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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Lounge FUD Forum Archive => Topic started by: Donnie Evans on June 15, 2009, 04:08:03 PM

Title: One amp channel has "cracking" sound....
Post by: Donnie Evans on June 15, 2009, 04:08:03 PM
Hey guys, hooked up our larger rig this weekend for the first time in a couple months... 2 yorkville ex1000 over sw900's.  The tops are the older version of the E215.  Powering everything off a carvin (meh..) DCM4000.  This is how we normally set up:

CH1- Main L
CH2- Main R
(really running in mono, so ch 1&2 have parallelled inputs)

CH3- Sub L
CH4- Sub R
(again, mono so inputs are parallelled)

So we get everything hooked up and I turn on the ipod and notice the horn in the left main has a slight cracking sound.  Not so much noticeable when music is coming through, but when it would get quiet, very noticeable.  I thought I had a horn going bad, or a bad connection in the cab, but to cover all the bases, I got a new cord... problem still there.  Almost didnt, but went ahead and swapped cords at the amp end to rule the amp out and the problem shifted to the right main.. so now I know it IS the amp it's narrowed down to channel 1.  We made it through the night with no problem using ch 3 and 4 for mains, and channel 2 for subs (just daisy chained subs).  

So the question is, what could cause this in the amp?  Loose input/output connections?  It did it using both NL4 and binding post output connections.  I've sent this monster back to Carvin for service before and its expensive to ship.  Plus we're out of the warranty now so we'd also have to pay for repair.  Is there anything I can pop the cover off and check for?

Thanks in advance.

Title: Re: One amp channel has "cracking" sound....
Post by: TJ (Tom) Cornish on June 15, 2009, 04:14:03 PM
With power removed, pop the cover and reseat all connectors inside the amp.  If that doesn't fix it then you may want to try this:

Do this at your own risk as you could potentially hurt yourself or damage the amp further, but if it's a last ditch before the dumpster effort and you're careful this can help identify loose or broken solder joints:

Get a wooden dowel to use as a non-conductive poking stick.  Take the cover off the amp, wire the system up with low gain and turn the power on.  Carefully press the dowel on different areas of the circuit board and see if you can make the crackling worse.  If you can, you may have localized the problem.  Visually inspect the area for broken leads on components or poor solder connections.

I fixed my MixWizard this way a few years back.  It had a cold solder joint from the factory that was driving me nuts.  I resoldered that joint and it's been 100% since.
Title: Re: One amp channel has "cracking" sound....
Post by: Donnie Evans on June 15, 2009, 04:17:49 PM
Thanks for the quick reply.  I'll try re-seating all the connections first.  Don't know if I'm up for prodding and poking around inside a live amp.  I'm not too shabby with the soldering iron though if I need to fix a spot.  I have a mix-wiz also and had a couple solder joints fail on the faders and found that it was a common occurrance so I re-soldered all the fader wires in it.  
Title: Re: One amp channel has "cracking" sound....
Post by: Tom Williams on June 17, 2009, 01:02:02 AM
If you do have a poke around pay special attention to any electrolytic capacitors. Did the problem get worse when the amp heated up? Make sure all o/p transistors are secure against the heat sink.
Title: Re: One amp channel has "cracking" sound....
Post by: Donnie Evans on June 17, 2009, 11:02:53 AM
It didn't start as soon as we switched the amp on, but after playing a couple songs on the ipod is when we noticed it and shortly after that we fixed it... so your question as to did it get worse when the amp heated up.. the answer is "I guess."   Confused

Title: Re: One amp channel has "cracking" sound....
Post by: Gus Housen on June 17, 2009, 03:24:29 PM
It could even be a dirty pot, I had a old CS-800 that did something similar.