear.

A UPS (uninterruptible power supply) can do a little more for you, although basic models might do more harm than good. These devices have internal battery packs that run an inverter when mains power is interrupted. A cheap inverter is doing nothing more than passing a 60 Hz square wave. This can really do a number on motors and electronics unless they're specifically rated for inverter duty. Better inverters will supply a smoother sine wave. This technology is constantly coming down in price and even relatively inexpensive inverters can be found with this feature.

The best of the best though are dual conversion setups. This is like a UPS but runs continuously. AC power comes in and is rectified to DC which charges the battery bank, but also continuously runs a very good inverter. Many produce better power than you can get from the utility company and they do it continuously, not just during power outages. These are commonly seen in phone and network rooms where sensitive equipment has to run 24/7. They're expensive though so this type of gear isn't often seen outside of the ritziest studios.

So that's the low down on power conditioners Brethren of the Knob and fader. Check back tomorrow for the skinny on eliminating the rest of the hum from your rig or studio.

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