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PRX535 volume pumping and loss of low end.


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It's been a while since I've been on HC, hopefully this forum is as great as I remember.

 

I just got a pair of used PRX535s (older boxes as they have the 2408H compression driver which the schematic says hasn't been used in this box since 2008) and one of them was giving me some static on my first gig with them at a film screening, so I figured it was a loose connection or something simple. Upon further testing at home I was hearing the volume pump when playing back music, then all of a sudden the bottom dropped out. I opened up the box and the amp module has that electrical ozone burning smell. I don't see any busted caps or melted wires. I reconnected everything and the low end was back, but after a few min dropped out, and the volume is still pumping.

 

Any ideas of the cause or how to fix? Anyone else heard of this?

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I suspect that "volume pumping" will naturally occur if you drive the speakers too hard. You are likely hitting the compressors/protection system. You should likely be able to see a compression/limiting LED come on when this happens. Have you seen it?

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  • 2 weeks later...
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Sorry I didn't write sooner, I never got an email notification that there were replies.

 

I'm not hitting them hard at all. Playback of canned music from an iphone through a 1/8" to dual RCA Y-cable with RCA to 1/4" adapters into the 1/4" combo input on the PRX535s. dB meter reading 84dB c-weighted at 3' in front of the grill. One speaker is pumping, the other isn't. Switched channels from the iphone and the problem stays with the speaker, so it's not the source, or the cable. Only seems to be effecting the LF driver. Also get intermittent crackling from LF driver.

 

I was thinking maybe the power section to the LF driver after the crossover? Or something wrong with the crossover itself?

 

PRX535 has an overload and a signal LED, The Signal LED lights up, never hit overload. These were bought used and I'm sure they were hit hard. They were run with a DRPA for processing. I'm having this issue with no processing between the source and the speaker input.

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