This week's article is going to center around PA system failures, how to locate the problem and how best to fix it on the spot. But keep in mind that these techniques can be applied to any sound system (namely guitar and bass rigs).
The first thing to do is not panic. When you freak out, you rush and usually overlook the simple things. As long as there hasn't been a loud "bang" and smoke isn't pouring out of your amp rack, there's a very good chance that you're going to be able to recover. You might have somewhat reduced capacity (channels, power, etc), but you'll probably be able to play the show.
The trick to troubleshooting a problem...divide and conquer. Don't try to look at your entire system at once. Instead, think about your system in blocks, with the signal starting at the microphone and ending at the speakers.
It Ain't Got No Gas In It...
Before you go ripping things apart, is everything that needs to be plugged in actually connected to a power source? Yeah, I know...seems overly simple. But I've been tripped up by this, and have actually seen the drive rack of an arena sized system (with 16,000 people in the audience) ripped apart only to find out that a breaker was inadvertently shut off.
Most gear has some kind of light on it to indicate power, but not always. I'm the proud owner of a few EV powered subwoofers that have no indicators on them at all. I had one that wasn't functioning at a show, and started swapping the signal cables to it. Come to find out that the IEC power connector was partially out of the socket, and I hadn't seen that (black connector, black speaker, dark club). Pushing that back in solved the problem. By the way, have I ever ranted about how much I hate IEC connectors? On the next performance break, those are getting retrofitted to Neutrik Powercon connectors.
Get The Easy Stuff Out Of The Way
It's not dumb stuff...it's only dumb if you blow past it. Every connection point in a system is a potential location for either an error or failure. I did some quick addition, and with The Rhythm Dawgs sound system, there are about 400 total connection points for audio. If you just consider 1 microphone through to the speakers, there's 32 total points (if you include the monitors). And all it takes is one to go down.
So make sure the easy solutions are checked. Are the mics actually plugged in (and if you're using sub-snakes, do forget to check there.
How Bad Is It?
Is the whole PA not working, or just a single mic? If the entire PA is down, then think about it logically. Which is the more plausible situation:
- All the channels on the board went down at the same time
- All of my mics and/or cables are bad
- I don't have the crossover or amp turned on
I gotta go with the last one. Unless you've had an electrical event (surge, brown-out, etc) then you usually just have a single fault to deal with. If the whole system isn't working, then start at the speakers and work back down the speaker cables to the amps, then the crossover, and then back to the board.
If you can hear a hiss coming out of the horns on the PA, then you can assume that the power amps are working.
Remember, think single-fault. Ask yourself "what one piece of equipment can take out the whole PA?".
Of course, there have been those times when I've found a bum mic, a bad cord, and a failed compressor in the same night. But those showed up as 3 different channels that didn't work.
Get The Easy Stuff Out Of The Way
It's not dumb stuff...it's only dumb if you blow past it. Every connection point in a system is a potential location for either an error or failure. I did some quick addition, and with The Rhythm Dawgs sound system, there are about 400 total connection points for audio. If you just consider 1 microphone through to the speakers, there's 32 total points (if you include the monitors). And all it takes is one to go down.
So make sure the easy solutions are checked. Are the mics actually plugged in (and if you're using sub-snakes, do forget to check there.
How Bad Is It?
Is the whole PA not working, or just a single mic? If the entire PA is down, then think about it logically. Which is the more plausible situation:
- All the channels on the board went down at the same time
- All of my mics and/or cables are bad
- I don't have the crossover or amp turned on
I gotta go with the last one. Unless you've had an electrical event (surge, brown-out, etc) then you usually just have a single fault to deal with. If the whole system isn't working, then start at the speakers and work back down the speaker cables to the amps, then the crossover, and then back to the board.
If you can hear a hiss coming out of the horns on the PA, then you can assume that the power amps are working.
Remember, think single-fault. Ask yourself "what one piece of equipment can take out the whole PA?".
Of course, there have been those times when I've found a bum mic, a bad cord, and a failed compressor in the same night. But those showed up as 3 different channels that didn't work.
Look At All The Pretty Lights...
Yeah, all those sexy LEDs on your equipment aren't just there for the bling factor...they can actually tell you what's going on (and through) your gear.
On most mixers, each channel has an overload indicator to assist you in setting up the gain structure. Then, there are likely meters on the sub groups and mains.
So, start with the channel strip and make sure you're at least getting to there.
If you don't have anything going on here, you've got one of these issues to deal with:
- The channel on the board is bad...try another
- The cable between the mic and the board is bad...swap it out
- The mic itself is bad...try another mic
- The mic was plugged into the wrong channel...follow and check the wiring
Assuming things are hooked up correctly, then the cable is usually the first suspect.
If you've got signal to the channel strip, turn up the channel fader, the subgroups, and the main fader.
Still nothing? Is the channel assigned to an output? This is an easy place to get tripped up. Unless you tell the channel what to output to...it's going nowhere (except the monitor bus). When I'm troubleshooting a channel problem, I like to assign the channel directly to the main output bus (usually marked L-R on the assign switches). Now, you should have some indication of signal on the output meters.
If the channel works to the main outputs, but not the subgroups, then make sure that the subgroups are assigned to an output. In this case, each sub can be assigned to left, right, or both. And again, if nothing is selected there's nowhere for the signal to go.
Any failures after the console will tend to take out the entire system. That is, nothing will be able to get through.
We're Out Of Time
If you're lucky, you find your issues when you set up and sound check. However, there's a corollary to Murphy's Law that states the likelihood of a system failure 5 minutes before showtime is directly proportional to the number of people waiting for you to start.
So, how do you handle a last minute failure quickly? Like I said earlier, don't panic...nobody has died because a show started late. (If that was the case, Guns 'n Roses would have killed several million people in the 80's).
Is it a system failure or a channel failure? Just remember that:
- For a system failure, start at the speakers and work back to the amp rack and mixer.
- For a channel failure, start at the source (mic, DI, etc), and work to the mixer.
If you've got a fairly complex system, do yourself a favor sometime and sketch out the signal flow. It doesn't have to be a work of art, but included each piece of gear from the mixer input to the speakers. Here's one I did in about 5 minutes:
It ain't pretty, but if I'm tired / drunk / whatever...this will jog my memory. Make your own chart, put it in a plastic sheet protector, and tape it in your amp rack. You'll thank yourself later.
In this article we had a brief mention of subgroups on a mixer. I find that, after gain structure, this is a fairly misunderstood feature. Subgroups used to be a feature that you only found on large high channel count boards...now their everywhere.
Next week we'll talk about strategies on how best to utilize subgroups to make your mixing easier. We'll also be talking about the benefits of group compression (which I'm loving on my new StudioLive 24.4.2), so if you've forgotten most of it, re-read my article "Putting The Squeeze On" to review compression basics.
Until then, keep the metersout of the red moving!
Ken
Ken Carver has been a musician and performer since the early 70's, and involved with live music production since the mid 70's. He worked for 15 years as a broadcast engineer, building numerous studios and transmitter sites around Texas. He's also worked in Critical Care Communications for the medical industry, R&D for an automated lighting manufacturer, and owned Project Lighting & Sound in the 80's. He currently heads up an R&D Hardware Technician Team at National Instruments in Austin, and still performs on the weekends in the Central Texas area. You can reach Ken at itsjustlogistics@gmail.com
If you've got signal to the channel strip, turn up the channel fader, the subgroups, and the main fader.
Still nothing? Is the channel assigned to an output? This is an easy place to get tripped up. Unless you tell the channel what to output to...it's going nowhere (except the monitor bus). When I'm troubleshooting a channel problem, I like to assign the channel directly to the main output bus (usually marked L-R on the assign switches). Now, you should have some indication of signal on the output meters.
If the channel works to the main outputs, but not the subgroups, then make sure that the subgroups are assigned to an output. In this case, each sub can be assigned to left, right, or both. And again, if nothing is selected there's nowhere for the signal to go.
Any failures after the console will tend to take out the entire system. That is, nothing will be able to get through.
We're Out Of Time
If you're lucky, you find your issues when you set up and sound check. However, there's a corollary to Murphy's Law that states the likelihood of a system failure 5 minutes before showtime is directly proportional to the number of people waiting for you to start.
So, how do you handle a last minute failure quickly? Like I said earlier, don't panic...nobody has died because a show started late. (If that was the case, Guns 'n Roses would have killed several million people in the 80's).
Is it a system failure or a channel failure? Just remember that:
- For a system failure, start at the speakers and work back to the amp rack and mixer.
- For a channel failure, start at the source (mic, DI, etc), and work to the mixer.
If you've got a fairly complex system, do yourself a favor sometime and sketch out the signal flow. It doesn't have to be a work of art, but included each piece of gear from the mixer input to the speakers. Here's one I did in about 5 minutes:
It ain't pretty, but if I'm tired / drunk / whatever...this will jog my memory. Make your own chart, put it in a plastic sheet protector, and tape it in your amp rack. You'll thank yourself later.
In this article we had a brief mention of subgroups on a mixer. I find that, after gain structure, this is a fairly misunderstood feature. Subgroups used to be a feature that you only found on large high channel count boards...now their everywhere.
Next week we'll talk about strategies on how best to utilize subgroups to make your mixing easier. We'll also be talking about the benefits of group compression (which I'm loving on my new StudioLive 24.4.2), so if you've forgotten most of it, re-read my article "Putting The Squeeze On" to review compression basics.
Until then, keep the meters
Ken
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