Broke our mixer?


PDA

View Full Version : Broke our mixer?


warrenduane
12-20-2009, 09:07 AM
We've got a 1000w powered mixer that I've tested with one speaker previously (worked fine), and tried hooking it up to our PA system today, 2 500w speakers and 2 200 watt monitors, all 8 ohms. All we did was daisy chain each pair of speakers and plug them into the outputs, and plug all our mics in. Needless to say, something went wrong. Whenever you turn the mixer on now, the light comes on and it powers up for a second, but just turns off instantly. If you try doing it again immediately after, nothing happens. You have to then leave it a couple of minutes before it will power on for a second, then turn off. Is it screwed?

SomeoneYouKnew
12-20-2009, 10:01 AM
solid-state amps are perfectly happy with no speakers connected. try turning the volume to zero on the master, unplug all the speakers, and turn it on.

If the power light stays on, it's probably a short in one of the cables or speakers that's causing the mixers protection circuit to shut down.

If the power light turns off after a second, like it does now, it's screwed.

warrenduane
12-20-2009, 10:18 AM
Yer, it just goes off. What would've broken it?

isabiggles
12-20-2009, 10:19 AM
Hang on...

does the mixer work without all this mumbo jumbo with it or is it doing this without all of it? I'd take it to a pro or at least someone who knows what he's talking about in real life because it's not exactly easy for someone to diagnose what the problem is over the internet. Are you sure that it's absolutely the fault of these speakers or might something else have gone wrong.

I mean, for example, I was recording and suddenly my microphone stopped picking up sound. Naturally, I assumed that it was the microphone that was broken but when I realised that it wasn't that I thought it was Cubase which had the problem. Anyway, turned out my lead was broken.

Just check all the little tiny things to make sure that they're still working. Process of elimination is boring as hell but it's important (unless you take it to a pro).

warrenduane
12-20-2009, 10:37 AM
It is doing it with nothing connected.

SomeoneYouKnew
12-20-2009, 10:40 AM
It is doing it with nothing connected.then the problem is internal. You've done all you can.
If it's under warranty, try to exchange. If not, take it to a repair shop.

:cheers:

axemanchris
12-20-2009, 11:50 AM
So I guess the next question is "what happened between the time it worked and the time it died?" I mean, you'd *really* hate to get it fixed, only to kill it again.

Go through this with us, please.

You've got an amp = 1000W. Great. What is the load at the outputs? Is it switchable? What position was the switch in?

You have two 500W mains and two 200W monitors. Paired with a 1000W amp, doesn't sound like the wattage is a problem. (mind you, my knowledge of this stuff can be a little sketchy)

Now, all four of these speakers are rated at 8 Ohms?

You say "daisy-chained" but how? You didn't daisy-chain all four of them together from one output, did you?

Did you drive one output for the monitors (the two of them daisy-chained together)and one output for the mains (also daisy-chained together)? That's pretty typical.

Are there any switches on the speakers for impedance loading?

Do (did) you have any leads plugged in to a series jack when they should have been plugged in parallel?

DID YOU USE SPEAKER LEADS? You can really screw up an amp by hooking it up to a speaker with a guitar patch cable.

CT

isabiggles
12-20-2009, 11:50 AM
then the problem is internal. You've done all you can.
If it's under warranty, try to exchange. If not, take it to a repair shop.

:cheers:

+1

Or you can fiddle with it and see if it's something simple but best thing would be to take it in.

SomeoneYouKnew
12-20-2009, 01:53 PM
So I guess the next question is "what happened between the time it worked and the time it died?" I mean, you'd *really* hate to get it fixed, only to kill it again.Good call.

TS, read that post and evaluate your situation carefully.

take_it_t
12-20-2009, 02:22 PM
Saying the speakers are daisy chained, isn't really that helpful, since all that really describes is the layout. I still can't tell whether you have your speakers wired up in series or parallel.

Also would be good to know how many channels the amplifier is.

warrenduane
12-20-2009, 06:12 PM
DID YOU USE SPEAKER LEADS? You can really screw up an amp by hooking it up to a speaker with a guitar patch cable.

I think we used one somewhere, yes. I didn't realise there was any difference. Is it fixable?

warrenduane
12-21-2009, 07:30 AM
So can anyone help? Is the fact that it turns on temporarily a good sign? Could it be as simple as replacing the power unit or something?

SomeoneYouKnew
12-21-2009, 08:29 AM
So can anyone help? Is the fact that it turns on temporarily a good sign? Could it be as simple as replacing the power unit or something?It sound bad to me. I'm only guessing, but it sounds like maybe some of the output transistors have failed. Shorted internally, they're causing too much current to flow from the power supply. Sensing this, the protection circuits are shutting the whole thing down. This is not something you as a user can deal with. It's a job for a pro.


What you can and should do is check everything you plan to connect to this. A shorted mic cable won't damage the mixer. But a shorted speaker cable or too low of a speaker impedance could.

Make sure you have proper cables. An instrument cable being used as a speaker cable is dangerous. The inner conductor is small and can't handle the current without becoming hot. The heat can melt the insulation between the inner conductor and the shield. If it shorts, this can damage the amp inside your mixer.

When you chain speakers together, usually the connections are parallel. Parallel two 8 ohm speakers and the impedance is now 4 ohms. If the amp was designed for 8 ohm, this can lead to failure. Connect two 4 ohm speaker systems in parallel (2 ohms) and connect that to an amp designed for 8 ohms and you'll likely experience failure very quickly.

Some amps are designed with sensing/protection circuits on the output. Others aren't those that don't have built-in protection can fail requiring expensive repairs.



When all else fails, read the manufacturer's instructions.

warrenduane
12-21-2009, 10:53 AM
Okay, so here's a picture. I think we are in series, no? I think that an instrument cable was being used as the 1/4 inch connections between the main speakers.

It was only on for one second and it didn't work... is that enough time for the instrument cable to short whatever component?

http://img63.imageshack.us/img63/7695/pasetup.gif (http://img63.imageshack.us/i/pasetup.gif/)

take_it_t
12-21-2009, 11:50 AM
I still can't tell if it's series or parallel though, but from the looks of things it's most likely parallel, which means the combined resistance of your 8 ohm speakers would become 4ohm's. Subsequently, wiring them in series would give you 16 ohms. So if your amp's output is rated for 8ohms, neither situation will work, and you need to use a different wiring scheme, to achieve an 8ohm load. But that's all based on assumptions, so before I can explain how to do that, theres a few things we should clear up.

Now based on your diagram, I am assuming the amp is 2 channel. You said the system works when you have only one speaker, was this speaker hooked up with the amp set to mono ouput? Most amps will have a switch to change the output mode on the back, so please confirm that the amp is set to stereo mode for the setup in your diagram. If that's the case, what is the impedance (ohmage) of each channel when the amp is in stereo? That information should be printed on the back of the amp itself.

Phil Starr
12-23-2009, 03:12 PM
It looks to me as if you have run all four speakers in parallel which means you presented your amp with a 2 ohm load as has been said. This could well have blown the output and/or driver transistors though there may be an internal fuse gone somewhere which would at least be quick and cheap to fix.

It could also be coincidence though so don't jump to conclusions.

Check that you have one working speaker with another amp. Using the same speaker lead and just that speaker check this amp. try changing the mains lead if it doesn't work still. If you still get no joy then it has to be the mixer amp but at least you know.
Instrument leads have a higher capacitance than speaker leads and this could lead a poorly designed amp to become unstable but this is unusual so I doubt that caused your problem.

If you go into gear maintenance in the columns there is an article on fixing intermittent faults and another on matching speakers and amps which might help you work out what is going on. But you probably have to go to the repair shop if it isn't a problem with leads.

Sorry.