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QSC processors acting weird while programming


Joseph Macry:
Has anyone had QSC DSP-4 processors freak out while programming?

I recently commissioned identical systems for two high school music rooms: portable rack with inputs, mixer, DSP and amp, that plugs into wall plate connected to speakers. Everything in stereo.

The DSP is QSC's DSP-4, mounted aback a CX-702 amp.

Short version: Hitting 'BYPASS' on a limiter module caused each channel to go into uncontrolled HF oscillation.  Also: DSP swapped channels in the middle of programming; happened on two separate units.

Details:  DSP was set up in stereo (dual mono). Each channel had: input, mutable noise generator, HPF, 30 band EQ, Limiter, gain stage, RMS meter and output.

I did the initial programming; a principal of sound consultant firm was there to inspect and fine tune. The Consultant was the one actually operating the software when this happened.

With the limiter block open, he hit BYPASS, and the channel went into high freq oscillation. The RMS meter showed peaked and clipping. I turned down the amp to prevent damage to the speaker.  Tried BYPASS limiter on the other channel, same thing happened.  This would not go away, even after cycling power and software. We could only kill the sound by removing the limiter blocks from the program.

The consultant took pink noise readings of the left speaker, and began setting filters. I pointed out he was working on channel 2, he should be on 1. No, he said, made an EQ change on 2 and we heard it in speaker 1.  Mixer showed signal on left, amp showed same, double checked wiring... DSP definitely had the channels backwards, modifying DSP channel 2 affected amp channel 1 and vice versa.  
The DSP went silent for half a second, then came back up with the channels correct!
We moved on to the other room. Noticed right off that DSP had the channels backwards, just like the first.  After about 5 minutes of programming, it flipped channels back!

We both stared in amazement.  We both wonder what these units are gonna do in operation.
We did an identical system last spring, and had no problem with that DSP.

Fred Thomke:
Hello Joseph,

PLEASE call or email me at QSC Audio.  This is NOT normal, and something definitely is wrong with this unit.  Let me know the serial number of the DSP-4 in question.  I will arrange to get you a replacement unit, overnight if necessary.

Did this unit EVER work correctly, or was it flaky right from the start?  How many modules -- just the one unit?

We will take care of this right away!


Joseph Macry:
Thanks Fred, I will send more info offline.

These problems happened on 2nd time powered up. (I did prelim setup last week, Consultant did final tuning this week.)
Channel swapping was on two separate units.


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