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LordNor 15th May 2012 07:13 PM

System makes bad chirp sound, need help
I have a sound system in a coffee shop/dance hall (for teenagers in recovery). The system is a windows based computer running iTunes plugged into a NuMark Dm1090x mixer. The amp is a QSC Audio RMX2450 driving two Peavey SP 5xt speakers. All run through (except computer) a Furman PL-8 power conditioner.

Now the problem is that when I turn up the volume and a song plays a loud high seemingly of any kind I get a loud "chirp" or "squawk" like sound that really hurts to hear and I would imagine does damage to the system. I can't seem to figure out what is causing this. I have tried disconnecting the computer and using an mp3 player as a source and it still occurs. Audio sounds fine at lower volumes, only happens when I push for big sound (all within/under range of any clipping) and sound is not distorted. Any ideas what is wrong?

LordNor 15th May 2012 07:50 PM

I should also add that when I am pushing for loud volume the LCD monitor screen on the computer starts to show lines accross the screen as interference.

This system used to perform fine without any of these problems.

firechief 15th May 2012 08:17 PM

That busness about the screen going wacky is a real clue. I would suggest that the power amp is oscillating. How long are your interconnect cables? have you moved anything around about the time this started happening?. Check the cables for fraying or loose connections. Try different interconnect cables.

LordNor 15th May 2012 08:36 PM

Which cables? The ones connecting the computer to the mixer, the mixer to the amp, or power supply?

Enzo 15th May 2012 11:34 PM

Or possibly the amplifier system is over-taxing the mains circuit it is all plugged into.

imix500 16th May 2012 12:15 AM

I would also do a quick check and make sure nothing is routed back to itself or in a way to create an endless loop i.e.- oscillation.

firechief 16th May 2012 12:18 AM

Well for sure the cables between the mixer and the amp. Do you come off the sound card to the mixer. That would be my second choice.

LordNor 16th May 2012 03:03 PM

I am using a 1/8th inch stereo plug to RCA (composite) from the computers on-board sound card to the mixer. I have tried switching this cable and tried a different audio source with a different cable on a separate channel on the mixer. I dont see any cables in a loop, I have gone through and unplugged anything non-essential. I will try putting the amp on its own power circuit and see if that helps and report back. Please keep the ideas coming, and THANK YOU for all the help thus far.

Tajzmaj 16th May 2012 10:45 PM

Try to connect amplifier without Furman. It is possible that conditioner is overloaded.

Mike Caldwell 22nd May 2012 06:43 AM

Could be some old fashioned speaker bottoming out sound / voice coil hitting the back plate. Do you have a lot of low end boosted on the mixer and or in the computer.

Mike C.

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