Mixers/Consoles Allen & Heath PA28 problem

[chrislittle]

Audio out of Allen & Heath PA28 has recently started sounding low fidelity and muffled. All sources. The exception is the headphone out. Headphones sound crisp and full fidelity. Am i looking for a bad room amp or bad output from PA28.

Thanks

 

[bishopthomas]

What do you mean by "room amp?" A power amplifier for your house PA system? My first thought when someone says "muffled" is a loss of high end speaker components. Without knowing more information, though, it's hard to say for sure. Basic troubleshooting technique says to start swapping out components until the problem goes away. Borrow a mixer/amplifier/speaker from somewhere and narrow down the suspects, one at a time, until you find the culprit. Maybe start by bypassing the mixer altogether. Connect an iPod directly to your amps and see if the problem goes away. Just make sure you start with the amp gains and iPod level all the way down.

Also, most importantly, welcome to Control Booth!

 

[chrislittle]

What do you mean by "room amp?" A power amplifier for your house PA system? My first thought when someone says "muffled" is a loss of high end speaker components. Without knowing more information, though, it's hard to say for sure. Basic troubleshooting technique says to start swapping out components until the problem goes away. Borrow a mixer/amplifier/speaker from somewhere and narrow down the suspects, one at a time, until you find the culprit. Maybe start by bypassing the mixer altogether. Connect an iPod directly to your amps and see if the problem goes away. Just make sure you start with the amp gains and iPod level all the way down.

Also, most importantly, welcome to Control Booth!

Thanks. Yeah..it's a 50 by 50 room in a church. Has about 8 jbl speakers hanging from the ceiling and a big JBL subwoofer back stage. All speakers are emitting the low-fi. The church has a guy in charge of this stuff but he has sort of a dazed look on his face when faced with questions. But he does make notes on his iPhone.

Not sure where house PA amps are. But I like your idea. I'll try to grab another mixer and see how that does.

Thanks again.

 

[FMEng]

Thanks. Yeah..it's a 50 by 50 room in a church. Has about 8 jbl speakers hanging from the ceiling and a big JBL subwoofer back stage. All speakers are emitting the low-fi. The church has a guy in charge of this stuff but he has sort of a dazed look on his face when faced with questions. But he does make notes on his iPhone.

Not sure where house PA amps are. But I like your idea. I'll try to grab another mixer and see how that does.

Thanks again.

That is an unlikely failure mode for a mixer. The most common reason for things to be muffled sounding is blown fuses or high frequency drivers in the speakers. Sustained feedback could cause that kind of damage in all the speakers at once. It could also be that someone has messed with a house EQ or processor.

 

[65535]

I'd also doubt it was the board. Also what do you mean by low-fi exactly?

it is simple enough to pull off a signal from the output of the board to "listen" in.

One really easy way is to run the mains into a stereo channel as a loop and listen to the signal via pfl on the headphones. If that sounds "off" then it is something in your board.

 

[chrislittle]

I'd also doubt it was the board. Also what do you mean by low-fi exactly?

it is simple enough to pull off a signal from the output of the board to "listen" in.

One really easy way is to run the mains into a stereo channel as a loop and listen to the signal via pfl on the headphones. If that sounds "off" then it is something in your board.

By "low-fi" I mean it sounds like highs are gone. Sounds like 80hz to about 3k maybe 5k. Sounds like AM compared to FM. Audio levels look good coming out of the board.

 

[chrislittle]

That is an unlikely failure mode for a mixer. The most common reason for things to be muffled sounding is blown fuses or high frequency drivers in the speakers. Sustained feedback could cause that kind of damage in all the speakers at once. It could also be that someone has messed with a house EQ or processor.

Thank you.

 

[museav]

Basic troubleshooting technique says to start swapping out components until the problem goes away. Borrow a mixer/amplifier/speaker from somewhere and narrow down the suspects, one at a time, until you find the culprit. Maybe start by bypassing the mixer altogether. Connect an iPod directly to your amps and see if the problem goes away. Just make sure you start with the amp gains and iPod level all the way down.

Yep, divide and conquer. Or if you are not comfortable with that or don't have the tools to do it, hire someone qualified to do it for you.

It sounds like this may also be a good time to see if you have any system documentation and if not to create it. A simple single line wiring diagram with any cable labeling, a list of equipment models and serial numbers and so on can go a long way in helping troubleshoot problems and documenting this information now can keep you from having to find it every time there is any problem with or desired change to the system. It will also help others be able to more effectively help you if you can provide them such information.

 

[FMEng]

Another thought....

The speakers could be bi-amplified. The low speakers driven by different amplifiers than the high drivers. In that case, there would be an active crossover in the amp rack. It could be a failure or mis-adjustment there.

Museav is right on. Make yourself a block diagram of the system before you touch anything, otherwise you could easily make things worse. Document every setting before you change it, so you can restore it. If you don't fully understand it, it might be time to bring in the original installer to take a look.