So a funny thing happened on the way to the website…Just as I was getting ready to post the last post of 2016, I got a notice that my security certificate was invalid. Knowing that I needed to touch up my domain config and enable SSL, I decided to click those buttons. What could possibly go wrong? Well, after knocking CTA out for a few days, we’re back. And now it’s 2017! But this is still a good post, so here it is the last post of 2016, and the first post of 2017…
As I was thinking of topics to wrap up the year, I wanted something powerful, something electrifying, something high-voltage. Then it occurred to me that I’ve not done a post on technical power. And since pretty much everything we use every weekend runs on power, it’s kind of an important topic. Power is also something often overlooked during a build or remodel. Many of the problems we have with sound and video can be traced back to bad power. There’s actually a lot to this subject, and I’m not sure I can cover it all in one post. But let’s see how far we get.
Go To Ground
At some point, all power ends up at ground. After it has done its job, power goes to ground. And that’s where problems tend to crop up. I’ve seen many a church wired up with the stage power coming off one panel and the tech booth power coming from another. Electricians do that because it may be easier for them, and they really don’t understand what we do. The problem comes in when there is a different ground potential on those two circuits and we connect them together with audio wiring (or video wiring, for that matter).
How do we connect them together? Let’s say your amps are on the stage panel, while your mixer is on the tech booth panel. Connect your mixer to the amps with a balanced audio cable. The ground (shield) on said cable connects to the chassis grounds on both the mixer and the amp. Guess where those chassis grounds connect to? The ground pin in the outlet.
Now, let’s say we have 3-4 volts on the ground leg of the stage panel and 0 on the tech booth panel. That little voltage will flow over the shield and induce hum into your signal.
It is for this reason that when we specify tech power, we always specify dedicated, isolated ground panels. An isolated ground isolates the neutral bus from the ground bus. I won’t go into technical details here, but it goes a long way to prevent what I just described. We also always specify this IG (isolated ground) power for the audio and video equipment. Lighting gets put on its own panel. In a pinch, if budget is tight and the lighting rig is small and LED, we can pull lighting power from a general-use panel. But never from the AV panel.
We also like to isolate the incoming power from the power company. I’m a big fan of using isolation transformers in front of my AV, isolated ground panels. This de-couples the tech power from the power company power and cleans it up a lot. While an Iso transformer can cost thousands to tens of thousands of dollars, it’s really good insurance. There’s nothing worse than hum or bitrate errors in your brand-new $300,000 AV system because you tried to save $7,500 on a transformer.
It’s important to segregate your power usage in the booth and on stage. In all the venues we design, I specify AV circuits and lighting circuits in the tech booth and on stage. The AV circuits should be clearly labeled (orange outlets are good) as IG and only AV gear gets plugged in there. Any floor-based lighting fixtures (along with lighting consoles and distro gear) get plugged into the lighting circuits.
We will often use either relay panels or a motorized breaker panel for turning the system on and off. We like Lyntec, but there are other brands available. Sequencing allows you to press “On” and have the entire system power up in the right order (mixer and stage racks before amps). It goes back off in the opposite order. It’s also important to have both sequenced and non-sequenced AV circuits in the tech booth. Often, you will want to leave computers or other devices like UPS’s on all the time, and you don’t want them shutting down with the sequence. Speaking of UPS…
Split Your Power Supplies
It’s a good idea to put your critical gear on a UPS (uninterruptible power supply). This battery backup will cover you forfew minutes in the event of a short power outage or blip, and will give you time to shut down gracefully for longer outages. Mixing sequencing and UPS can get tricky, however. If you put your mixer on a UPS, you can’t put it on the sequence. It has to be manually powered up and down.
Also, if your console—or any other piece of gear—has dual power supplies, don’t put them both on a UPS! If the UPS dies mid-service, and I’ve seen and heard of it happening more than once, you lose your console. Plug one power supply into the UPS so if you lose house power, the console stays up. If you lose the UPS, the console stays up.
If you live in an area where storms are prevalent or your power isn’t very stable, surge protection is very valuable. Lyntec (and others) can install transient surge protection in the panels, and while not inexpensive, it might just save your $10,000 projector. We always specify TSP for our AV circuits, and if budget permits, lighting circuits as well. You can also do local surge protection if the budget doesn’t allow for panel-based TSP, though it may not be as effective.
A Balancing Act
Budgeting for all this power is a bit of a balancing act. Doing power correctly for a mid-sized AV system can easily add $25,000-30,000 worth of electrical gear to a project. If your PA/Mixer upgrade is a pair of self-powered $1,200/ea. speakers and an X32, that’s probably overkill. But if you’re spending a couple hundred thousand dollars on the system, it’s money well-spent. The key is getting it designed properly. I’ve seen some designs that are so grossly over-done that the church probably wasted $40,000 on power gear they’ll never use. On the other hand, going to small will limit you in the future. You have to know the long-term plans for the room. I like to have at about a half-dozen empty circuits in the panel board, unless the building will be greatly expanded. Only then are more appropriate. Then again, I’m working with a church right now doing a PA upgrade, and we need 6 new circuits for the amps, DSP and wireless rack. Having open space is a good idea.
There’s probably much more I can say about power, but I’ll stop for now. Being that this is the last post of 2016, I want to thank you for reading this year—and in years past—and hope you’ll stick around for 2017. Next year, ChurchTechArts will be 10 years old, something I never envisioned when I started. Thanks to those that have stuck around from the beginning, and to all the new readers that just joined. I have some news for 2017 that will hopefully generate some excitement, but we’ll wait until next week for that. Happy New Year!