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Old 20th October 2013
Here for the gear

Diagnosing a speaker versus amp problem

Hi all,

I've just assembled a simple system I'm pretty pleased with, but am encountering an issue with one channel in my highs not working properly. It seems that sound coming from my QSC GX7 amp is excellent in one channel, but spotty in the other. When I turn up the volume, it will increase momentarily and back off. It also doesn't sound clear, rather it sounds like there is some distortion. Did I possibly get a dud amp, or am I the dud here?

Here's the list of connections in my setup:
Macbook -> Peavey USB-P (Peavey :: USB-P USB Playback) - I added this per suggestions in this thread -> JBL JRX225 + Pyle Pro Pexa 3000 - OK or disaster?
Peavey USB-P -> 2 x JBL PRX718XLF subs via XLR cables.
JBL subs -> QSC GX7 amp (no filter or crossover, just the THRU signal (+4dBu) from the subs going into the amp)
QSC amp -> 2 x JBL JRX225 full range speakers

Does this configuration sound reasonable? (I really hope there isn't any damage potentially done with this configuration)

Here is some debugging I've done:
- run the subs alone, checking volume levels using balance and volume adjustments - the subs seem fine.
- full setup, but switched the outputs to the JRX 225 speakers. When I switch the output, the problem is not speaker-specific, it stays with output channel 2 of the amp.
- ran my cell phone (on low volume) via 1/8" to XLR adapter to the amp inputs to run just the amp and JRX225 speakers. The problem persists with channel 2 being problematic.
- also made sure the amp is in full range mode

Am I missing something here, or does it seem to be a defective amp?